[GRASS-dev] ascii export and import, large file problem

[Paul Kelly]

Hello Hamish
Thanks for bringing this up again. ISTR being too busy to reply straight 
away the last time and then forgetting...

On Wed, 18 Apr 2007, Hamish wrote:
[...]
> --relevant quotes--
> [1...]
> For a real y-axis label I think we need to add a new (optional) "units"
> element to the raster format (e.g. in cell_misc/).

OK this seems like a very good idea. Several times Helena has suggested 
the idea of adding "vertical datum" support to a location, but I was 
always quite negative about it in pointing out that there was not even 
any way of indicating that a particular raster map contained elevation 
data. But in fact, the obvious answer seems now to be that it should be 
done on a per-raster map basis rather than a per-location basis. I.e. if 
the metadata for a raster map indicates that it contains elevation data 
(i.e. units are a length measure) then there should also be a facility to 
specify the vertical datum the length measure is relative to.

> [2...]
>> The user should be able to add a title for the legend.
>
> For vlegends that's doable. For raster legends I hope to add
> G_set_raster_units() and G_get_raster_units() to write/read a simple
> string containing raster data units (set from "r.support units=") which
> will be stored in $MAPSET/cell_misc/$RASTERMAP/units. Raster legends and
> things like lat/lon NVIZ and r.shaded.relief could use the tag if it
> existed.
> --endquote--

I think it's worth putting enough thought in so that the feature is easily 
usable for more than just legend titles. Especially how to specify 
vertical datums. I suppose there are a few very standard ones, like WGS84 
ellipsoidal height and that kind of thing. Actually I think the EPSG 
co-ordinate system database also includes vertical datums. Maybe it has 
some kind of unique codes that we could re-use. Maybe we should have a 
vdatum.table file with descriptions. Or maybe we should just put a 
human-readable name in and leave it for manual interpretation.

I'm really not too sure.

Paul

>
>
> apparently cell_misc/ is evil, so that moves it to
> $MAPSET/units/$RASTERMAP until GRASS7  when it moves to
> $MAPSET/raster/$RASTERMAP/units
>
> I don't like to add another element dir to $MAPSET, but...
>
>
> Hamish
>
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