[GRASS-dev] r.in.gdal: add scale and shift parameters?

Markus Neteler neteler at osgeo.org
Sun May 22 03:09:41 PDT 2016

On Sat, May 21, 2016 at 7:45 AM, Glynn Clements
<glynn at gclements.plus.com> wrote:
> Markus Neteler wrote:
>> sometimes it is convenient to scale/shift input maps on the fly during
>> the import in order to avoid an extra step with r.mapcalc (think: tons
>> of scaled Landsat data etc).
> Perhaps a better option (albeit one which requires some amount of
> design, rathern than just coding) would be to have this performed
> during read, i.e. similarly to how reclass maps are handled.
> This would allow it to be used with r.external maps without needing to
> make a copy (which largely defeats the point of using r.external).
> It would also allow most maps to be stored as CELL, with better
> precision than FCELL (32 bits rather than 24) and less space than
> DCELL. It's quite rare for physical measurements to be sufficiently
> accurate that 32 bits isn't enough.

The latter idea, to store all data as CELL and the derive the
different representations from that I quite like.

As an example: Temperature data are often shipped as e.g. degree
Celsius * 10 or degree Celsius * 100. While I prefer to continue in
GRASS with Celsius (hence divide by the respective value) it is a
waste of disk space to then make all subsequent maps e.g. DCELL since
that precision isn't there anyway available from the original data.

As soon as 7.2.svn is branched off, we could consider to implement
such a change in trunk and publish it later as 7.4 or even 8.


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