[GRASS-dev] Re: [GRASS GIS] #73: r.out.gdal tiff output does not work

[Glynn Clements]

Markus Metz wrote:

> Considering this, rather use e.g. raster_min - 1 as default nodata value 
> for GDAL floating point datatypes?

If fabs(raster_min) is large, raster_min - 1 won't be exactly
representable, and may be rounded to raster_min. You would need to
subtract a value which depends upon the exponent.

Also, the input data may contain -DBL_MAX. For FCELL, if the map is
large enough, it's possible that *all* finite values occur in the
data.

The question is: is GDAL's no-data value allowed to be any FP value,
or must it be finite? I'm guessing that the GDAL documentation doesn't
say (similarly, I don't think it's documented whether GRASS
FCELL/DCELL values are allowed to be infinite).

Actually, this may depend upon the format. If a format supports FP,
the format's specification may dictate whether or not NaN and/or
inifinities are considered valid.

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