On Wednesday 08 July 2009, Nikos Alexandris wrote: > On Wed, 2009-07-08 at 09:51 -0700, Dylan Beaudette wrote: > > On Wednesday 08 July 2009, Nikos Alexandris wrote: > > > There is something strange with the values though (they expand from min > > > = -32687 max = 32645). Don't have the time to dig further, maybe there > > > are details in the meta-data about it (!?). > > > > This looks like an overflow problem. Could it be that this file contains > > unsigned 16 / 32 bit integers, but is being read in as signed 16 bit > > integers? > > Probably you are right Dylan. In the meta-data it is written: > > << Level 2 DEM: Level 2 DEMs may contain void areas due to interruptions > to contours in the source graphic or DLG. Void area elevation grid posts > are assigned the value of -32,767. >> > > * This means that original data are for sure Signed (probably > Int16-bit... ?). > > * gdal reads the data correctly (look previous post of mine) as: > Band 1 Block=20x4 Type=Int16, ColorInterp=Undefined > Min=0.000 Max=1371.000 > NoData Value=-32768 > > * grass reports the range of the imported data as: > r.info dem250 -tr > min=-32687 > max=32645 > datatype=CELL > > * The data show up correctly in GRASS: > > g.region rast=dem250 && r.colors dem250 color=terrain && d.mon x0 && > d.rast dem250 > > > If we accept min=-32687 that was assigned to be nodata, what is this > max=32645? > > Nikos
Hi Nikos, Looks like a 16bit signed integer file. I have found that in the past using gdal_translate and manually setting the data type and nodata value results in the generation of a new file that GRASS can read in without further work. Also, have you tried manually setting NULL cells with r.null setnull=32768 Sometimes GRASS isn't notified of the nodata upon importing... Dylan -- Dylan Beaudette Soil Resource Laboratory http://casoilresource.lawr.ucdavis.edu/ University of California at Davis 530.754.7341 _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
