I think this is a general enough question to apply to more than just gdal_calc, but perhaps not. When I run

gdal_calc.py -A map.tif --outfile=deforestation_00-10.tif --NoDataValue=0 --calc="A >= 7"

on a 38000 x 38000 62.5MB tif, the output is 1.37GB (and still 38000 x 38000). I feel like i'm probably missing something big here, i.e. how tif data is stored. [the same thing happens when I run it using the raster calculator in qGIS] Thanks in advance.

Bonus points--anyone know how to include and/or logic in the --calc="..." in order to evaluate the following: (map@1 >= 7 AND map@1 <= 9) OR ((map@1 >= 10 AND map@1 <= 12) * 2)

  • 2
    Are you aware that TIFF actually comprises multiple formats, including (but not requiring) compression? Because 38000 * 38000 / 2^30 = 1.35, it is clear the output is not compressed and the input is compressed. For an example of using Boolean operations in gdal_calc, please see this recent answer.
    – whuber
    Aug 22 '13 at 21:00
  • 3
    Your "bonus points" line should probably have been asked as a separate question - that helps keep things organized and easy to search.
    – Richard
    Aug 18 '14 at 22:08

Use the --co=creationoptions parameter to compress the output.

gdal_calc.py --co="COMPRESS=LZW" -A map.tif --outfile=deforestation_00-10.tif --NoDataValue=0 --calc="A >= 7"

For more compression options, see the GDAL GTiff format description.


Filesize question

If the result data is boolean True/False (or 1s and 0s), use --type=Byte with the creation option NBITS=1 to create a file with 1 bit per sample. This will pack the uncompressed data 8 times smaller. And then as @Luke has answered, specify a compression to use. There are a dozen different compression methods; another good one is COMPRESS=DEFLATE.

gdal_calc -A map.tif --outfile=out.tif --type=Byte --co="NBITS=1" --co="COMPRESS=DEFLATE" --calc="A >= 7"

With some example data that I have, I'm seeing a compression ratio of 0.15%. So I'd expect a result from a 1.37GB file to compress down to about 2MB.

Bonus question

According to the help for --calc:

calculation in gdalnumeric syntax using +-/* or any numpy array functions (i.e. logical_and())

The expression is processed by eval. So try this:

--calc="logical_or(logical_and(A >= 7, A <= 9), logical_and(A >= 10, A <= 12))"

I wasn't sure what the whole * 2 part of your original expression was, so it is left out.

  • Hmm, was trying to get output such that values 7 <= A <= 9 would evaluate to 1, and values 10 <= A <= 12 would evaluate to 2, using a raster mask as described here. However, although logical_and(A >= 10, A <= 12) * 2 evaluates to 2 for inputs 10, 11, 12, adding it as the second input to the logical_or function results in all inputs 7 <= A <= 12 returning 1 (I guess b/c when 'logical_or` evaluates 2, it reads it as True, which returns 1). Aug 24 '13 at 5:17
  • Update: apparently logicals here are not evaluated the same as logicals elsewhere. E.g. in python, False or 2 returns 2 while here it returns 1. I can get the result I need by running gdal_calc three times--one to produce the value 1 for 7,8,9; a second time to produce the value 2 for 10,11,12; and third time to combine them--but wondering if there's a better way. Aug 24 '13 at 5:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.