[GRASS-user] [GRASSLIST:1160] RE: Surface area of a DEM

[Hamish]

Jonathan Greenberg wrote:

> I was thinking this, but does the fact that a DEM grid cell is square
> cause complications in this formulation?  A 45 degree slope to the
> west would have a different surface area than a 45 degree slope to the
> southwest.  I've come across some solutions that use a set of 8
> triangles created by the lines between the center cell and each of its
> 8 neighbors to help in the calculation, but I was hoping this ability
> might be buried in a GRASS command someplace.


think of each cell as a spinning dinner plate on a stick.

you can rotate each cell in the direction of the aspect, and the
slope->projected area will be the same.

dx*dy is its own entity, or if you prefer, the r.mapcalc command doesn't
know about the aspect.

??

Hamish