On Wed, 22 Apr 2009, Nikos Alexandris wrote:
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...
Right, there isn't anything in the GRASS book either, where the interface
is described in more detail. In fact, the use of rgdal is quite recent, so
most of this implementation post-dates both sources.
Roger
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
--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [email protected]
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