[GRASSLIST:700] Re: patching together aerial photographs

[Glynn Clements]

Jeroen Wortel wrote:

> I have a series of georeferenced aerial photographs as 8 bit tiff files.
> I have imported these into Grass using r.in.gdal and can visualize 
> them with d.rast
> Now I want to patch them together in order to use them in NVIZ as color raster.
> 
> Because the images are 8 bit indexed colours I can't use r.patch to 
> patch the images together in one go.
> I suppose I have to split the images first into red, green and blue 
> bands, patch each band together with r.patch, and combine the patched 
> red, green and blue bands again.
> 
> I can't find the Grass command to split the raster image in to red, 
> green and blue rasters. How do I do this in Grass?

	r.mapcalc 'map.r = r#map ; map.g = g#map ; map.b = b#map'

> Is there another way of achieving a patched image of the aerial
> photographs?

You could convert the separate R/G/B maps to a single composite colour
map before patching, although this will degrade the colour resolution
(24-bpp composite images aren't practical).

You could convert the images to either RGB or to a common palette
using image-processing software prior to importing. If you import an
RGB image with r.in.gdal, it will import it as separate R/G/B
channels.

The ideal solution would be to get hold of the original RGB images.

-- 
Glynn Clements <glynn at gclements.plus.com>