> On Jul 30, 2015, at 9:29 PM, Nyall Dawson <[email protected]> wrote: > On 31 Jul 2015 11:07 am, "Nick Papadonis" <[email protected] > <mailto:[email protected]>> wrote: > > > > HI Folks, > > > > I’m trying to use the following expression to pick up the red colored > > routes on a map in which I used the info pointer tool to get the band > > values for the color. > > > > (“m@1" < 238 AND “m@1" > 213 AND “m@2" < 123 AND “m@2" > 98 AND “m@3" < 125 > > AND “m@3" < 99) * 1 > > Should that last check be "m@3" > 99? > >
I corrected above to: (“m@1" < 238 AND “m@1" > 213 AND “m@2" < 123 AND “m@2" > 98 AND “m@3" < 125 AND “m@3” > 99) * 1 with the same results which is black output tiff. I then tried individual expressions for each band as separate steps (sanity check): (“m@1" < 238 AND “m@1" > 213) * 1 (“m@2" < 123 AND “m@2" > 98) * 1 (“m@3" < 125 AND “m@3” > 99) * 1 These all produce a masked image, however masked incorrectly because I’m evaluating only a single band in the Raster Calculator. When I combine evaluation of bands as above or below to pick pixels in color range: ((“m@1" < 238 AND “m@1" > 210) AND (“m@2" < 123 AND “m@2" > 94) AND (“m@3" < 130 AND “m@3" > 98)) * 1 I get a black image with no matches. I expected at least one pixel identified using this expression because I evaluate a pixel at 224, 108, 115 and there are many other pixels in above range. Does anyone know if my expression needs correction or the Raster Calculator can only evaluate a single band in the expression? Thanks again, Nick > Nyall > > > > > Unfortunately, when this expression is used the resulting map is black with > > no other pixels for the detected color. > > > > If I break down this expression to a simple “greater than” line for single > > band, then things work. > > > > Does anyone know where this expression needs to be corrected? > > > > Thanks again, > > Nick > > _______________________________________________ > > Qgis-user mailing list > > [email protected] <mailto:[email protected]> > > http://lists.osgeo.org/mailman/listinfo/qgis-user > > <http://lists.osgeo.org/mailman/listinfo/qgis-user>
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