Glynn Clements pisze:
-2^31 (= 0x80000000 = -2147483648) is the null value for the CELL type, so you'll never see that value in a map.
The FP nulls are the all-ones bit patterns. These corresponds to NaN according to the IEEE-754 formats, although it isn't the "default" NaN pattern generated by most architectures (which is usually 7fc00000 or ffc00000 for float and 7ff8000000000000 or fff8000000000000 for double, i.e. an all-ones exponent, the top-bit of the mantissa set, and either sign). So far as arithmetic is concerned, any value with an all-ones exponent and a non-zero mantissa is treated as NaN. But the GRASS G_is_[fd]_null_value() functions only consider the all-ones bit pattern to be null. I intend to change this in 7.x so that all FP NaN values are treated as null. This will mean that code which can generate NaNs doesn't have to explicitly convert them to the GRASS null value.
These should go to "Raster data processing in GRASS GIS". As I don't really understand the part about floating point, I won't do it myself. Somebody more savvy please do, putting it some simpler words if possible.
Cheers, Maciek _______________________________________________ grass-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-dev
