I'm working on a DEM in the Arctic region (initially in a NAD83 coordinate system) and I projected it into a North Pole Stereographic Cartesian coordinate system to compute slope and aspect. Now, because of the distortions, slope and aspect have to be corrected.
I corrected the slope without much trouble (Using SRTM Global DEM for Slope calculation?) but I'm stuck with the aspect correction.
I carefully read the suggestion made in How to use SRTM Global DEM for Aspect calculation? to add the longitude of the location + 90 degrees to the computed aspect value but it doesn't work as expected in my case (some values are negative as far as -87 degrees). I am not sure that the person was speaking about the same polar projection I'm using (he spoke about a Northern Stereographic projection while I use a North Pole Stereographic with Greenwich as prime meridian: 0.0).
Here are the characteristics of the projection I use:
Prime Meridian Greenwich 0.0 False Northing 0.0 Central Meridian 0.0 False Easting 0.0 Linear Unit Meter 1.0 Latitude of Origin 90.0
After much trial and error, I am looking now for any general formula for this aspect correction, taking into account the characteristics of the projection I use (or any other projection if it exists).
I have tried the method mentioned in my comment and I still have doubts about the results. I still have an offset of more or less 70 degrees between the aspects produced using Mercator (which are correct) and the aspects produced with a North Pole projection which are corrected by subtracting the longitude and then adding or subtracting 360 if the obtained result is < 0 or > 360 respectively. Any further ideas welcome...