Hello there,
I just realize I've used r.composite for ages without wondering how I
could perform the reverse task. The thing is I ran r.composite on a 3
band geotiff orthoimage, dropped the initial .red, .green and .blue
rasters, and I would need them now in order to run r.out.vtk with the
rgbmaps argument. Dummy...
A quick glance at the composite raster color table makes me think it
might be quite easy to do. Is there a command for this opération or
should I try to write a script to do the job ?
Thank you,
Vincent
On Mon, Nov 25, 2013 at 7:22 AM, Vincent Bain <bain@toraval.fr> wrote:
Hello there,
I just realize I've used r.composite for ages without wondering how I
could perform the reverse task. The thing is I ran r.composite on a 3
band geotiff orthoimage, dropped the initial .red, .green and .blue
rasters, and I would need them now in order to run r.out.vtk with the
rgbmaps argument. Dummy...
You can use the # operator of r.mapcalc:
r.mapcalc "map.red = r#map"
r.mapcalc "map.green = g#map"
r.mapcalc "map.blue = b#map"
Markus M
A quick glance at the composite raster color table makes me think it
might be quite easy to do. Is there a command for this opération or
should I try to write a script to do the job ?
Thank you,
Vincent
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Thank you much Markus,
never noticed this mapcalc operator before, great !
Vincent
Le lundi 25 novembre 2013 à 12:10 +0100, Markus Metz a écrit :
On Mon, Nov 25, 2013 at 7:22 AM, Vincent Bain <bain@toraval.fr> wrote:
> Hello there,
>
> I just realize I've used r.composite for ages without wondering how I
> could perform the reverse task. The thing is I ran r.composite on a 3
> band geotiff orthoimage, dropped the initial .red, .green and .blue
> rasters, and I would need them now in order to run r.out.vtk with the
> rgbmaps argument. Dummy...
You can use the # operator of r.mapcalc:
r.mapcalc "map.red = r#map"
r.mapcalc "map.green = g#map"
r.mapcalc "map.blue = b#map"
Markus M
>
> A quick glance at the composite raster color table makes me think it
> might be quite easy to do. Is there a command for this opération or
> should I try to write a script to do the job ?
>
> Thank you,
> Vincent
>
> _______________________________________________
> grass-user mailing list
> grass-user@lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user
Markus Metz wrote:
> I just realize I've used r.composite for ages without wondering how I
> could perform the reverse task. The thing is I ran r.composite on a 3
> band geotiff orthoimage, dropped the initial .red, .green and .blue
> rasters, and I would need them now in order to run r.out.vtk with the
> rgbmaps argument. Dummy...
You can use the # operator of r.mapcalc:
r.mapcalc "map.red = r#map"
r.mapcalc "map.green = g#map"
r.mapcalc "map.blue = b#map"
Note that GRASS 7 has the r.rgb script which does just this.
Also, note that an r.composite+r.rgb round-trip normally loses
accuracy. By default, the maps generated by r.composite only use 32
levels for each component (equivalent to a 15-bpp image).
You can avoid this with "r.composite ... levels=256", but the
resulting maps will have much larger colour tables (65536 rules rather
than 1024), which can make certain operations significantly slower.
--
Glynn Clements <glynn@gclements.plus.com>
OK for the caution Glynn,
for my particular concern I finally re-ran the process from the source
files.
Thank you,
V.
Le mardi 26 novembre 2013 à 19:07 +0000, Glynn Clements a écrit :
Markus Metz wrote:
> > I just realize I've used r.composite for ages without wondering how I
> > could perform the reverse task. The thing is I ran r.composite on a 3
> > band geotiff orthoimage, dropped the initial .red, .green and .blue
> > rasters, and I would need them now in order to run r.out.vtk with the
> > rgbmaps argument. Dummy...
>
> You can use the # operator of r.mapcalc:
>
> r.mapcalc "map.red = r#map"
> r.mapcalc "map.green = g#map"
> r.mapcalc "map.blue = b#map"
Note that GRASS 7 has the r.rgb script which does just this.
Also, note that an r.composite+r.rgb round-trip normally loses
accuracy. By default, the maps generated by r.composite only use 32
levels for each component (equivalent to a 15-bpp image).
You can avoid this with "r.composite ... levels=256", but the
resulting maps will have much larger colour tables (65536 rules rather
than 1024), which can make certain operations significantly slower.