i am attempting a volume calculation using the route of 2 dems (upper and lower) and trying to subtract the difference.
workflow as follows: A. rasterise vector contours (v.to.rast.attr)
B. create 2 dems (r.surf.contour)
C-D. create and rasterise vector overlay (in prep for mask) (v.to.rast.attr)
this is where it goes undone:
E. create mask (r.mask) - mask the regions in 4 outside of the polygon(s) with a '0' null value and those inside the polygon with a '1' value (indicating the area to be processed).
F: calculate area (r.surf.area) G: calculate volume r.volume or r.topidx
F1: raster algebra (r.mapcalculator in grass) // raster calculator in qgis (demA - demB)
Is this an appropriate workflow or what would an appropriate workflow look like (with associated r./v/g. steps)?