[GRASS-user] Need for a custom color map

[Glynn Clements]

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>