[R-sig-Geo] Proper algorithms for computing slopes for global/polar DEMs?

Clint Bowman clint at ecy.wa.gov
Fri Feb 20 21:38:56 CET 2015


Have you thought about a Lambert Conformal projection?  I'd think you 
could adjust the projection parameters to get a pretty nice grid over 
Alaska.  I'm sure the mesoscale modelers at UA-Fairbanks have worked this 
out.

Clint

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On Fri, 20 Feb 2015, Jonathan Greenberg wrote:

> r-sig-geo'ers:
>
> 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
>
> --j
>
> 	[[alternative HTML version deleted]]
>
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