Hiking tracklogs
 

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Naomi Peak
Waterfall Canyon
Frary Peak
Thurston Peak
Red Pine Lake
Ogden Canyon
Adams Canyon

E-Mail Jeff

While browsing through the GPS newsgroups, I often come across questions regarding the accuracy, and reception capability of GPS receivers. There are all sorts of great sites available where you can get information regarding controlled measurable data, but does this data always relate to how your receiver will perform in the field? You can also walk around with the different receivers in your hand, looking at the satellite signal strength bars while trying not to stumble, but I've found that doesn't always tell the whole story either. A different but helpful method of determining the reception ability of a GPSR is to download and view the tracklogs, looking for obvious positional errors, or places where the receiver lost reception. This method isn't the greatest for determining absolute accuracy, but when you hike out and back trails, it will give you a good idea of the repeatability of the receiver. If you overlay the tracklog on a good map, it's also often quite easy to determine if there were any significant positional errors. I've found the tracklogs tell a better story about field performance than what you can determine from the satellite status, EPE, and other informational pages on your GPSR.

As for the equipment I use, I've found the size, shape, and ease of use of the eTrex series works great for hiking. I have and use a basic yellow eTrex, and a Legend. Over the last couple years, I also occasionally took my GIII+ as a data logger, but discovered that while it gave the appearance of being more sensitive, I had a harder time recording accurate trail data with it. Part of the problem was a result of the shape, and size, which made it more awkward to carry in an optimal way. I also found that in certain areas the GIII+ was more susceptible to multipath reception problems. The eTrex also suffers from multipath, but the more directional nature of the antenna makes it easier for me to control. In order to get data as good as what I was getting from my eTrex's, I ended up having to use a Mighty mouse II antenna situated on top of my pack when I used the GIII+. I found this setup, while somewhat better, wasn't nearly as convenient for me as an eTrex on my shoulder, so I quit using it and went with the simplicity, small size, and lack of wires of the etrex. When I'm looking for the best possible tracks though, I do go with the GIII+ mighty mouse combination. In the fall of 2002, I added a sportrak map to my collection. It's the most accurate of the group for recording a fixed position, but has some quirks that make it not necessarily the greatest for recording tracks.

On the pages detailing each hike, you can download the tracks overlaid on a 1:24000 scale TOPO map created using ExpertGPS. I ended up making the maps rather large so that variations in the tracklogs would be more readily apparent. I then used a lot of jpg compression on the files. Unfortunately, despite the heavy compression, I ended up with some fairly big jpg files that can be slow to load, and will result in your having to scroll around a great deal to view the whole thing (Don't forget to expand the picture to full size if your browser automatically sizes to fit.) To allow you to pick and choose the maps you may want to view, they don't automatically download unless you click on the hyperlinks. You can also download the actual track data by right clicking on the hyperlink for the data, and using the save target data function on your browser. The tracklogs are in the TopoGrafix "Loc" format. You can download free software (easyGPS) to view the data at www.topografix.com,  alternatively you can download ExpertGPS from the same website, which is the program I used to produce the maps with.

What you'll find on each page:

The Naomi Peak page shows map trail data problems, and has tracklogs from both a basic eTrex carried on the hip, and a legend carried horizontally. The hip carried log shows the poor results you can expect from using the receiver in this way.

The Waterfall Canyon page has a error filled tracklog that resulted from carrying a Legend on the hip. You can also see some age related errors in USGS trail data.

The Frary Peak page shows a log from carrying the Legend horizontally on a trail up a mountain peak on an Island in the Great Salt Lake.

The Thurston Peak page displays problems with the tracklog of a basic eTrex carried on the belt where the legend on a pack strap ended up recording pretty decent tracklogs. It also shows trail data errors on the TOPO map.

The Red Pine Lake page shows tracklogs produced by a GIII+ and a Legend in an area where terrain caused reception problems. It's an area where although quite old, the USGS trail data appears to be pretty accurate.

The Ogden Canyon page shows tracklogs from the Sportrak, and Legend while geocaching in a tree filled canyon area. Both receivers set to auto normal mode.

The Adams Canyon page shows tracklogs from a Sportrak, and a Legend in a tough reception area. Legend set to auto normal, sportrak to Auto detailed.