This is somewhat related to a previous question I asked: What Algorithm is used by ArcGIS Watershed tool?
I was wondering if there is a more efficient way to calculate catchment areas if you are interested only in the polygon defining the catchment area (rather than all cells contributing to the catchment area). Doing a recursive search seems very expensive and would return a lot of information we don't want (namely each cell within the area).
Assuming the same starting point - a raster grid and a pour point/outlet (I leave it open for now whether the raster is a DEM, Flow Direction or Flow Accumulation).
My first thought was to simply follow the 'steepest path' upstream of the outlet point, which would quickly take us to the 'edge'. But I could not think of a way to follow the 'edge' around.
Are there any other possibilities?
interested only in the polygon defining the catchment area (rather than all cells contributing to the catchment area)
Can you expand on the difference between these two? I do not think that there is a difference. – Devdatta Tengshe Jan 28 '14 at 8:51