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  1. #1
    Heavylegs
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    In Need of Advice

    Ok I need some advice on choosing an adequate GPS unit to create fairly detailed maps of our local trails. I understand this is not a simple subject. I was looking at the Garmin 62 series, but I am not sure if this unit is the right one for my cause. Just to make it clear I am not interested in using it for navigation to find my way around, or to track my rides, just a GPS unit to create trail maps that will provide everyone better vision for our trails not the inaccurate one we have now. Also has anyone used 3D mapping software like the one found at Topofusion.com. Is this technique worth the trouble?

  2. #2
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    First off, Topofusion isn't really 3D mapping software. Google Earth does 3D better. ArcScene/ArcGlobe are more powerful than Google Earth. But really 3D isn't terribly useful for mapping because vertical exaggeration can be modified to make it appear a lot more hilly than it really is. For mapping, it's better to have a regular top-down map view with an elevation profile of a given trail with minimal vertical exaggeration.

    Now, as for which GPS to use, there's no hard and fast rule. A 62 series model will work well for what you want. A few guys who do work near me use them. I use a Garmin Oregon 450 and it works pretty well, too. There are folks here on mtbr (who don't post in this forum much) who use a Google Nexus 7" tablet with an external GPS receiver for trail mapping. When you're mapping a trail to make actual maps (not just track yourself), what matters is that you understand what your device does well (and what it doesn't) and try to account for that.

    What I mean is this: GPS accuracy will fluctuate over time. Some of that based on satellite position in the sky. Some of it related to the weather, tree canopy, your position on a hillside, and how fast you're moving. If you have a GPS capable of averaging waypoints (basically collecting data at 1sec intervals and averaging all those points together, achieving a more accurate point), it is most accurate to base your data collection around these points. Collect averaged points at important single locations like intersections, landmarks, and trail features. They don't necessarily have to be spaced uniformly or anything, but the fewer large curves between them the more accurate your data will be. Also collect tracks as you walk between these points. If you are riding to collect data, you will have a lower point density (use 1sec recording intervals for track recording) and less accurate data. To really make sure, walk the trail multiple times to lay down several tracks. From there, you can use one of a couple methods to "average" them together. For one, Topofusion can do it automagically. The algorithm isn't perfect, though. It comes up short in dense, twisty networks of trails. In those cases, I will hand-draw a new file with an "average" of all of the tracks.

    Obviously, this kind of accuracy requires a lot of work. Depending on your project, it may or may not be worth it. I am currently mapping many trail systems in my area. I'd never finish them if I was relying on that level of accuracy for all of them. So I just go ride the trails I want to map. The data I get is still mostly good enough for what I'm doing. If I need more accurate data for anything, I can always go back and collect more data. When riding a trail, I still do try to cover it a couple of times at least. Sometimes I get this in a single visit. Sometimes it takes a couple visits.

    Another word on software - depending on what I'm doing, Topofusion may not be quite what I'm after. It does a lot of things well, but it's not designed to make an attractive map for printing. For that, I use a program called Quantum GIS (free), MapWindow GIS (free), or Manifold (I bought this). I also know ArcGIS, but do not have access to a copy right now. After making the map, I usually import it into a vector graphics program like Inkscape (free) to handle some of the visual elements.

  3. #3
    Heavylegs
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    I am glde you are one willing to answer this post, as I have notice and respect your advice. As for the Garmin 62 series of GPS do I really need the higher end models or will the simpler ones be fine, I believe the the 62st and 62stc come preloade with maps as well as more storage capacity that allow the ability to insert more waypoints, are these features benifical. Also spoke of your friend using a tablet with a seperate GPS unit. Where can I find this type of unit and does it hold any true advantage to the single GPS reciever?

  4. #4
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    You don't need the preloaded maps from Garmin. That is an extra unnecessary expense. One thing Topofusion does well is that it can load satellite imagery onto a Garmin with that capability. You can also load vector topos for free that come from GPSFileDepot - Free Custom Garmin Maps, Ximage hosting, tutorials, articles and more for your GPSr. All the maps you'll need, and gpsfiledepot even has instructions for making your own. The program GPX2IMG can also be useful, as it allows you to load trail networks you create onto your GPS as basemaps so you can view them.

    The additional memory on more expensive models can be useful, but it depends on how much you like to fill up your device. On my Oregon, I have not needed more than the memory that was included on the device. However, if I had a model that had a camera, I'd want all the memory I could get so I could also fit the photos on it. The ability to take geotagged photos can be helpful when scouting or when documenting maintenance needs.

    As for the tablet, he's not using anything special. Just a typical off-the-shelf 7" Android tablet that he can connect to a Bluetooth GPS receiver. Lots of options for either device. Its main advantages have to do with the fact that it's a more powerful computer instead of a more basic single-purpose device. You can run other potentially useful apps in the field beyond just any mapping apps you might use. Maybe you'll need some reference information, there are clinometer apps for measuring slope, you can get a data connection a couple of different ways to allow you to have internet connectivity in many places. A major limitation to this type of system would be battery life. The guy in the Trailbuilding forum who does this doesn't have problems with the way he uses his, but it would be possible depending on how you used the device to drain it quickly. You'd need to be judicious with use to maximize battery life. A dedicated GPS will have better battery life, and will not vary as much depending on use.

  5. #5
    Heavylegs
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    Thanks Natehawk, I am leaning towards the Garmin 62. It seems like it will work for what I need. One major feature I think pushed me in that direction is the fact that the Garmin is waterproof. This will allow me to do my mapping on rainy days and save the nice days for riding or building trails! Unless the cloud cover causes problems for the GPS recievers?

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