I would prefer to obtain in one step the absolute value of the difference between two pixels, in part because I do not see the meaning of a negative pixel value. In my example, I do not see meaning to a signed byte value for a pixel channel being red=-51. Greg
On Feb 1, 2010, at 3:08 AM, Antonio Valentino wrote: > Hi Greg, > > Il giorno Sun, 31 Jan 2010 14:58:19 -0500 > Greg Coats <gregco...@mac.com> ha scritto: > >> Regarding the diff function >> "diff": computes the difference between 2 raster bands (b1 - b2) >> Since the result of diff could be a negative number, for example >> 99-150=-51, I suggest that there be an additional function that >> provides the absolute value of diff, which would be 51 in this >> example. Greg > > Of course, it would not be a problem to include but my original idea > was to provide only base functions and use them to get complex > expressions. > > In this case, what you need can be obtained using two stacked virtual > files: > - diff (using appropriate band data type and SourceTransferType) > - mod > > Is it a reasonable approach for you? > > Even more interesting for common tasks should be to compute > > abs((b1-b2)/(b1+b2)) > > >> On Jan 31, 2010, at 12:18 PM, Antonio Valentino wrote: >> >>> Hi Matt, >>> >>> Il giorno Mon, 25 Jan 2010 20:57:58 -0600 >>> Matt Klaric <m...@klaric.com> ha scritto: >>> >>>> On Mon, Jan 25, 2010 at 8:38 PM, Frank Warmerdam >>>> <warmer...@pobox.com>wrote: >>>> >>>>> I don't think the VRT approach supports actually adding >>>>> different images together, only overlaying and rescaling. >>>>> >>>>> >>>> However, pixel functions could be used in a VRT file to accomplish >>>> the desired outcome. >>>> >>>> --matt >>> >>> Indeed, it would require a pixel function for sum and the ScaleRatio >>> property of ComplexSource. >>> >>> I have just submitted a patch >>> >>> http://trac.osgeo.org/gdal/ticket/3367 >>> >>> that provides a set of standard pixel functions, including sum (of 2 >>> or more raster bands). >>> >>> Using this set of functions it should be quite easy to write a >>> python program that performs generic bands arithmetic. > > > best regards > > -- > Antonio Valentino _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
