[GRASS-dev] r.mapcalc division by 0

Helena Mitasova hmitaso at unity.ncsu.edu
Sun Jan 21 00:27:44 EST 2007


I noticed that the man page for r.mapcalc gives confusing
information about division by 0. It says:

Division by 0 and modulus by 0 are acceptable and give a 0 result.

but later on:
Division by zero should result in NULL.

I tried it and the second is true (it results in NULL)

And then there is an example

To produce a binary representation of the raster map layer a so that  
category 0 remains 0 and all other categories become 1:
mask = a/a

but what you get is a map with 1 and NULL.

I assume these are leftovers from pre-NULL times?

Helena

Helena Mitasova
Dept. of Marine, Earth and Atm. Sciences
1125 Jordan Hall, NCSU Box 8208,
Raleigh NC 27695
http://skagit.meas.ncsu.edu/~helena/







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