[GRASS-user] scale error for each pixel

[Moritz Lennert]

On 20/11/17 21:20, Ken Mankoff wrote:
> Dear Helmut,
> 
> On 2017-11-02 at 07:17, Helmut Kudrnovsky <hellik at web.de> wrote:
>> Ken Mankoff wrote
>>> Does GRASS (or GDAL?, proj4?) have a function (or addon) to provide the
>>> scale error  for a given cell?
>>
>> AFAIR there is now an area function in r.mapcalc in GRASS trunk to calculate
>> the pixel area.
> 
> There is. I've just built GRASS 7.5. But the area() function just returns nsres*ewres for each cell, it does not consider projection errors.

You could run area() both in your projected location and in a lat-long 
location (preferably using a similar datum), although you would have to 
be careful in the definition of the resolution in each location. 
Comparing the output should give you a notion of projection error.

For visualization you might want to try the Indicatrix mapper Plugin in 
QGIS...

Moritz