Two r.mapcalc calculations return a much bigger raster cell size than the input raster

Question

I tried the following calculations with a GeoTiff sample, having a cell size of 25m:

1. Calculating the togographic exposure (TOPEX) and
2. estimating the mean topographic curvature

Both, the resulting raster data from calculation 1. and 2. have a raster cell size of approximately 765m. Even when I choose a 1m GeoTiff, the resulting raster has a cell size of 765m.

Obviously it doesn't depend on the calculation.

Could be the problem that the input file is not type of .dem, .adf or .asc??

Answer 1

Are you sure that you've set g.region correctly? You should ensure that your mapset resolution is set to the resolution you want, e.g. if you want to set it to 1 m :

g.region res=1 -p

You should then re-run your calculations with r.mapcalc.

Answer 2

Agree with the first answer, but want to add that you can run g.region raster=<input.raster.name> to set the region bounds and resolution to match the input raster. It's just as important to set the region bounds to the input maps as it is to set the resolution. If the region is much bigger than the input maps, GRASS will still treat the "empty" areas as if they had data, and the result will be very big raster files and very long calculation times. BTW, you can also check the -d flag if you are in PERMANENT, and that will set the default region to always be what you set it to. you can check your current region settings with g.region -p.