[GRASS-user] CHELSA climate data set

[Markus Neteler]

On Tue, Feb 7, 2017 at 3:32 PM, Markus Metz
<markus.metz.giswork at gmail.com> wrote:
[...]
> Compared to GMTED, CHELSA extents further south to 90:0:0.5S which conforms
> to the GMTED grid geometry. For CHELSA, however gdalinfo reports
> Pixel Size = (0.008333333300000,-0.008333333300000)
> while for GMTED, gdalinfo reports
> Pixel Size = (0.008333333333333,-0.008333333333333)
>
> The reason for the slightly smaller pixel size is most probably reduced
> floating point precision during creation of the CHELSA data.

from personal comm.:
They are currently investigating where the precision is cut in their
workflow (the upcoming V1.2 shall come with a related correction).

> Unfortunately it changes East from 179.9998611 to 179.9998597 and north
> from 83.9998611 to 83.9998604.
>
> The more serious problem is that GRASS can not handle ll coordinates like
> 180:0:0.50W or 90:0:0.5S.
>
> I have relaxed the ll restrictions in my local copy and can now import
> CHELSA and other for GRASS problematic ll datasets without getting e.g. a
> narrow N-S strip, or GRASS fixing a subtle rounding error that in fact is
> not an error. That means after each import I have to manually check if
> resolution and extents make sense, and if in doubt fix them with r.region.

That's probably rather more a power user task than common user
knowledge... Is there anything we could do at libgis level like
relaxing the ll restrictions along with appropriate user messages?
More and more global datasets are getting published, so the issue will
likely come up more frequently. Just to make it a bit easier :-)

markusN