[GRASS-stats] Raster maps from GRASS to R and back to GRASS?

[Nikos Alexandris]

Nikos:
> >> But why is "NODATA=" set to 999? It's a bug, right?
> > Hmmm... one last thing: I see that it works properly only if some
> > out-of-range value is assigned to "NODATA=" (e.g. NODATA=-9999), right?
> > Setting NODATA=NULL is nonsense I guess.


Roger:
> No, not nonsense. It is a default like any other. Working out what is in 
> range is not easy - it is based on r.info -r, but has to take edge cases 
> into account. The current "buglet" - the bug is the user not specifying 
> NODATA manually -

:D

> was that in using parseGRASS in very recent releases, 
> one further layer of string to numeric conversion was needed to avoid the 
> value being set to 999 when the min and max values from r.info -r were not 
> "seen" as numeric.

> There have been several similar 999 problems before, all can be avoided by 
> setting the NODATA= argument manually. For these bands, setting it 
> negative will always be OK, and setting manually also saves time, because 
> the heuristic doesn't have to be used. In general, NODATA= will simply 
> handle the NULL values correctly - the problem with any non-null value 
> given is that it may actually occur in the data in the current region.

> Check out the CVS source from sourceforge - project r-spatial, module 
> spgrass6, it will work with your data.

Thanks for your efforts Roger. I think I have to postpone for now
trying-out the latest source code (or maybe I'll try it out tonight).

I would like to note that I skimmed several times through "Applied
Spatial Data Analysis with R" [1] but I did not find any concrete
comment about the "NODATA=" option. Maybe I wasn't careful enough...

Kindest regards, Nikos
---
[1] Applied Spatial Data Analysis with R, Series: Use R
Bivand, Roger S., Pebesma, Edzer J., Gómez-Rubio, Virgilio

2008, XIV, 378 p., Softcover
ISBN: 978-0-387-78170-9