[GRASS-dev] how to reproject a raster map with absolute numbers without losing data

[Glynn Clements]

Moritz Lennert wrote:

> > For anything other than lat-lon locations, G_area_of_cell_at_row()
> > assumes that the area of a cell is constant over the region. That's
> > true for equal-area projections, and not far off for small scales
> > (where projection would be almost an affine transformation), but it
> > could be quite far off at larger scales.
> 
> Do I understand correctly that you would like the function to return
> geodesic area in projected locations? That would be a nice feature,
> but I wouldn't make it the default. I think most people would expect
> constant pixel area in such location, knowing (at least some) that
> there is inherent error in the projection.

I'm not suggesting that G_area_of_cell_at_row() should be changed, nor
the new r.mapcalc area() function. Calculating the actual area based
upon the projection is computationally expensive.and rarely necessary.

I'm just suggesting that it might be useful if there was some way to
get that information, other than by creating maps containing latitude
and longitude values, projecting those with r.proj, then using
r.mapcalc to calculate the area (or other properties) of each cell
based upon those.

-- 
Glynn Clements <glynn at gclements.plus.com>