I'm trying to combine two rasters to create a more accurate DEM for some viewshed analysis I need to run- I've got a raster showing building heights and I've got a DTM raster (sourced from OS data). I need to add the values of the building heights to the DTM so that the final results appear with the height of the ground PLUS the height of the buildings.
I've tried the raster calculator, and also the SAGA mosaick tool but neither is producing what I need. What can I do?