|These are the procedures I follow most of the time (not
rigorous) when gathering GPS track and waypoint data.
From Fall 2005 to ???:
I'm now recording trails with a Garmin GPSmap 76 (put in my
pocket or holster)
connected to an external antenna on top of a hat and with a Garmin
76S carried in my left hand and sometimes in my right hand. The
GPSmap 76S is hand held in front of
me (vertical of course), a bit below shoulder level (sometimes up high
when satellite view is poor) and generally not
close (not so far up and out that my arm gets tired). Both receivers'
record method is set to "Auto". The interval method is set
Often" on both receivers. The track log usually gets saved to a
the end of the day so a full track log at the end of the day is
fine. Waypoints are not averaged on the 76S so that the
altimeter's elevation is stored. Sometimes the waypoint is
averaged on the GPSmap 76.
From Summer 2004 to Fall 2005:
The same as below except the track
log interval of the GPS 76 is usually set to "Most Often". I save the active log to a PDA when it gets close to full.
From April 2003 to Summer 2004:
Not much has changed from the period below except that since
Garmin has increased the track log size of the GPSmap 76 to 10,000
points, I usually run it with the interval method set to "Most
Often". There is plenty of space available for any day hike I'm
likely to do. The GPS 76 still has the 2048 point limit so that
is adjusted depending on the length of the hike. Also the track
log interval might get changed during the hike. For instance I
might start with it set to "More Often" on the hike in then lower it to
"Less Often" on the hike back out to the car.
I'm now recording trails with a Garmin GPS 76 (put in my pocket or holster) connected to an external antenna on top of a hat and with a Garmin GPSmap 76 carried in my left hand and sometimes in my right hand. The GPSmap 76 is hand held in front of me (vertical of course), a bit below shoulder level and generally not too close (not so far up and out that my arm gets tired). Both receivers' tracklog record method is set to "Auto". If I think the hike is going to be a long, all day hike, I set the interval to "Least Often". If the hike is going to be a short hike (less than 6 - 7 miles) and I'm not going to record any roads, the interval method will be set to "Most Often". I might also set it to something in between (such as "Normal") erring toward the "Least" setting to make sure that I can record everything I want to during the day. The track log usually gets saved to a computer at the end of the day so a full track log at the end of the day is fine.
The marking sequence (for waypoints) might be:
While walking the trails I usually pause when the trail makes a significant change in direction. The pause usually lasts until the speed has dropped to zero. It takes about 4 to 5 seconds to drop to zero when signal reception is good. It takes a few seconds longer when signal reception gets worse. I'm less likely to pause when the receivers are set to "Most Often".
The versions are: GPSmap76 ver. 2.08 and GPS 76 ver. 2.08.
From January 2002 to December 2002:
Since January 2002 I've started using a Garmin GPS 76 too. Eventually I plan on "only" using two receivers but for now I'm using all three to learn their behavior. The routine has varied a bit but is similar to the above except the GPS 76 tends to get most of the averaging time and the 12XL doesn't get much averaging time. The Venture is always in my left hand and the GPS 76 is in my right hand most of the time. The GPS 76 has had some time in my pocket attached to an external antenna with the 12XL in my right hand with no external antenna.
Since about March 2002 I no longer do a reposition with the Venture (see below). Now I record the initial point and record another mark if the location value has wandered enough - about 15 feet or more. They'll be averaged together. This has tended to give a bit more weight to the marks by the Venture over that of the 12XL. More recently I've sometimes made a second mark with the 12XL to balance the weighting and also with the GPS 76.
The Venture was upgraded to version 2.31 in the Spring of 2002.
The marking sequence might be:
From August 2001 to January 2002:
Since August 2001 the Garmin 12XL has been used in the same manner as before (described below). In addition, a Garmin eTrex Venture has usually been used on day hikes simultaneously with the 12XL. If I need the storage capacity, I'll use one and then the other with an attempt to use the 12XL in difficult satellite reception areas (because of the external antenna) and the Venture in more open areas. I consider the average of the two tracks, one from the 12XL and one from the Venture and gathered at the same time, a "single track". So far the firmware version of the Venture has ranged from 2.26 to 2.29.
The Venture is hand held in front of me (horizontal of course), a bit below shoulder level and generally not too close (not so far up and out that my arm gets tired). The Venture's tracklog record method is set to "Auto" and the interval is set to "Least Often".
The Venture doesn't have the "average" location function. I have had the Venture record a location mark 50 meters away from the track log that it and the 12XL recorded and with an excellent view of the sky. Since late November 2001 to about March 2002, I tried to watch the distance of the current mark from the current location (for instance, while I'm entering the name). If this distance got above about 12-15 feet, I would use the reposition function to place it at the current value.
The marking sequence might be:
From May 2000 (When Selective Availability was turned off) to August 2001:
Most of the data was gathered with a Garmin 12XL with firmware version 4.58 connected to an external antenna . The antenna for the 12XL is mounted on top of a hat to get the best reception (so I don't block any satellites). The tracklog record method is set to "Auto". This method records a point when the actual course differs enough from the projected course so the GPSR attempts to produce the most precise track with the least amount of recorded points. Garmin's algorithm for "Auto" varies by GPSR model and firmware version.
To get a more accurate track when hiking with the 12XL, I generally pause about 10 to 25 seconds if the trail changes direction by about 90 to 180 degrees. If the trail changes direction by less than 90 degrees, I pause about 6 to 15 seconds and sometimes a bit less for small changes in direction. Another method I use is to wait until the speed indicator drops to zero for moderate changes in direction (about 20 to 50 deg.). The length of time paused will also vary depending on whether or not I'm in a hurry.
The purpose of the pause is to force the 12XL to place a trackpoint close to where I'm standing (at the corner). This helps prevent corners from being "cut off". It seems to be primarily a matter of getting Garmin's "auto" log algorithm to change direction at the current location (log it at the actual corner) in the 12XL. The Venture records often enough (or the algorithm is good enough) that I don't believe the pause is necessary. It also means that the Venture with twice the amount of track log memory can't store twice as many miles as the 12XL unless there aren't many turns.
For placing waypoints I usually wait for the speed to drop to
"mark" the location. The speed is often zero or close to it by
time I get the GPSR out of my pocket and in a position ready to do the
"mark". With the 12XL, I turn on the "average" location function and
a waypoint code. So the location is averaged over the time it
me to enter the code (name) - helps if the location is currently
because it's a noisy, difficult reception area. When the Venture
is also in use, the time to enter the name into the Venture is also
in the 12XL's averaging time. The primary intent of the average
is to help prevent momentary spurious marks. I may wait some
seconds before finalizing the mark, especially if the location
or the EPE is changing often.
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