Markus Metz wrote: > > 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.
2.5e-15 is close to the "epsilon" value for IEEE double precision. This just means that (1.0 + 2.5e-15) is only barely distinguishable from 1.0. It has no relevance to the representation of small numbers. A double can represent numbers as low as ~2.225e-308 with no loss of precision. If GRASS_EPSILON is being used to compare absolute (rather then relative) difference, that's a bug. -- Glynn Clements <[email protected]> _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
