Hi Havard, Unfortunately, the expression below results in a complete black TIFF. I am referencing the correct layer. Any ideas?
Thanks Nick > On Jul 29, 2015, at 4:34 PM, Håvard Tveite <[email protected]> wrote: > > With QGIS 2.10, the following should work (probably also OK > for earlier versions). > > Check the band values of your colour using the info button, > and use the values in the expression below (assuming the > name of your raster layer is yourraster) instead of 116, 20 > and 31: > > ("yourraster@1" = 116 AND "yourraster@2" = 20 AND "yourraster@3" = 31) * 1 > > This should give you a binary raster with 1 in the pixels > that have your colour and 0 in the pixels with other colours. > > In the style dialogue you can use the following to see the > resulting binary image: > Colour gradient: "white to black" > Min: 0 > Max: 1 > > You should be able to use r.thin on that image, but I am not > able to test this now, as I am on Ubuntu, and have not been > able to get GRASS to work through Processing on that platform > for QGIS 2.10. > > Håvard > > On 29. juli 2015 16:40, Nick Papadonis wrote: >> Hi Håvard, >> >> I found the raster calculator and read the online manual for it, however am >> still a bit lost. I was also playing with the Style properties and color >> bands last night to try to accomplish this. I was unable to get a single >> binary image with the single color (red in this case). I think the >> understand the r.thin suggestion and that it will thin the single color >> thick lines for vectorization. Appreciate if you can expand on obtaining a >> binary skeleton of the one color of the trails. >> >> Thanks again, >> Nick >> >>> On Jul 29, 2015, at 7:18 AM, Havard Tveite <[email protected]> wrote: >>> >>> If you are going to use GRASS r.to.vect (for instance through QGIS >>> Processing), you will need a binary skeleton image. >>> You could get one by using the raster calculator to extract >>> your single colour as a binary image, and then GRASS r.thin >>> (available in QGIS Processing) to get the skeleton. >>> >>> Håvard >>> >>> On 29/7/2015 8:36:AM, Nick Papadonis wrote: >>>> Hi Folks, >>>> >>>> I have a map with numerous trails in a single color and would like to >>>> vectorize these. Is there a mode Qgis can be placed in such that a color >>>> can be selected for inclusion in the vectorization process? I.e. to make >>>> converting these routes to vector format easier? >>>> >>>> Thanks again >>>> _______________________________________________ >>>> 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
