Digital pathfinding

December 1, 2007 9:35 AM

Is it possible to take a Digital Elevation Model of my favorite wilderness area and using OS X run some slope calculations in order to find new hike-able paths though an otherwise treacherous terrain?

I did a somewhat similar analysis back in my PC days, but have not played with OS X options. Basically I want to take a DEM and tell the software to black out any part of the map that has a gradient of over X degrees... In other words, show me what areas are too steep to hike. I could then find the "safe zones" and translate them in to GPS paths in order to be able to see more of my beloved wilderness area. (Richland Creek Wilderness Area - Arkansas)

What software should I use on OS X to do this? (and how?)
Would the resulting analysis be reliable enough when I actually have boots on the ground?

posted by jlowen to sports, hobbies, & recreation (8 comments total)

The reliability of the analysis will depend entirely on the resolution of your DEM. Unless there is really good data for the area you are interested in, it might not show things like 10m high cliffs. It depends what you mean by reliable enough. Reliable enough to navigate by in heavy fog? Reliable enough to give you a vague idea were you may or may not want to hike?
posted by ssg at 10:02 AM on December 1, 2007

I would say "reliable enough to point out new paths to try". I certainly have enough brains not to rely upon experiments for any serious survival/navigation scenarios.

Case in point, I know this area well and know the three or four favorite spots very well. Unfortunately because of terrain I have never been able to connect my three favorite spots into one hike. Its usually drive to parking spot 1, hike 3 miles to point a. Return to car, drive to parking spot 2, hike 2 miles to point b.

Point A and B are actually very close, but previously unconnectable due to some cliffs. I KNOW there has to be another way to connect them in one hike without using the car.

I found this example of how to do it on PC - I am looking for MAC solutions.
posted by jlowen at 10:13 AM on December 1, 2007

Remote sensing software for Macs is described here. However, I can't find a direct link to a download site.
posted by desjardins at 11:28 AM on December 1, 2007

That page is an instruction manual released in 1998 for a PC program called Map Factory released by Thinkspace (now Keigan.) I doubt you will have any success obtaining this program which is more than 10 years old.

Google search on 'GIS Macintosh' revealed this page of links as well as some others. Some of these programs accept DEM files but since I don't do this kind of thing I can't say how flexible or useful they are. Good luck finding what you need!
posted by ikkyu2 at 11:31 AM on December 1, 2007

ERDAS Imagine and IDRISI are the most popular version of remote sensing products AFAIK, they'll both definitely do what you want, but I dunno if they run on a mac and I'm too lazy to read thru the links. There is some opensource remote sensing software out there IIRC but I don't remember what it's called (or if it runs on macs).

Why not just get parallels and XP, and then run whatever you want on your mac?
posted by desjardins at 11:42 AM on December 1, 2007

Perhaps you've got better DEM's then I've got, but my experience is that features too small to show up on DEM's can make it hard to traverse an area -- I wouldn't discourage you from trying what you're doing, but I wouldn't promise that it would work either.
posted by devonianfarm at 3:29 PM on December 1, 2007

I concur with the folks who are pointing out the problems with most DEMs. They just don't have the resolution to perform the analysis you're looking for. Unless you have LIDAR quality elevation data, you're unlikely to be able to get the vertical resolution required. Your best bet might be scouring high resolution (sub 1 foot) aerial photos for potential paths that you can assess using your personal knowledge of the area. Collecting GPS data the next time you're hiking hiking there might assist you in discerning potential paths as well, if you can overlay it with the aerial photos.
posted by mollweide at 8:24 PM on December 1, 2007

If you are highly motivated, there was a section in Mapping Hacks by ORA about using GRASS to do terrain analysis. GRASS is available for OS X, and a new version was just released a few days ago. It is very much command-line software, however, and using it to do what you want will require some perseverance.

Arkansas' geodata warehouse might have some LiDAR data for you to play with if you can get through its interface to find it. Some google searching referred to the Arkansas River LiDAR Project, which might have coverage of the area you are interested in. If you can't find data on the website, it might be worth looking for an email on that site to ask a question or two.
posted by hobu at 9:26 PM on December 2, 2007