Hi, I stumbled over this "funny" behavior of the col() function of r.mapcalc (GRASS6.2 and GRASS6.4, both on Linux).
According to The Book, col() "returns current col of moving window". I assume that for each row of a given raster layer col() should provide the values 1,2,3,4,5, etc. as it travels through the row. To produce a map of repeating value sequences (for example the numbers 1 2 3 4 ) the module operator can be used on the col()-function: col() operator result 1 mod 4 = 1 2 mod 4 = 2 3 mod 4 = 3 4 mod 4 = 0 5 mod 4 = 1 6 mod 4 = 2 etc this approach was put into mapcalc. The "1 + " makes sure that the sequence runs from 1-4 not 0 - 3: r.mapcalc modulo="(1 + ( col() % 4 ) )" A map was produced in a Spearfish location (col() should operate independently from the projection). Here it comes: For some (strange ?)reason, there are "ripples" in the "1 - 4" sequence. Instead of going 1234 1234 1234 ad infinitum once in a while a number is omitted: 1234 1234 234 1234 134 etc. Has anybody come across this behavior before ? Is this a feature/good-thing ? The phenomenon can be reproduced by using the above mentioned r.mapcalc command, displaying the result as a cell values layer. 1234, 1234, ..., Peter -- Dr. Peter Löwe <peter.lo...@gmx.de> Jetzt 1 Monat kostenlos! GMX FreeDSL - Telefonanschluss + DSL für nur 17,95 Euro/mtl.!* http://dsl.gmx.de/?ac=OM.AD.PD003K11308T4569a _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user
