I have a raster map (-100 to +100) and I need to get all the minus values as absolute values (-100=100; -99=99...). How can I do this? Is it something like reclassify?
You could use the Raster Calculator to do this. Square the pixel values to ensure all values are positive, and then extract the square roots to get back original number. Something like this:
sqrt ( myraster@1 * myraster@1 )