On Thu, Aug 23, 2012 at 10:35 AM, Johannes Radinger <[email protected]> wrote: > Hi, > > I have a GRASS raster map which contains small values (e.g 2.5e-15) among > others.
This is (dangerously) close to the IEEE limit of double precision floating point values. If GRASS tests for fp precision, it regards (absolute) values smaller than 1.0e-15 (GRASS_EPSILON) as zero. > When I try to update a attribute column (Type = Float) of a corresponding > point vector (using v.what.rast), all small values turn in "0". > Thus I am curious about the precision of the float values of a vector > file which is probably different from the precision of raster floats. What > are the smallest > number that get correctly updated by v.what.rast?? This might be related to > the capabilities > of the underlying db-connection. v.what.rast prints fp values with 10 decimal places. The equivalent issue has aready been fixed in d.what.rast, now also for v.what.rast in trunk r52857. For FCELL maps, it prints 7 decimal places, for DCELL maps it prints 15 decimal places. Printing means here that fp values are first converted to text, then uploaded to the attribute table. Markus M > > Some additional info: I am working on Ubuntu 12.04 whit GRASS 6.5SVN. My > point vector is > connected to an sqlite db - table (standard sqlite connection). > > Of course I thought about a work around (e.g. multiplication by a large > scalar). Any other suggestions? > > Best regards, > > Johannes > > _______________________________________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/grass-user > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
