aerial photo mosaic

Malcolm Williamson malcolm at
Fri Aug 15 09:54:41 EDT 1997

On Fri, 15 Aug 1997, Simon Cox wrote:

> Joe - r.patch messes with the color table in an 
> attempt to maintain the appearance of the output.  
> It treats the raster's as category maps, rather than 
> continuous fields, so pixels with similar values do 
> *not* get assigned similar colors.  
> However, since the GRASS display colour-space is 
> restricted to 216 colours, this usually fails for 
> rasters with a large number of categories, such as images.  
> Images are a particular problem, of course, since adjacent 
> scenes frequently have different average levels, so features 
> which any intelligent observer would interpret as continuous 
> across the join will be really messed up.  Mosaicing 
> remote-sending images successfully is a long-standing 
> problem.  If you intend to do quantitative analysis you 
> more-or-less have to do it one frame at a time.  
> If you just want somthing that looks OK, than try manipulating 
> the color look-up-table, either manually by editing 
> gisdbase/location_name/mapset/cell/colr/map 
> or by using r.colors 
> (NB d.colors only changes the display so 
> does not persist between sessions).  

Let me expand on the above statement - d.colors _does_ permanently affect 
your colortable _if_ you use the "save color table" (the "c" key) option. 
I've been using it for years to edit my color table.
	-Malcolm Williamson

> -- 
> __________________________________________________
> Dr Simon Cox - Australian Geodynamics Cooperative Research Centre
> CSIRO Exploration & Mining, PO Box 437, Nedlands, WA 6009 Australia
> T:  +61 8 9389 8421   F:  +61 8 9389 1906   Simon.Cox at

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