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?