[GRASS-dev] adding units and vertical datum metadata to raster maps

Hamish hamish_nospam at yahoo.com
Wed May 9 08:29:39 EDT 2007

> > I have hacked together the attached code to add units and vertical
> > datum metadata to raster maps. It still needs some cleanup before
> > going into CVS, but right now I am interested in comments on the
> > approach taken. [it works]

Paul Kelly wrote:
> I remember Helena saying something about wanting a module to be able
> to check what units an input raster map was in, so it could warn the
> user if there was a subtle error. But if the units are totally
> free-form then this is likely to be unreliable. I'm wondering if
> there is some kind of standard for specifying units in an ASCII text
> string, and if we should investigate this and add wrapper functions
> to these new functions that try to ensure the units are in a
> prescribed format where possible. Of course people could still put
> anything in using your functions directly, if they had special
> requirements. But perhaps the modules Helena identified as having a
> serious need for storing and checking units should have some higher
> level functions to do that for them?

units must be free form, as the possibilities are endless.
(for example I have many µg/l raster maps)

$ units
2084 units, 71 prefixes, 32 nonlinear units

modules like r.slope.aspect can set "units=degrees" if they want,
and modules like r.shaded.relief and NVIZ can check, e.g.,
 strcmp(tolower(units), "meters")
for hinting about scaling (Lat/Lon). I don't think it is practical to be
seriously checked, but it can be useful for hinting when available and
also for rendering d.legend and ps.map scale bar labels automatically.


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