[GRASS-user] Errors applying color rules and -g flags in r.colors

[Patton, Eric]

Thanks, that clears up all the outstanding issues.

A while back I think I recall someone saying that they had implemented a
C structure that would allow a color-picker to be used in Grass
programs. Would it be much difficulty adding this color-picker dialog to
r.colors to assist in constructing custom color rules files? It seems to
me that this module would be the ideal place to have such a feature. 

--
Eric Patton 
email: epatton at nrcan.gc.ca

 

> -----Original Message-----
> From: Glynn Clements [mailto:glynn at gclements.plus.com] 
> Sent: Thursday, April 19, 2007 4:40 PM
> To: Patton, Eric
> Cc: grassuser at grass.itc.it; grass-dev at grass.itc.it
> Subject: RE: [GRASS-user] Errors applying color rules and -g 
> flags in r.colors
> 
> 
> Patton, Eric wrote:
> 
> > I've updated my cvs to include your latest fix to 
> color_rules.c, and 
> > while I'm not receiving the error message I did before, 
> there is still 
> > some puzzling behavior occurring.
> > 
> > The color tables aspectcolr, evi, ndvi, population, and slope still 
> > display an all-white raster when invoked with no flags. However, 
> > applying the -e flag to each of these color tables creates a 
> > full-color, histogram-equalized color table as requested. I'm using 
> > the same floating-point raster as I did previously. Is this 
> expected 
> > given the types of color tables being used? I'm not 
> familiar with what 
> > 'evi' or 'ndvi' mean and for what types of data they are 
> best suited.
> 
> The aspectcolor, population and slope tables only cover 
> positive values, while the evi and ndvi tables cover the 
> range -1 to 1, so it's expected that those tables won't work 
> with the data in question.
> 
> OTOH, -e maps the range of the data to the range of the 
> tables; the absolute values used in the tables don't matter.
> 
> In general, tables which associate colors with percentages 
> (aspect, bcyr, byg, byr, elevation, grey, gyr, rainbow, ramp, 
> ryb, ryg and
> wave) can be applied to any data, while those which use 
> absolute values (aspectcolr, curvature, etopo2, evi, ndvi, 
> population, slope, srtm, and terrain) only make sense for 
> data with certain ranges.
> 
> You can get a rough idea of the applicability of a colour 
> table by reading the corresponding rules file 
> ($GISBASE/etc/colors/<name>). 
> E.g. slope is defined as:
> 
> 	0   255 255 255
> 	2   255 255   0
> 	5     0 255   0
> 	10    0 255 255
> 	15    0   0 255
> 	30  255   0 255
> 	50  255   0   0
> 	90    0   0   0
> 
> This is designed for the slope map generated by 
> r.slope.aspect, where the value is a slope angle between 0 
> and 90 degrees.
> 
> Similarly, the aspectcolr map:
> 
> 	0 white
> 	1 yellow
> 	90 green
> 	180 cyan
> 	270 red
> 	360 yellow
> 
> is designed for the aspect maps produced by r.slope.aspect, 
> where the value is a heading between 0 and 360 degrees.
> 
> [The "aspect" map should probably also use 0-360 rather than 
> 0%-100%; I'm not sure why it doesn't.]
> 
> --
> Glynn Clements <glynn at gclements.plus.com>
>