Stefan, I’m operating over a single layer and 3 bands on that layer.
Nick > On Jul 31, 2015, at 2:48 AM, Stefan Kiefer <[email protected]> wrote: > > Hi Nick, > you are absolutely right. My thought was, that you get A layer with distinct > values to identify the road. For a mask you are on the right way, and I > either don't understand the behaviour except that you operate over three > layers, which of course should work. > Have you tryed to generate a composit of the three layers and mask the single > values resulting for road structures? (it's more or less what I expected from > my first approach.) > > cheers > > Stefan > > > Nick Papadonis <[email protected]> hat am 31. Juli 2015 um 08:31 > > geschrieben: > > > > > > Hi Stefan, > > > > It’s my understanding black has a value of 0 in the resulting layer. > > > > I tried this and it results in similar image to step (a) and also includes > > other colors at lower intensities mixed in with the red. The red has the > > highest intensity in the greyscale. I’m looking to create a binary image > > with just the colors of red in the palette I choose and using this trace > > vectors over the paths. > > > > Thanks, > > Nick > > > > > On Jul 31, 2015, at 2:04 AM, Stefan Kiefer <[email protected]> wrote: > > > > > > Hi Nick, > > > I believe it is black bcause you always get a value of "1". Unfortunately > > > I can not verify this, because I have no QGis by this moment. Most > > > propably you wanted to calculate: > > > > > > (“m@1" < 238 AND “m@1" > 213 AND “m@2" < 123 AND “m@2" > 98 AND “m@3" < > > > 125 AND “m@3” > 99) * ((“m@1" < 238 AND “m@1" > 210) * "m@1") + ((“m@2" < > > > 123 AND “m@2" > 94) * “m@2") + ((“m@3" < 130 AND “m@3" > 98) *“m@3")) > > > > > > cheers > > > > > > Stefan > > > > > > > Nick Papadonis <[email protected]> hat am 31. Juli 2015 um 07:49 > > > > geschrieben: > > > > > > > > > > > > One more comment. The resulting layer histogram is showing the pixel > > > > range spread over frequency in floating point values. Is the raster > > > > calculator performing floating point math with potential rounding error? > > > > > > > > I found it also interesting that the following expression resulted in a > > > > layer, which when inspected for band values, has integer values of 2 > > > > and 3. 3 being the value I want for the red route. > > > > > > > > a) ((“m@1" < 238 AND “m@1" > 210) * 1) + ((“m@2" < 123 AND “m@2" > 94) > > > > * 1) + ((“m@3" < 130 AND “m@3" > 98) * 1) > > > > > > > > I then change the expression to only use values 2 and greater and this > > > > shows properly: > > > > b) ((“m@1" < 238 AND “m@1" > 210) * 1) + ((“m@2" < 123 AND “m@2" > 94) > > > > * 1) + ((“m@3" < 130 AND “m@3" > 98) * 1) > 2 > > > > > > > > I then changed the expression to ensure all three values are obtained > > > > and it results in a black image of 0’s. I was expecting only the red > > > > route to appear as it resulted in value of 3 in step (a). > > > > > > > > ((“m@1" < 238 AND “m@1" > 210) * 1) + ((“m@2" < 123 AND “m@2" > 94) * > > > > 1) + ((“m@3" < 130 AND “m@3" > 98) * 1) > 2.1 > > > > ((“m@1" < 238 AND “m@1" > 210) * 1) + ((“m@2" < 123 AND “m@2" > 94) * > > > > 1) + ((“m@3" < 130 AND “m@3" > 98) * 1) >= 3 > > > > > > > > I’m wondering how much testing the Raster Calculator has gone through > > > > and if there is a possible bug here. Perhaps something to do with > > > > floating point? > > > > > > > > Thanks again > > > > > > > > > On Jul 31, 2015, at 12:39 AM, Nick Papadonis <[email protected]> > > > > > wrote: > > > > > > > > > > Folks, > > > > > > > > > > I’m using QGIS 10.1. The following expressions result in a black > > > > > raster of 0’s, when I expected only red pixels to appears in the > > > > > binary image indicating routes on a map: > > > > > > > > > > a) (“m@1" < 238 AND “m@1" > 213 AND “m@2" < 123 AND “m@2" > 98 AND > > > > > “m@3" < 125 AND “m@3” > 99) * 1 > > > > > b) ((“m@1" < 238 AND “m@1" > 210) * 1) * ((“m@2" < 123 AND “m@2" > > > > > > 94) * 1) * ((“m@3" < 130 AND “m@3" > 98) * 1) > > > > > > > > > > I then tried the following individual expressions for each band as > > > > > separate steps (sanity check) and they work to cover the pixels in > > > > > range: > > > > > c) (“m@1" < 238 AND “m@1" > 213) * 1 > > > > > d) (“m@2" < 123 AND “m@2" > 98) * 1 > > > > > e) (“m@3" < 125 AND “m@3” > 99) * 1 > > > > > > > > > > I then tried the following expression which appears to create a > > > > > proper greyscale image focusing on the red pixels. I replaced the > > > > > multiplication with addition to see what was happening: > > > > > f) ((“m@1" < 238 AND “m@1" > 210) * 1) + ((“m@2" < 123 AND “m@2" > > > > > > 94) * 1) + ((“m@3" < 130 AND “m@3" > 98) * 1) > > > > > > > > > > The resulting raster has a Min = 0 and Max = 1.998. I was expecting > > > > > it to be Min = 0 and Max = 3. The value of 3 would indicate all 3 > > > > > bands were positive on color match. I then go to the layer properties > > > > > and load calculate min/max again and it is Min = 0 and Max = 3. I > > > > > tried to change the min/max settings on they layer and these settings > > > > > will not stay set. The layer goes back to Max = 1.998. What’s even > > > > > more odd is the max being a floating point number. I suspect that may > > > > > be part of the issue. Anyone know why this is the case for integer > > > > > band values? Has anyone successfully used the Raster Calculator to > > > > > perform this sort of work before? > > > > > > > > > > Thanks again, > > > > > Nick > > > > > > > > _______________________________________________ > > > > Qgis-user mailing list > > > > [email protected] > > > > http://lists.osgeo.org/mailman/listinfo/qgis-user > > > _______________________________________________ > Qgis-user mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/qgis-user _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
