Calculating area of a sloping surface

Does anyone have experience or tips when calculating the true area of a sloping surface?

The ‘footprint’ of a sloping area as seen directly from above (e.g. from a satellite), will be less then the true area.

I want to calculate the true area of grid. I guess this process needs to be on cell-by-cell basis, calculating the slope, multiplying the footprint with the slope factor summing up to get the total.

I agred. I would try:

  1. gdrmath AREA to calculate the “flat” area
  2. grdgradient -S to get the slope grid
  3. grdmath to get the real area from the previous two grids.
  4. grdmath SUM? to get the total. Or maybe trough grd2xyz.

This seems to be a good workflow; I’ll try it!

Thanks @Esteban82!

Maybe you could look as the following youtube video and the references within):


Thanks for sharing @Esteban82! Very interesting.

So this should have a limited effect, except if you have ‘many and steep mountains’.