[GRASS5] [bug #859] (grass) raster data at lower resolution: no resampling...

Glynn Clements glynn.clements at virgin.net
Mon Nov 26 18:56:31 EST 2001

Request Tracker wrote:

> (sorry to be so chatty)
> from the GRASS prog's manual I understand that raster data
> are resampled on the fly when looking at them in lower resolution.

Yes. Note: "resampled" does not imply "interpolated"; you can't
meaningfully interpolate category values.

> I have tested this and found, that the maximum value is used
> instead...

Incorrect. When rescaling 2:1, the lower-right cell of each 2x2 block
will be used.

 that's wrong in my opinion.
> An example
> #use g.region to select a 6x6 subregion, say, at 30m resolution
> g.region
> #calculate a test map
> r.mapcalc test="row() + col()"

Try a different example:

  r.mapcalc test="14 - row() - col()"

This "flips" the output diagonally, so the values decrease from
top-left to bottom-right. This time, the resampled version gets the
minimum value.

> The last years I thought that the programmer's manual is right.
> Obviously not (or not any more).

To which part of the manual are you referring?

Glynn Clements <glynn.clements at virgin.net>

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