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.
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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’.