[GRASS-user] Need for a custom color map

[Thomas.Adams at noaa.gov]

Glynn,

Thanks for your help. Sorry that I was vague about what I was after. It looks like the first one is what I want, because I do want white to represent 0 difference.

Regards,
Tom

----- Original Message -----
From: Glynn Clements <glynn at gclements.plus.com>
Date: Friday, October 19, 2007 4:32 pm
Subject: Re: [GRASS-user] Need for a custom color map

> 
> Thomas Adams wrote:
> 
> > I'm wondering if someone has a color map that has white in the 
> middle 
> > range and blue at one extreme and red at the other. I'm creating 
> a 
> > precipitation difference map for data quality control purposes 
> and I'm 
> > trying to identify areas of over- and under-estimation by radar 
> > estimates relative to gauge-only estimates. Such a scale would be 
> > helpful to those looking for differences.
> 
> The "differences" map (i.e. "r.colors ... color=differences") is:
> 
> 	0% blue
> 	0 white
> 	100% red
> 
> This may be suitable, depending upon what you mean by "white in the
> middle". The above has white at zero, which isn't necessarily the
> middle. If you want white at the midpoint between the minimum and
> maximum values, use:
> 
> 	0% blue
> 	50% white
> 	100% red
> 
> If you want the table to be symmetrical, you'll need to specify
> absolute values rather than percentages, e.g.:
> 
> 	-10 blue
> 	0 white
> 	10 red
> 
> -- 
> Glynn Clements <glynn at gclements.plus.com>
>