On Thursday 03 of October 2013 15:47:59 Gregory Penn wrote: > I think that r.blend may accomplish what I need, in terms of compositing > rasters to achieve the effect of partial transparency in a layer. It is not > clear to me how this will work when one or more of the layers that I want > to composite has rgb channels and so is represented by three separate > raster maps (one for each channel) in the mapset.
You can utilise r.composite, in first place, to compose Real- or Pseudo-RGBs. <http://grass.osgeo.org/grass64/manuals/r.composite.html>. Try to find an optimum for your RGBs (friends: r.colors, i.landsat.rgb). > Do I need to create an > image group (i.group) of the three channels and use the group's name as > 'first' or 'second' parameter for r.blend? See above. Note, anyhow, that you can export directly a group that consists of three maps, say Red, Green and Blue bands of a satellite acquisition as an example, by using the group's name directly with r.out.gdal. Maybe a useful tip (?). > The documentation for r.blend seems to indicate that it can only blend two > rasters at a time. True. So, r.composite first. "r.blend" itself will produce R, G and B which you need to display with d.rgb, then, I think, use d.out.png. Or, once again, after "blending", r.composite the final R, G and B maps, then export (r.out.gdal or d.out.*). I think it'll work this way. Don't remember currently another way. Best, Nikos --%<---%<--- On Thursday 03 of October 2013 11:44:38 Gregory Penn wrote: > >> I am attempting to create maps from the command line, which are > >> composites > >> of several raster and vector layers. Nikos: > > Working on GRASS 6.x or 7? > >> In order to visualize the data effectively, I need to vary the opacity of > >> the layers. I have found that this is simple to achieve in the wxGUI, but > >> the GUI does not display the underlying module call as it does with many > >> other commands. A little Googling helped me to discover a module called > >> g.pnmcomp, which was apparently used by the old Tcl/Tk GUI for managing > >> layer opacity, but that module appears not to be intended for end users > >> and I suspect that there is an easier and more direct way to achieve my > >> desired results. > > Check r.blend: <http://grass.osgeo.org/grass64/manuals/r.blend.html>, > > <http://grass.osgeo.org/grass70/manuals/r.blend.html>. The latter > > features a "-c" flag, which does... "Combine resulting R,G,B layers into > > single output map". > >> The process by which I'm creating my maps is essentially this sequence of > >> commands (is there a better approach?): > >> g.region rast=region_raster.tif > >> d.mon start=PNG > >> d.rast map=some_raster.tif > >> d.rast map=another_raster.tif > >> d.vect map=some_vector.shp > >> d.mon stop=PNG > > Ah, this is GRASS6.x then. I think you can still blend maps and then maybe > > use d.out.png to export? See > > <http://grass.osgeo.org/grass64/manuals/d.out.png.html>. > >> It seems to me that either d.mon or the PNG driver is doing the > >> compositing and so would handle the opacity of the layers, but I can't > >> find any documentation of how to specify values for opacity. This is > >> surprising to me because it seems that what I'm trying to do is such a > >> basic and commonly used operation in creating maps. What am I missing? > > Hope this is what you are looking for. > > Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
