On Wed, 6 Mar 2013, Biuw, Martin wrote:
Hi,
I'm using readGDAL to read data from a geoTiff file. The valid data
range of the single band is -26 to 0. I have two versions of the file,
one with a NoDataValue = -9999 and one with NoDataValue = -128. When
reading the version with -9999 everything works great, and I get the
data values in band1 mapped correctly on the original interval. But when
I use the version of the file with NoDataValue = -128, these band1 data
values get re-mapped to 0-255.
This appears to indicate that the files do not only differ in NoDataValue,
but also in storage form. Does examining the output of GDALinfo() on both
tell you anything? Is one a signed 16-bit integer, the other Byte? Maybe
paste some of the output into a follow-up?
Roger
I remember reading a helpfile or R-sig
post on why the NoDataValue has such an effect, or what can be done to
get around it. But can't for the life of me find that message anymore.
The reason I need to use the file with NoDataValue = -128 is that this
is in UTM 35 while the other one is in UTM 33. Since it's a
SpatialGridDataFrames, I'd rather not use spTransform on it, since this
turns it into a SpatialPointsDataFrame. The files were originally
created (by someone else) in ArcGIS, so I could always ask them to
re-create them with correct NoDataValue. But maybe there's a way to
explicitly tell readGDAL how to treat the data values? I've desperately
been looking for any help on this, but must be looking in the wrong
place....
Thanks in advance,
Martin
________________________________________________________________
Martin Biuw (PhD)
Researcher
Norwegian Institute for Nature Research - NINA
Postal address: Framsenteret, 9296 Troms?, NORWAY
Delivery/Visiting address: Framsenteret, Hjalmar Johansens gate 14, 9007
Troms?, NORWAY
Phone: +47 77 75 04 17 * Cell: +47 40 72 96 15 * Fax: +47 77 75 04 01 *
www.nina.no<http://www.nina.no/>
________________________________________________________________
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--
Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: roger.biv...@nhh.no
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