How to mask the images in GRASS

Question

I have MODIS NDVI images, which needs to be masked with VI_Quality. I am using GRASS software and executing GRASS commands using shell scripts. I need to perform raster calculation (multiplication) for NDVI images with the VI_Quality. I want to multiply ith NDVI image with the ith image of VI_Quality. I have used the following codes :

for file in $NDVIFILES;
do
r.mapcalc "$file = $NDVIFILES * $QAFILES;
done

i=1
for file in $NDVIFILES;
do
r.mapcalc "file $((i++)) = NDVIFILES $((i++)) * QAFILES $((i++))";
done

I am unable to do this raster multiplication in a loop. Please let me know the correct syntax to do this operation.

Thanks

Answer 1

Here's what I suggest:

g.mlist --q type=rast pattern-"*NDVI" mapset=shenkottah >> NDVIFILES

and a similar expression for the QAFILES This will leave you with two files on your disk, each containing a list of the raster map names. To verify, test with the sed expression:

sed -n "4p" NDVIFILES

Then you should be able to run a loop to read the raster names and do your mapcalc, something like:

for i in `seq 1 22`; do \
NDVI=`sed -n "${i}p" NDVIFILES`;
QA=`sed -n "${i}p" QAFILES`;
r.mapcalc new_${i} = $NDVI * $QA;
done