i try to pre processing data for a hydrological modell. Now i need to generate a raster with a specific Extend of 8000 x 8000 meters with the Elevation of the river bottom, but only where the river bottom appears. So the other Cells of the raster should not get a value.
What i have until now is a Polygon of the River, a DEM of the Area and what i want to do is: Assign the DEM hight to a new raster wich have the same extend as the DEM (8000x800m) but only on the area where the polygon of the river is should the new raster shown values.
I try it with a fishnet and i get the values assign to the fishnet but only on every polygon of the fishnet not only where the river polygon appears.
thanks for helping