Hi all, I am trying to calculate path distance, using a vertical factor table (created by Nico Tripcevich based on Tobler's hiking function, discussed here http://forums.esri.com/Thread.asp?c=93&f=995&t=138683, among other places). I created a DEM from SRTM version 4. When I calculate path distance using the vertical factor table, then generate contours, I get fairly evenly-spaced lines that look more like Euclidean distances. This is mountainous terrain. One should not be able to travel as far in the same amount of time when climbing a mountain. In fact, Euclidean distance contours seem to be further from the source point, even in areas where there are mountains that I know take two to three hours to climb! In the past I've calculated path distance before using another DEM (an earlier version of SRTM). To try and diagnose the problem I snagged this earlier DEM, and calculated path distance from the same point feature on both DEM's for comparison. My problem is best illustrated in the two attached graphics. In the first graphic, the red contour lines represent what was generated with the earlier DEM, and is what I expect. The blue contours are my problem: that is what is produced doing the exact same calculation with this new DEM I've created. I am going mad trying to figure out what the problem is with this second DEM. I've been able to calculate slope with this newer DEM (see attached figure 2), as well as some other compound indices. But there appears to be something wrong with the DEM. Other analyses have looked okay, but the path distance does not. Just to illustrate the point further the image shows slope from the second, problematic, DEM, and the evenly spaced path distance contours (which make no sense given the terrain). I compared the two DEM's, which are of the same geographic area, and there seems to be a big difference in elevation (600 m). My plan is to go back and use the older DEM. But, I would like to know what the problem is with the newer DEM (assuming that's what it is). Any suggestions or feedback would be much, much appreciated! Sincerely, Margaret
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