5th Comparson of Garmin 60c and Magellan SporTrak Pro (STP)

(Toto, I have a feeling we're not in [Olathe] Kansas anymore…)

The trip was south of Red Rock Canyon National Conservation Area, west of Las Vegas, Necada.

This Topozone map shows the approximate area. On this trip, we looped west from highway 159, up the ridge, then south, then back east through a deep canyon to route 159.

Look here for photos of the topography.

The aim was to see how both GPSRs fared, during a mix of open ridge climbing and occasional ascents and descents through partly closed chimneys. I was particularly interested in how the 60c and STP handled track records when part of the sky was blocked for periods from 10 seconds to 20 minutes. Often I depend on my track for navigation back down from a summit, and I am interested in finding exact ascent routes and avoiding dry falls.

In the three maps below, the STP track in blue, and the 60c track is in red. Click each map thumbnail to see the full-sized image. These are "raw" tracks. The STP was set on "auto, detailed" for the track log, and the 60c was set on "normal." WAAS was on for both. I placed the 60c in an external net pocket high on the back of the pack, to protect it from scratches, and placed the STP on my right front packstrap, high up near my neck.

North is up; scale bar on 1st map.

At left is the STP track only, with the bold black numbers 1-4 denoting several areas of interest.

1) This trebling of the STP track is real. I went left of the main group, to explore a possible route up a chimney; the route was totally enclosed at one point, and I had to "spin" around on my vertical axis several times, before I turned back.

2) This jag artifact, which does not appear in the 60c log (next map), was possibly due to the GPS positions. I faced into a shallow, narrow chimney for some time; the STP was deeper in the chimney, and was blocked by my body and the rock. The 60c was on my back, facing out of the chimney.

3) This doubling appears on both logs, and is real; I made two trips to guide people up a slot. The 60c is more realistic, putting the traces close together (next map).

4) The tracks in the deep canyon are not likely to be accurate; the WAAS was certainly nonsensical.

A comparison of the 60c and STP tracks. The 60c lost sync 13 times and generated 14 logs. Often the first point recorded to the log, after sync was regained, was wildly inaccurate; if those first points are eliminated, the 60c track is more consistent with the STP track. Unfortunately, the wild points show up on the track, on the LCD screen, and can be difficult to interpret in the field. On the ridge, the 60c recorded the details of climbing routes, while the STP averaged out small zigs and zags.

A detail of the area around number 1 in the first map, on an aerial photo. I traveled up this steep E-W valley fairly fast; the STP was apparently content to dead-reckon in places of poor reception, whereas the 60c generated several track logs, each with an initially wild guess.

Summary: I wish there were a way to make the 60c use more discretion in recording the first track point, after loss of sync. The wild guesses are not useful in rough terrain, and make the track hard to interpret during descent. Otherwise, the 60c seems more accurate on the open ridges, and gives a truer reflection of decisions made during the climb, than the "constantly averaging" STP.