I would like to compute global topographic indices based on SRTM elevation data. These indices are computed along river/channel networks extracted from a DEM and are a functions of both local slope and upstream area obtained from a flow accumulation routine. For those that are familiar them, the indices I am interested in are a stream power and channel steepness index.
To compute these on a global grid (worldwide from ca. 60°N to 60°S) and to be able to compare slopes and areas in different regions of the world, I was thinking about using compromise projections such as a Dymaxion/Fuller map, which would limit both area and angle distortions. These would allow me to treat the earth as a whole and ease the processing. However I have a hard time getting a handle on the distortions these kind of projection induce and the associated uncertainty or bias in slope/area (I would be happy with less than a few percent).
Alternatives could be to split the map into small regions where UTM projections would provide good alternatives, but this would mean a more complicated workflow. Another alternative is to go for a conformal projection to get the slopes right and then run a flow accumulation routine that is weighted by a correction grid which would account for changes in area with changes in latitude.
Does anyone have comments or suggestions about these workflows?
As these global estimates are computationally intense I'd better think twice about the right projection to use.
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