GDALers: We're trying to figure out a good algorithm for computing topographic slope for Alaska, which is both huge and near the pole. Our DEM is currently in geographic coordinates, but we need slope over a fixed distance (change in elevation vs. horizontal meters). The issue is, there is no projection to switch this to to get an accurate set of slope calculations. Of course with degrees, the X and Y distances change over the globe -- so the horizontal distances will be variables from one window to the next. I have seen various solutions published, but I wanted to see if someone knows of a decent coded-up algorithm for this. Thoughts?
Some background: http://gis.stackexchange.com/questions/14750/how-to-use-srtm-global-dem-for-slope-calculation/40464#40464
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