The second
condition that must be met for the magnetic compass to be activated is that
what we’ll call the “compass on/off toggle” must be set to the “on”
position. The position of this
“toggle”, which can be either “on” or “off”, is not displayed in any of the Vista H's menus. The user can flip this toggle on and off at will by holding down the upper right button for several seconds. This will cause a message to appear on the screen saying "compass turned off" or "compass turned on". Regardless of the message, the compass will not really be on unless the time-speed parameters are also met. It is easy to accidentally flip this toggle while using the various buttons of the GPS. If this happens, the user can ignore this message if he or she is sure that the time-speed parameters do not actually allow the compass to stay on, or the user can simply press the upper right button again to be sure that the compass is turned off. By using this button, the user can make sure the compass is only on when actually needed, saving batteries, regardless of the setting of the time-speed interlock. Again, the magnetic compass will only stay on when the time-speed interlock is satisfied AND the on/off toggle controlled by the upper right button is set to "on". By setting the time-speed interlock to the maximum values noted above and leaving toggle in the "off" position, the user can make sure the magnetic compass will never accidentally get turned on.
15) “Heading”, “bearing”, and “course”
GPS users should
understand that in the absence of a magnetic compass function, a GPS unit
cannot really measure “heading”, only direction of travel over the ground.
With the Etrex
Vista (and Vista H and HCx), when the magnetic compass sensor is on, Garmin uses the word “heading”
to mean the direction that the nose of the aircraft (or more precisely, the
“nose” of the GPS) is pointing. When
the magnetic compass sensor is on, the Etrex Vista cannot display the current
direction of travel over the ground, except in the form of the “breadcrumb
trail” that is laid down on the map screen.
When the magnetic compass is switched off—which it always should be
during flight—then the word “heading” refers to the current direction of travel
over the ground, as derived from the GPS satellites.
The heading
indicator display—i.e. the display that looks like a compass—displays
“heading”, as defined above. When the
magnetic compass is switched off, this will reflect the direction of travel
over the ground.
The “bearing” is
the direction to the target waypoint at any given moment.
Now we’ll take a
moment to define the concept of a “course” line, as used by Garmin in the
context of the GPSmap series and other similar handheld GPS units: at the moment that a “goto” function is
activated, a fixed “course” line is created, which is the line extending from
the aircraft’s location at moment that the “goto” function was started, to the
target waypoint. Once a “goto” function
has been activated, as the aircraft continues to fly, the “bearing” to the
target waypoint may change, but the “course” line remains completely fixed in
space, until the navigation to the waypoint is discontinued or re-started with
the same waypoint or with a different waypoint. Even if the aircraft strays “off course” by many miles, the
numerical reading in the “course” data field (if present) will remain fixed
until the navigation to the waypoint is discontinued or re-started with the
same waypoint or with a different waypoint.
With Etrex Vista (and Vista H and HCx),
the user can configure the GPS so that either a “course line” or a “bearing
line” appears on the map screen when the GPS is navigating toward a
waypoint. As noted above, the “course
line” remains fixed in place on the map, while the “bearing line” moves so that
one end is always attached to the aircraft icon, while the other end remains
fixed at the destination waypoint.
The user can also
configure the GPS so the either a “course pointer” or a “bearing pointer”
appears on the heading indicator display.
The “course pointer” is an HSI-style display: the orientation of the
course line pointer remains fixed with relation to the azimuth dial, but the
course line pointer slides sideways to show that the aircraft is “off
course”.
For soaring
flight, I always choose the “bearing” option for both the map screen and the
heading display screen. In fact, for
soaring flight, I almost never allow my GPS to display any information relating
to “course”; I’m generally much more interested in the “bearing” from my
current position to the destination waypoint.
16) “Current glide ratio” and “glide ratio to destination” displays
Garmin handheld
GPS's with barometric pressure sensors, including the Garmin GPSmap 76S,
GPSmap76C/Cx/CS/CSx, GPSmap60/60C/Cx/CS/CSx, and Etrex Vista/ Vista H/ Vista HCX,
include "current glide ratio" and "glide ratio to
destination" displays. These
functions are quite useful. By
comparing the two numbers, one can get a sense of whether the glider will reach
the target with altitude to spare, or will not have enough altitude to reach
the target.
The “current
glide ratio” display on these GPS’s is extremely responsive. This is a mixed blessing. In very smooth air, the effects of a change
in airspeed can be seen almost instantly, after waiting just a few seconds for
the aircraft's sink rate to stabilize.
In turbulent air the display is so “twitchy” that it is not really very
useful for fine-tuning the pilot’s choice of speed-to-fly. It would be nice if the user could select
for the “current glide ratio display” to be averaged over a slightly longer
time interval on these GPS’s, so that it would function more like the digital
“current glide ratio” display on some GPS-compatible variometers like the
Brauniger IQ Comp GPS. This would make
the “current glide ratio” display slightly more useable for fine-tuning the
pilot’s choice of speed-to-fly.
However, even in turbulent air, and even given the “twitchiness” in the
“current glide ratio” display, a rough comparison of the “current glide ratio”
with the “glide ratio to destination” will give a good idea of whether or not
the glider is currently on a glide path that will reach the target destination
with altitude to spare or fall short of the target destination, assuming that
the current atmospheric conditions will continue all the way to the
target.
A "glide ratio to destination” display is always
intrinsically much more stable than a "current glide ratio" display,
because the "glide ratio to destination " function depends only on
the glider's position in space relative to the target, not on the glider's
horizontal and vertical velocities. The
“glide ratio to destination” display is not dependent upon an accurate
measurement of the glider’s vertical speed at any given moment. An updraft or downdraft can produce a very
large, immediate change in the “current glide ratio”, but will only produce a
gradual change in the “glide ratio to destination.”
A long-term trend in the “glide ratio to destination” function
gives a pilot some useful information.
For example, in a sailplane, if a pilot sees the “glide ratio to target”
slowly scroll from “30” down to “25” over the course of several minutes, this
indicates that the glider will overfly the target with altitude to spare,
assuming that the current atmospheric conditions continue all the way to the
target. Conversely, if the pilot sees
the “glide ratio to destination” slowly scroll from “30” up to “35” over the
course of several minutes, this indicates that the glider will run out of
altitude before reaching the target, assuming that the current atmospheric
conditions continue all the way to the target.
For hang gliding and paragliding applications where glide ratios are
often below 10:1 and can even drop to 5:1 or less when a strong headwind is
present, a “tenths” digit in the “glide ratio to destination t” display is very
useful for helping a pilot to detect slow trends in the “glide ratio to
destination” display. For example, if
over a period of several minutes, the “glide ratio to destination” figure
slowly scrolls from "4.8" to "4.7" to "4.6", this
lets the pilot know that he will overfly the target with altitude to spare,
assuming that the current atmospheric conditions continue all the way to the
target. On the other hand, if over a
period of several minutes, the “glide ratio to destination” figure slowly
scrolls from "4.7" to "4.8" to "4.9", this lets
the pilot know that he will not be able to reach the target, if the current
atmospheric conditions continue all the way to the target. For hang gliding and paragliding
applications, a “glide ratio to destination” display is significantly more
useful if it has a “tenths” digit, than if it does not.
The “glide ratio
to destination” display on handheld Garmin GPS’s with pressure sensors does not
include a “tenths” digit. Perhaps in a
future software update for these GPS units, Garmin will create a “tenths” digit
for the “glide ratio to destination” function, at least in cases where the
glide ratio to target has dropped below 10:1.
In fact this would be my number one suggestion to Garmin for improving
the functionality of their GPS’s for hang gliding and paragliding applications.
Pilots may
occasionally encounter a rather peculiar problem with the “current glide ratio”
function on handheld Garmin GPS’s with barometric pressure sensors-- if the
satellite reception is poor, the “vertical speed” display will scroll to zero and
the “current glide ratio” display will scroll to infinity. For more, see the related article on this
website entitled “Notes on the glide ratio functions of some Garmin GPS receivers
with pressure sensors”.
For most soaring applications, the satellite reception is good enough
that this problem is rarely encountered.
However, I’ve occasionally encountered this problem when flying with my
older Etrex Vista attached to the down tube of my hang glider. I’ve always been able to cure this by
changing the angle of the mount so that the face of the Vista pointed more
upwards and less sideways.
Since this problem is related to the quality of the reception of the GPS signal, it will probably be very uncommon in GPS units with high-sensitivity receivers, such as the Vista H, Vista HCx, and GPSmap76CSx.
17) “Estimated time of arrival” computer
The “estimated
time of arrival” computer isn’t useful for soaring flight, but it is useful
during cross-country flight in an airplane, where it seems to be quite
accurate. The “estimated time of
arrival” computer even seems quite accurate during most driving situations,
even when it is not possible to travel directly toward the destination (e.g.
the roads run north-south and east-west and the destination lies to the
northwest.) The computer doesn’t seem
to rely too heavily on the velocity made good toward the destination at any
given moment. The behavior of the
“estimated time of arrival” computer seems roughly consistent with the
following model: an eta computer could be programmed to assume that the vehicle
will continue travelling at its current speed and direction until the target
destination lies abeam the current direction of travel, and then will turn 90
degrees and travel directly toward the target destination, keeping the same
forward speed.
18) “Battery save” mode
The Etrex Vista H doesn't have a user-selectable "battery save" mode. Garmin appears to have done a good job of engineering the GPS for good responsiveness combined with long battery life.
19) Notes on
track logs: “active logs” and “saved tracks”
We’ll now turn
our attention to the track logs generated by the Garmin Etrex Vista H. The Vista generates two different kinds of
track logs, both of which can be accessed by downloading the GPS data to the
“MapSource” program. We’ll call these
two different types of track logs the “active logs” and the “saved tracks”.
The phrase
“active log” never appears on anywhere on the screen of the Etrex Vista H, but
will be familiar to anyone who has downloaded data from the Vista to MapSource,
as we’ll see shortly. If the unit is
being used in the “track off” mode, then no “active log” is being
generated. Otherwise, a new “active
log” begins every time the GPS unit acquires a satellite lock, or loses the
satellite lock, or is put into “GPS off” mode.
(After the unit loses the satellite lock or is put into “GPS off” mode,
the location is assumed to be fixed at the last known position, but new
altitude data continues to be recorded.)
Each “active log” is comprised of many individual “track points”. For each “active log” track point, the GPS
records time and date as well as location.
When an “active log” is viewed with the “MapSource” computer program,
each “active log” track point is displayed along with the date, clock time (in
hours, minutes, and seconds), altitude, leg length (i.e. distance to the next
track point), leg time, leg speed, leg course (which in this context means the
direction of travel to the next track point), and position (latitude and
longitude).
The “active logs”
are not listed on the GPS’s “tracks” menu.
However the “active logs” are used to draw the “breadcrumb trail” on the
map screen of the GPS: the “breadcrumb trail” represents all the active logs
that are currently stored in the GPS, and shows everywhere that the GPS has
been since the track log was last cleared (or at least back to the oldest
“active log” track point that has not yet been overwritten by newer track
points.) The “active logs” are also
used to draw the altitude-versus-time plot or altitude-versus-distance plot on
the “altitude” screen of the GPS.
Again, these plots show the entire history since the last time that the
track log was cleared, back to the oldest “active log” track point that remains
in the “active log” memory.
When GPS data is
downloaded to MapSource, the “active logs” appear on MapSource’s “tracks” page,
and have names like “ACTIVE LOG”, “ACTIVE LOG 001”, “ACTIVE LOG 002”, etc. In MapSource, the user can re-name the
active logs if he wishes. In MapSource,
the user can also select a specific active log to display as a track on the map
or as an altitude-versus-distance plot.
MapSource cannot display an altitude-versus-time plot. With MapSource, several different “active
logs” can be joined together into one.
Active logs can be uploaded from MapSource to the GPS, as we’ll see in a later section of this article.
The Etrex Vista H
can store up to 10,000 “active log” track points in all. The fraction of the “active log” memory that
has been used up is displayed near the top of the “tracks” menu screen near the
words “track log”. When there is no
more room to record fresh “active logs” without overwriting older “active
logs”, the “track log” memory indicator will read 100%. Deleting some of the “saved tracks” that
appear on the “tracks” menu screen has no influence on the amount of memory
that is available for recording new “active logs”—the “saved tracks” and the
“active logs” are stored in different memory areas, and the memory indicator
near the top of the “tracks” menu screen refers only to the memory used by the
“active logs”, not to the memory used by the “saved tracks.” If the user has selected the “wrap when
full” option on the “set up track log” menu, then once the “active log” memory
space is full, the oldest “active log” will began to be over-written in a point-by-point
fashion (i.e. the entire oldest “active log” will not disappear in one
instant). Pushing the “clear” button on
the “tracks” menu screen will erase all the active logs and reset the “track
log” memory indicator to zero. Pushing
the “clear” button on the “tracks” menu screen will not erase any of the “saved
tracks” that are listed on the “tracks” menu screen. We’ll discuss the “saved tracks” in more detail shortly. After downloading the track log to a computer,
it’s a good idea to push the “clear” button on the “tracks” menu screen to
erase all the active logs, so that the “track log” memory indicator will be
reset to zero.
In the “track log
setup” menu, the user can control how often a new track point is added to the
current “active log”. The user can
specify a time interval or a distance interval for adding new points to the
“active log”. However, I prefer to use
a third option called “auto”.
One of the chief
advantages of the “auto” mode is that new active log points are added very
infrequently (often only 2 per minute) when the GPS is not moving, so the user
can switch the GPS on well before starting a flight and not worry that the
active log memory is being needlessly consumed. The only time this is not true is when the wind is gusty. The barometric pressure sensor is affected
by wind gusts, which create apparent changes in altitude, and trigger the
recording of more track points.
In the “auto”
mode, the GPS creates new “active log” track points at whatever rate is needed
to create a high-resolution trace of the flight path. New “active log” track points are added much more frequently when
the direction of travel is rapidly changing (e.g. when a glider is thermalling)
than when the direction of travel is nearly constant. New “active log” track points are also added much more frequently
when the speed of travel is rapidly changing (e.g. when an aircraft is flying
in circles at a constant bank angle and airspeed, in a strong wind) than when
the speed of travel is nearly constant.
Even if the vertical speed is roughly constant, new “active log” track
points are added much more frequently when the altitude is changing than when
the altitude is nearly constant. If the
vertical speed is changing rapidly rather than constant, new “active log” track
points appear to be recorded more frequently than when the vertical speed is
constant.
In the “auto”
mode, the user can also select whether the “active log” track points are added
“most often”, “more often”, “normal”, “less often”, or “least often”. In some Garmin GPS units such as the Etrex
Legend, I’ve found a marked difference (e.g. a factor of 2.4 or more) in the
recording frequency between the “auto, most often” mode and the “auto, least
often” mode. Oddly enough, in the case
of the Etrex Vista and the GPSmap 76S, the recording interval in the “auto,
least often” mode seems to often be only about 1.4 times as long as the
recording interval in the “auto, most often” mode, and often—especially during
thermal flights with a great deal of circling-- the difference in the length of
the recording interval between these two modes sometimes becomes almost
negligible (e.g. a factor of 1.2). Also, with these 2 GPS units, there seems to
be very little difference in the length of the recording interval between the
“auto, normal” mode and the “auto, least often” mode. With these 2 GPS units, when the “active log” track memory is
starting to fill up, switching from “auto, most often” to “auto, normal” or
“auto, least often” will not necessarily produce a dramatic increase in the
amount of flight time that will fit into the remaining portion of the “active
log” track memory.
Here are some
examples of typical “active log” recording intervals for the Etrex Vista or
GPSmap 76S in the “auto, most often” mode:
Example 1:
shortest recording interval seen during a typical thermalling flight in a hang
glider: one “active log” track point every second, which if sustained
indefinitely, would yield only 2.8 hours of recording time. I’ve only seen this high recording rate
sustained for a minute or two at a time, typically during strong thermal climbs
in strong wind.
Example 2:
average recording interval over the entire length of a typical thermalling
flight in a hang glider: one “active log” track point every 2 to 3 seconds,
yielding 5.6 to 8.3 hours of recording time.
I’ve never seen the recording interval averaged over an entire flight in
a hang glider drop below one “active log” track point every 2 seconds, so I
suspect that a pilot can always count on at least 5.6 hours of recording time
for a hang gliding flight.
Example 3:
average recording interval during a ridge-soaring flight in a hang glider: one
“active log” track point every 3.5 seconds or longer, yielding 9.7 or more
hours of recording time.
Example 4:
average recording interval over the entire length of a typical local
thermalling flight in a low-performance sailplane: one “active log” track point
every 2 to 3 seconds, yielding 5.6 to 8.3 hours of recording time.
Example 5:
average recording interval during a flight segment in a light plane where the
heading was roughly constant and the vertical speed changed frequently: one
“active log” track point every second, yielding 2.8 hours of recording time.
Example 6:
average recording interval during a prolonged full-power climb in a light
plane, with a roughly constant airspeed and heading and vertical speed: one
“active log” track point every 1.5 seconds, yielding 4.2 hours of recording
time
Example 7:
average recording interval during a high-speed flight segment in a light plane,
where the speed, heading, and altitude were roughly constant: one “active log”
track point every 5 seconds, yielding over 13 hours of recording time.
Example 8:
average recording interval while driving a car at highway speeds over a road
with many long, straight, flat sections: one “active log” track point every 4
seconds, yielding over 11 hours of recording time
It’s interesting
to speculate whether a paraglider, hang glider, or sailplane would tend to
experience the shortest “active log” recording interval during thermalling
flight. I suspect that a lower-speed
aircraft would generally experience a shorter “active log” recording interval
than a higher-speed aircraft, because the lower-speed aircraft experiences a
higher turn rate for a given bank angle than a higher-speed aircraft does. However, a given angular change in heading
creates a greater change in predicted position when the speed of travel is high
than when the speed of travel is low, so perhaps the “active log” recording
interval during circling flight ends up being relatively independent of
airspeed. I’ve collected less data for
sailplanes than for hang gliders, but as far as I’ve been able to tell, the
average “active log” recording interval for both of these aircraft types has
been roughly similar during thermalling flight.
In summary, when
using the “auto, most often” mode a pilot can generally expect to get at least
5.5 hours of “active log” recording time for most flights in light airplanes,
sailplanes, hang gliders, and paragliders, and can generally expect over 9
hours of “active log” recording time while ridge-soaring. However in certain situations the “active
log” track recording interval can fall to one point every second, which only
yields 2.8 hours of recording time. It
would be very unusual for the GPS to use this high recording rate over the
length of an entire flight, but this might be possible if the flight followed a
very unusual profile such as series of extremely rapid climbs and descents,
e.g. during aerobatics. Switching to
the “auto, least often” recording mode will produce some increase in the amount
of available recording time, but the increase will not necessarily be very
large. If a pilot wants to be sure that
the GPS will retain a set of “active logs” that span the entire length of a
flight, he should set the GPS to the “time” mode rather than the “auto” mode if
the flight will likely be longer than 5.5 hours, or in the case of a ridge
soaring flight in a hang glider, longer than 9 hours, or in the case of a
flight involving an unusual number of very rapid climbs and descents (e.g.
during aerobatics), longer than 2.8 hours.
During the course
of a long flight, if a pilot is concerned about over-writing the start of the
first “active log”, he can bring up the “tracks” menu to see what fraction of
the “active log” memory remains, and he can then change the “active log” track
recording interval if necessary. Of
course, this strategy only works if the pilot has selected the “clear track log”
option before flight, or after the last time he downloaded the GPS data to a
computer, so that there are no old unwanted “active logs” sitting in the
“active log” memory area.
I normally set my
GPS to record in the “auto, most often” mode.
If my actual time in flight exceeds 5 hours (or 9 hours during a
ridge-soaring flight in a hang glider),
I make a point of checking the amount of space remaining in the “active
log” memory every half hour or so. If I
see that the “active log” memory is approaching 90% full, I change the “active
log” recording interval to the “time, 20 seconds” mode. With 1000 “active log” track points
remaining, this yields 20,000 seconds or 5.6 hours of additional recording
time.
When the “active
log” memory is running low, another alternative is to simply use the “save
track” option in flight. As we’ll see
in a moment, the “saved tracks” created by this method are separate from the
“active logs” that we’ve been discussing, and contain less detail than the
“active logs”, but at least some record of the start of the flight will be
preserved even if the corresponding “active log” track points are overwritten.
Of course,
another strategy is simply to use the “time” recording mode rather than the
“auto” recording mode. For example, a
recording interval of 3, 4, or 5 seconds will allow the GPS to retain “active
logs” spanning 8.3 hours, 11.1 hours, or over 12 hours respectively, and a
recording interval of 10 seconds will allow the GPS to retain “active logs”
spanning more than 24 hours. One of
these might be a good setting for a second, “backup” GPS. For a multi-day flying trip where the user
has no access to a computer for downloading GPS data, an even longer recording
interval might be appropriate.
None of these
adjustments to the rate at which new track points are added to the “active log”
has any effect on the rate at which the map display screen is updated, or on
the rate at which the numerical data display fields are updated, or on the rate
at which new data is sent out through the data port to an attached variometer,
barograph, etc. The numerical data
fields, moving map screen, and compass-like display screen all appear to be
updated about once per second, regardless of the rate at which new track points
are added to the “active log”.
The very latest
leg of the “breadcrumb trail” on the GPS’s map screen is anchored at one end to
the last “active log” track point, and is attached the other end to the moving
triangular icon representing the current position of the GPS. This means that if the GPS is set to record new
“active log” track points at a very low rate, the latest leg of the “breadcrumb
trail” on the GPS’s map screen will not always offer an accurate depiction of
the current direction of travel over the ground. In this case, the orientation of the triangular icon representing
the current position of the GPS will still continue to show the current
direction of travel over the ground.
As an aside, the
Etrex Vista’s pressure-versus-time plot, as opposed to the
elevation-versus-time plot or elevation-versus-distance plot, appears to be
based upon a separate log that is distinct from the “active logs” that we’ve
been discussing here. This separate log
is not cleared when the active log is cleared via the “clear” button on the
“tracks” menu. This separate log is not
downloaded to MapSource along with the other “active logs”.
The second type
of track log generated by the Etrex Vista contains less detail than the “active
logs” that we’ve been discussing up to this point. We’ll call these other track logs the “saved tracks”. “Saved tracks” have names like “20-JUN-06
02”, or whatever name the user substituted while saving the track. Like “active
logs”, “saved tracks” are comprised of many individual “track points”. For each “saved track” track point, the GPS
records only the position, not the date or time. When a “saved track” is viewed in “MapSource”, each “saved track”
track point is displayed along with the altitude, leg length (i.e. distance to
the next track point), leg course (which in this context means the direction of
travel to the next track point) and position (latitude and longitude). Since the “saved track” points contain no
time or date information the date, clock time, leg time, and leg speed cannot
be displayed.
A “saved track”
only samples a small portion (often 1/5 or less) of the track points that make
the corresponding “active logs”. A new
“saved track” begins every time the user presses the “save” button on the
“tracks” menu screen. One “saved track”
can cover many days and can sample points from many different “active
logs”. If the user selects the “save
all” motion, then the new “saved track” will encompass all the “active logs”,
i.e. the new “saved track” will encompass the entire length of the “breadcrumb
trail” that appears on the map screen of the GPS. The GPS will also suggest other shorter intervals such as “save
since noon”, etc. Pressing the “save”
button on the “tracks” menu screen to create a new “saved track” has no effect
on the amount of memory space left for recording “active logs”. Pushing the “clear” button on the “tracks”
menu screen will erase all the “active logs” and reset the “active log” track
log memory indicator to zero, but this will not erase any of the “saved
tracks”. Up to 10 “saved tracks” may be
stored in the memory of the Etrex Vista.
The “saved tracks” currently stored in memory are listed on the “tracks”
menu page.
When the GPS is
saving a “saved track”, the more track points in the corresponding “active
logs”, the smaller the fraction of these points that will be incorporated into
the “saved track”. The maximum number
of points that can ever be incorporated into a “saved track” is 750. In
practical terms, this means that a saving a fresh “saved track” after each
flight will capture much more resolution in the “saved track” than will waiting
until the “active log” track memory is nearly full after several days of flying
and then saving the entire “active log” as a single “saved track”. Since the active logs can span up to 10,000
track points, and a “saved track” can only include up to 750 track points, the
latter course of action would mean that the resulting “saved track” would only
capture about 7% of the track points in the corresponding set of “active logs”.
When a pilot
presses the “save” button on the “tracks” menu screen, creating a “saved
track”, and then selects the “show on map” option so that that “saved track”
remains visible on the map screen of the GPS, he may notice that there are
really two different track lines that lay on top of each other. One of these lines is the “breadcrumb trail”
or “active log”. This line is usually
quite smooth even during tight circling maneuvers. The other of these lines is the “saved track”, which contains
many fewer track points and therefore may be much more “jagged” in appearance
than the “active log”, especially during circling maneuvers. On the Etrex Vista, both the “active logs”
and the “saved tracks” are depicted by similar heavy solid lines; the only
visible difference between the two is that during circles or curves, the
“active log” is smoother and the “saved tracks” are more “jagged”. As the pilot continues to use the GPS,
eventually that portion of the “breadcrumb trail” or “active log” will be
overwritten (assuming that the user has selected the “wrap when full” option)
and only the coarser “saved track” will remain.
Any given “saved
track” will only be visible on the map screen of the Etrex Vista if the “Show
on Map” option has been checked on the detailed menu for that track, which can
be accessed from the “tracks” menu page.
This box is checked by default when “saved tracks” are downloaded from
“MapSource” to the GPS, but not when a new “saved track” is created by using
the “save” button on the “tracks” menu screen.
Likewise, when GPS data is downloaded to MapSource, a careful
examination of the MapSource map screen will reveal that there are often two
track lines overlain on top of each other.
Again, the smoother line is the “active log”, and the coarser line is
the “saved track”. (If the user has
pressed the “save” button on the “tracks” menu several times, there may be
several different “saved tracks” that sample all sample a given “active log”,
in which case there will be several different track lines all overlain on top
of each other.) Of course, if the
“active log” track memory became full and began to overwrite itself before the
GPS data was downloaded to MapSource, then the “active log” for a particular
segment of a “saved track” may be absent.
Similarly, if the user has not exercised the “save track” option before
downloading the data to MapSource or before a given portion of the “active log”
track memory was overwritten, then there may be no “saved track” encompassing a
particular “active log”.
Since the “active
logs” contain more detail than the “saved tracks”, the only real reasons to use
the “save” button on the tracks menu screen to create a “saved track” are to
capture some of the corresponding the “active log” points before they are
over-written, or to create a single record that encompasses an entire flight
(which may include many different “active logs” if the satellite lock was lost
and re-acquired several times), or to attach a name to a track for future
reference. However, in Map Source,
several “active logs” can be consolidated into a single record, and any
name the user desires can be attached to any “active log” or “saved
track”. Therefore if the user is in the
habit of downloading the GPS data to a computer at the end of each flight or at
the end of each flying day, and is able to capture all of the “active log”
track points before any are overwritten, there is no real need to use the
“save” button on the tracks menu screen.
On the other hand, if the user does not plan to download the GPS data to
a computer very often, or if the user simply doesn’t care to preserve the high
level of detail (i.e. the high resolution, and the time and date information)
that is characteristic of the “active logs”, then he’ll likely want to use the
“save tracks” feature at the end of each flight or at the end of each flying
day to capture a subsample of the “active log” track points in the form of a
“saved track” before that portion of the “active log” is overwritten. At this time, it’s often convenient to give
a descriptive name to the “saved track” that is being saved, so that when the
GPS data is downloaded to MapSource at some later time, it is immediately clear
what the various “saved tracks” represent.
(Bear in mind that the individual track log points for the “saved tracks”
contain no time or date information.)
As we’ve already noted, saving a fresh “saved track” at the end of each
flight will sample a higher fraction of the “active log” track points than will
waiting to save a “saved track” when the “active log” memory is nearly full
after several days of flying.
Conversely, since the GPS can only hold 10 “saved tracks”, if the goal
is to extend the GPS’s memory as far as possible without regard to the level of
detail that is captured, the user should set the track log to record very
infrequently, and then should wait until the “active log” track memory is
nearly full to use the “save tracks” feature to capture a subsample of those
“active log” track points in the form of a single “saved track”. Then the user should clear the “active log”
track memory, erasing the “active logs” or “breadcrumb trail”, and repeat the
process when the “active log” track memory becomes full again. With this procedure, the GPS’s memory may be
stretched to encompass many days of flying.
However, the user should remember that each “saved track” contains no
information as to time or date, other than whatever information the user has
included in the title.
In actual
practice, I make a point of saving a new “saved track” after each flight. At the end of a day of flying, I download the
tracks to a computer, which also captures not only the “saved tracks”, but also
all the “active logs”, that are associated with that day of flying. Then I go through the downloaded “active
logs” and “saved tracks” in MapSource and delete any that are of no lasting
interest. Finally I select the “clear
track log” option on the “tracks” menu of the GPS, which deletes all the active
logs in the GPS’s memory. This isn’t
really necessary, because those active logs would eventually be overwritten
with new data, but it prevents me from downloading the same “active logs” to a
computer on some later date, which would use unnecessary memory space. Also, by not keeping old “active logs” in
the GPS’s memory, I ensure that should I find myself in the middle of a very
long flight, I can easily check to see if the “active log” points corresponding
to the beginning of that flight are in any danger of being over-written, and
taken action accordingly.
Unfortunately, on the Vista H, the user must use the select the starting and ending points used to create a "saved track". To me this is less convenient than the system used on the older Etrex's and the GPSMap76S, when the user was offered a choice of starting times for the saved track. As a result, I tend to ignore the "save track" feature completely and simply make sure I download my active log before it is overwritten.
When multiple
“saved tracks” are created on one day, the Etrex Vista will suggest names like
“20-JUN-06”, followed by “20-JUN-06 02”, followed by “20-JUN-06 03”, etc. We’ll call the suffix “02” or “03” in the
above example the “sequence number”. Saved tracks are always assigned the lowest “sequence number” that
is available, which means that under certain specific circumstances, the “saved
tracks” can end up not being numbered chronologically. For example if the user does 3 “save track”
operations, and then deletes the second “saved track”, and then does one more
“save track” operation, the 4th “saved track” will be assigned the now-vacant
sequence number of “02” rather than “04”, even though an earlier “saved track”
still holds the “03” sequence number.
20) Notes on waypoints
With the Etrex
Vista H, it is fairly easy to create a waypoint in mid-flight. Simply hold the joystick button down for 2
seconds, and then push the joystick down one more time. When creating a new waypoint, the user must
take care not to move the joystick to the side or several extra steps will be
needed. With each waypoint, the GPS
saves the position (latitude and longitude), altitude, and date and time of
creation. Unfortunately, at least 4 additional operations are needed to initiate a "goto" function toward the new waypoint! This is very cumbersome and a departure from the system used in the older Etrex's (Vista, etc) and the GPSMap76S.
Waypoints are not
automatically incorporated as track points in the “active log” or “saved
tracks”.
On the Etrex
Vista H, it is very easy to find the bearing and distance to a waypoint, even if
the GPS is not actively navigating toward that waypoint. Simply call up a list of nearest waypoints
(or an alphabetical list of waypoints), and use the joystick to move the cursor
over one of them to highlight it. The
GPS will give a continually-updated reading of the bearing and distance to that
waypoint. This could be extremely handy
for transmitting a location in an emergency, e.g. when a pilot has deployed his
reserve parachute.
21) List of
settings
Here is a list of
some of the settings I use for my Etrex Vista.
Bear in mind that selecting “500 miles” means that a feature will always
be shown and selecting “20 feet” means that a feature will almost never be
shown.
I use the 4
numerical data fields on the map screen and/or compass display screen to display "speed", "heading", “glide ratio”, and “glide
ratio to destination”, and I use the 2 numerical data fields on the
compass-like screen to display “speed” and “heading”. On the trip computer
screen I set the 9 numerical data fields to show “speed”, “heading”, “bearing”,
“final distance”, “glide ratio”, “glide ratio to destination”, “time of day”,
and other variables chosen from “sunrise”, “sunset”, "time of day", or "accuracy of GPS".
On the first tab
of the “set up map” menu: orientation
“north up”, auto zoom “off”, detail “most”.
On the second tab
of the “map setup” menu: saved tracks “500 mi.”, track log “500 mi.”, track points “100000”, goto line
“bearing”.
On the third tab
of the “map setup” menu: map points "auto", user waypoints “500
mi.”, street label "auto", land cover "auto".
On the sixth tab
of the “map setup” menu: marine colors "off" (except during prolonged flights over some features like state parks,
where the “water” display mode seems to give a better view.)
On the “setup
track log” submenu of the “tracks” menu: “wrap when full” box checked yes,
record method “auto”, interval “most often”.
On the “heading”
submenu of the “setup” menu: display “degrees”, north reference “true”, auto
compass switch 1) switch to compass heading when below “0 mph”, 2) use for more than “180
seconds”. These settings ensure that the magnetic compass will stay off.
(Alternate settings for hiking: switch to compass heading when below “10 mph”, 2) use compass heading when below 10mph for more than “5
seconds”.0 These settings allow the user to toggle the magnetic compass on and off at will, with the upper right button, while travelling on foot. The magnetic compass is convenient because it makes for a more stable display of "heading" while travelling at low speeds, so long as the GPS unit is held roughly level, but the magnetic compass also increases the drain on the batteries.
On the “system”
submenu of the “setup” menu: GPS “normal” or "battery saver", WAAS “enabled”, altimeter auto calibration
“off” (or occasionally “on” for operation in areas where I can’t set the
altimeter to match a known reference altitude; also set auto calibration "on" for all non-flying applications.)
On the “units”
submenu of the “setup” menu: position format “degrees, minutes, decimal
minutes”, map datum “WGS 84”
22) Additional
notes on track logs: uploading “active logs” and “saved tracks” from MapSource
6.9.1 to the Etrex Vista
As noted above,
when GPS data is downloaded to MapSource, the “active logs” as well as the
“saved tracks” appear on MapSource’s “tracks” page. The “active logs” have names like “ACTIVE LOG”, “ACTIVE LOG 001”,
“ACTIVE LOG 002”, etc. The “saved
tracks” have names like “20-JUN-06 02”, or whatever name the user substituted
while saving the track. In MapSource,
the user can re-name any “active log” or “saved track”. In MapSource, several different “active
logs” and/or “saved tracks” can be
joined together into one single “active log” or “saved track”.
In MapSource, the
user can also select a specific “active log” or “saved track” to display as a
track on the map or as an altitude-versus-distance plot. MapSource cannot display an
altitude-versus-time plot.
In MapSource,
parts of “active logs” (including the time and date information) can be spliced
into “saved tracks” (which lack time data), and vice versa. The actual position data for individual
track log points cannot be changed, but track points can be deleted. This will create a change in the leg length
and leg course values displayed for the preceding track point, as well as the
leg time and leg speed values (if present.).
Note that now the distinction between “active logs” and “saved tracks”
is starting to blur—once we start to manipulate tracks in MapSource, splicing
pieces of “saved tracks” into “active logs” or vice versa, we no longer can
categorize a track segment as a “saved track” or an “active log” depending on
whether time and date information is present or not.
In fact as far as
MapSource is concerned, there is no distinction at all between an “active log”
and a “saved track”. However, as data
is uploaded from MapSource to the Etrex Vista, the GPS will treat the data
differently depending upon whether it recognizes the segment as an “active log”
or as a “saved track”.
When data is
uploaded from MapSource to the Etrex Vista, any segment whose name begins with
the words “active log” (not case-sensitive) is treated as an “active log”, and
any segment whose name does not begin with the words “active log” is treated as
a “saved track”. This is true even if
the “active log” was originally a “saved track” whose name has been changed to
begin with the words “active log”, or vice versa. This is also true even if the “active log” has had bits of “saved
tracks” spliced into it, or vice versa.
So the ultimate definition of an “active log” is any track segment whose
name begins with the phrase “active log” (not case-sensitive), and the ultimate
definition of a “saved track” is any track segment whose name does not begin
with the phrase “active log”. To take a
rather complicated example, if the user goes into the “saved tracks” menu
screen of the Etrex Vista and changes the name of one of the “saved tracks” to
“ACTIVE LOG”, and then downloads that track segment to “MapSource”, then if
that segment is ever uploaded back to the Etrex Vista, the uploaded segment
will be treated as an “active log” rather than a “saved track”!
In addition to
the limit of 10,000 total “active log” track points that can be stored in the
memory of the Etrex Vista, there may be a limit to the total size of any one
“active log” that can be uploaded successfully from MapSource to the Etrex
Vista, but I’ve not encountered this limit in actual practice.
As an “active
log” is uploaded from MapSource, its name will not appear on the “saved tracks”
screen, but the “tracks log” memory indicator will show an increase in the
amount of memory that is currently in use, and the segment will appear on the
“plot versus distance” page of the elevation screen, and the segment will be
visible in the “breadcrumb trail” that represents the cumulative total of all
the “active logs” in memory. This is
all characteristic of the way that the Etrex Vista treats any “active
log”. The time-related and date-related
data normally present in an “active log” are preserved when the “active log” is
uploaded from MapSource to the Etrex Vista.
As an “active log” (e.g. “ACTIVE LOG 004” or “active log great flight
June 6”) is uploaded from MapSource to the GPS, its name will be automatically
modified to the standard “active log” format of the words “ACTIVE LOG” followed
by three numbers (e.g. perhaps becoming “ACTIVE LOG 041”), and these three
numbers will be consecutive to the numbers of all the other “active logs” currently
in memory. The “active logs” in memory
are normally numbered from oldest to newest (e.g. “ACTIVE LOG” followed by
“ACTIVE LOG 001” followed by “ACTIVE LOG 002”, where “ACTIVE LOG” is the oldest
and “ACTIVE LOG 002” is the newest), but when an older “active log” is uploaded
from MapSource to the Etrex Vista, it will receive a number consecutive to all
the other “active logs” in memory at that moment, even if it actually
represents a much older track segment.
On the “plot versus distance” version of the “elevation” screen, from
left to right, the “active logs” with the lowest numbers are illustrated first,
followed by the “active logs” with the highest numbers (e.g. “ACTIVE LOG”,
followed by “ACTIVE LOG 001”, followed by “ACTIVE LOG 002”, etc.) When all the “active logs” have been
generated internally by the GPS, this means that the “plot versus distance” and
“plot versus time” elevation screens will run in chronological order (oldest to
newest) from left to right, but when “active logs” have been uploaded from
MapSource, this is no longer the case, since a newly uploaded track will appear
on the right side of the “plot versus distance” and “plot versus time”
elevation screens, even if it represents very old data. If the same “active log” is uploaded
multiple times from MapSource, it will appear multiple times on the “plot
versus distance” and “plot versus time” elevation screens. All in all, the Etrex Vista is not really
designed to deal well with “active logs” that are uploaded from MapSource to the
GPS. In fact, when “active logs” are
uploaded from MapSource to the GPS in a non-chronological order, and then
viewed with the GPS’s “plot versus time” elevation screen, sometimes this
causes the GPS to crash. (When I’ve
experienced this, I’ve always been able to restart the GPS with no problems,
and with no lost data.) For the best
chance of trouble-free operation, the best policy may be to use the “clear”
option after uploading data from MapSource to the GPS, so that none of the
“active log” segments that might have been uploaded from MapSource will linger
in the active log memory area. (If
desired, the “save” menu option can first be used to save these “active log”
segments as “saved tracks”, and then the “clear” menu option can be used to
empty the “active log” memory area.)
However, as of this writing, I’ve never had any problems that seemed to
be related to “active logs” that were loaded from MapSource to the GPS in a
non-chronological order, except while I was actively scrolling the “plot versus
time” version of the elevation screen. Therefore I don’t think that this
problem would arise during flight.
We’ve noted that
when data is uploaded from MapSource to the Etrex Vista, any segment that does
not begin with the name “active log” (not case-sensitive) is uploaded as a
“saved track” rather than an “active log”.
As a “saved track” is uploaded, its name will appear on the “saved
tracks” screen, and the “tracks log” memory indicator will not show an increase
in the amount of the “tracks log” memory that is currently in use. The segment
will not appear on the “plot versus distance” or “plot versus time” page of the
elevation screen. The segment will not
be visible in the “breadcrumb trail” that represents the cumulative total of
all the “active logs” in memory. All
this is characteristic of how the Etrex Vista handles any “saved track”,
regardless of whether it is created internally by the GPS or uploaded from
MapSource. Like all other “saved
tracks”, the uploaded ”saved track” will not contain any time-related or
date-related information, even if time-related and date-related information was
present when the segment resided in MapSource.
(This situation could arise if the segment was originally an “active
log”, whose name was then changed so that it no longer began with the words
“active log”, which would then turn the segment into a “saved track” as far as
the Etrex Vista is concerned.) The
Etrex Vista handles “saved tracks” uploaded from MapSource without any
problems, just as if they had been generated internally rather than
uploaded. If the name of the “saved
track” was longer than 13 characters when it resided it MapSource, it will be
truncated at 13 characters after transfer to the Etrex Vista, and lower case
letters in the name will be converted to capital letters.
We’ve mentioned
that the maximum number of points can be incorporated into a “saved track” is
750. If the user attempts to upload a
longer “saved track” from MapSource to the GPS, a “track truncated” message
will appear on the screen of the GPS after the first 750 points are
transferred. However, “active logs” can
be much longer than 750 points. If the
user wants to transfer a “saved track” that is longer than 750 points (perhaps
because it has been made from several “saved tracks” that have been spliced
together in MapSource) from MapSource to the GPS, here’s a handy trick. First, “clear” the GPS’s “active log” memory
by using the “clear” button on the “tracks” menu screen. Then in MapSource, change the name of the
segment of interest from the “saved track” format to the “active log” format
(e.g. simply “active log”.) Then
transfer the segment over to the GPS.
Naturally, the segment will transfer as an “active log” rather than a
“saved track”. Once the segment has been
transferred to the “active log” memory of the GPS, press the “save” option on
the GPS’s “tracks” menu screen to create a “saved track”. Choose the “save entire log” option. The resulting “saved track” will represent a
subsample of the track points from the newly transferred “active log”, and
though the full length of the segment will be present with no truncation at the
end, the segment will be comprised of no more than 750 track points. As noted above, it might be wise to use the
“save” option to clear the “active log” memory area again at the end of this
procedure.
23) Additional
notes on MapSource 6.9.1
We’ve referred to
MapSource frequently above. In all
cases the specific version of interest was MapSource 6.9.1.
I now always save
MapSource files as “Garmin GPS Database Version 2 (*.gdb)”, which is the latest
file version offered by MapSource 6.9.1.
I’m not familiar with the differences between files of this type, and
the two earlier file versions also offered as “save” options by MapSource 6.9.1. These 2 earlier file versions are “Garmin
GPS Database Version 1 (*.gdb)”, and “MPS Files (*.mps)”. I used the *.mps file version in the past
with an older version of MapSource, and haven’t had any problems re-saving
these older files as the newer Version 2 (*.gdb) files, nor have I noticed that
this has created any changes in the files.
Here are a few
additional tips on the MapSource program:
When data is
being transferred from a GPS to the MapSource computer program, and the
computer involved is running on an external power supply rather than on
internal batteries, a momentary interruption of power to the computer will
cause the transfer to fail. Before
resuming the transfer, the GPS should be turned off and then back on; otherwise
the subsequent transfer will also fail.
When there is a high risk that the computer’s power supply will be
momentarily interrupted (e.g. when running off an inverter in a car) it’s often
best to disconnect the power supply before beginning the transfer of data.
When viewing
downloaded GPS data in MapSource, if the file contains a large number of
waypoints, the identifying labels for the waypoints may obscure most of the
other information on the map screen, including the downloaded tracks. An easy way to make all the waypoints
disappear is to go to the box labeled “show waypoints in category...”, and
enter a category for which there are no waypoints (e.g. “Category 16”.)
In MapSource, if
you right-click on a track or waypoint or route on the left side of the screen,
that feature will be highlighted in yellow on the map. However, that feature may lie beyond the
borders of the map, in which case it will not be visible. If you go to the left side of the screen and
left-click on a waypoint or track or route, or a group of multiple waypoints or
multiple tracks or multiple routes, and then choose the “show on map” option,
the map will automatically switch to a view that is centered around the
selected features, and will automatically change to a scale that will show all
the selected features in their entirety.
The same thing happens when you select the “show on map” button on the
“track properties” screen or the “waypoint properties” screen.
On MapSource’s
map screen, if you place the arrow pointer on particular track segment, and
then right-click on that point, and then select the “track properties” option,
the “track properties” screen will appear.
The “track properties” screen is a list of every track point in a given
track. The track segment on which
you’ve right-clicked will be highlighted on the “track properties” screen. This is a handy way to find the altitude or
lat/lon associated with a given point on a track. If available—i.e. if the track originated as an “active log”
rather than a “saved track”—the “track properties” screen will also show the
speed at that particular point in the track.
On MapSource’s
“track properties” screen, if you click on a particular track point or group of
track points, that track point or group of track points will be highlighted on
the map screen. (As long as the “track
properties” screen is open, unfortunately you won’t be able to manipulate any
other screens, but you can move the “track properties” screen to one side to
get a view of the other screens.) If
the “center map on selected item(s)” box is checked, the map will move to
center around the selected items. If
you click on the “show on map” button on the “track properties” screen, the map
screen will automatically change to a scale that shows the entire track that is
being featured on the “track properties” screen. This is not always desirable—avoid clicking on the “show on map”
button on the track properties screen if you want to keep the map zoomed in to
scale that is too large to show the entire track in question. When you click on a particular track point
on the “track properties” screen, sometimes the highlighted track point will be
lost amidst the clutter on the map.
Choosing the “center map on selecting item(s)” box and then zooming the
map in will reveal the highlighted track point. However, you’ll have to close the “track properties” screen
before you can zoom the map in. After
zooming the map in, you can easily bring up the “track properties” screen
again, as described above.
As noted above,
often several tracks will lie on top of each other. Typically one will originate from an “active log” and one or more
others will originate from a “saved track”.
In this case it can be helpful to make a copy of the MapSource file and
delete all the “saved tracks” from that copy, so that only the “active logs”
remain. This allows you to easily click
on a track and bring up the “track properties” screen for the associated
“active log”, rather than accidentally bringing up the “track properties”
screen for a “saved track”, which contains less information (fewer track points
and no time, date, or speed information.)
On MapSource’s
“track properties” screen, the “show profile” button brings up a graph of
altitude versus time. There’s no easy
way to pick a point on this altitude profile and highlight it on the “track
properties” screen or on the map. By
scanning through the altitude information on the “track properties”, it’s
possible to find the track points associated with altitude peaks, and then
locate these points on the map.
In MapSource,
individual waypoints or sets of waypoints can be cut, copied, or pasted from
one file to another. One very handy
feature is the ability to select waypoints or tracks or routes or maps with the
pointer tool on the map, rather than from the alphabetical lists of waypoints,
tracks, and routes. To do this, first
make sure that the desired category (maps, waypoints, routes, or tracks) is “on
top” of the other categories on the left side of the screen. Then click on the pointer tool (the icon
looks like an arrow), and draw a box around the area of interest on the map.
All the waypoints, routes, and tracks in the area of interest will be
highlighted in yellow on the map. (More
precisely, the entire length of all the routes and tracks that pass though the
area of interest will be highlighted in yellow on the map, along with all the
waypoints that lie in the area of interest.)
Then go to the left side of the screen.
You can left-click on the “up” and “down” arrows to scroll up or down
through the list of whichever feature is “on top” (waypoints, routes, or
tracks), but don’t try to click on the index tabs to change which feature is on
top, or you’ll have to start over.
We’ll assume now that “waypoints” are on top; if “routes” or “tracks” are
“on top” a similar procedure will apply.
When you find one of the waypoints that lies within the block of area
that you’ve outlined on the map, it will be highlighted in light purple. All the other waypoints that lie within the
box you’ve outlined on the map are also highlighted in purple, though they may
not be all visible at once on the left side of the screen. On the left side of the screen, right-click
on any of these highlighted waypoints (being careful not to accidentally click
on any waypoint that is not highlighted) and you’ll get a menu of options that
includes “cut”, “copy”, “paste”, and “delete”.
Whichever option you choose will be applied to all the highlighted
waypoints, i.e. to all the waypoints that lie within the block that you’ve outlined
on the map. This is a very good way to
quickly choose all the waypoints that lie within one particular geographic
region.
24) Additional links
For more GPS-related information, see the following articles on
the Aeroexperiments website:
"Using a GPS in
soaring flight"
"Notes on the
glide ratio functions of some Garmin GPS receivers with pressure sensors,
including the GPSmap 76S/CS/CSX, GPSmap 60CS/CSX, and Etrex Vista/Vista C/Cx"
“Map screen size
comparison of some handheld Garmin GPS units with numerical data fields
enabled: GPSmap 76S, GPSmap 76C series, GPSmap 60 series, and Etrex series”
"Notes on the Garmin GPSmap 76S"
"Notes on the Garmin Etrex Vista"
