[GRASS-dev] r.cog module for center of gravity and planar trend

[Hamish]

Hamish wrote:
> The module will also allow you to calculate the average
> azimuth and dip angle of the 2.5D raster surface, and
> optionally use that information, together with the above pivot
> point, to create a new planar-trend raster surface generalizing
> the DEM using the r.plane module.
...
> There's a bug in the dip angle method though, in so far as I
> haven't figured out the best way to calculate that yet.

ok, I've improved on the previous method a bit, but it's still
not right.

the latest idea to get the overall trend dip angle is to take the
slope map, and for each cell do some trig using tan(slope) angle
and the cell width to find a dz. Then use r.univar to sum up all
of the dz to find the residual overall "z", then use the atan()
to get back to an angle. But the result is still off.

I'm not sure about the cell-width part, I just used nsres() but
maybe that should be lengthened (up to a max of res*sqrt(2)) based
on the overall or local azimuth? or as the magnitude of sqtr(dx^2
+ dy^2), or ...?

any ideas?


thanks,
Hamish