[GRASS-user] Need for a custom color map

GRASS GRASS user
1

List:

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.

Thanks,
Tom

--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL: thomas.adams@noaa.gov

VOICE: 937-383-0528
FAX: 937-383-0033

2

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@gclements.plus.com>

3

Tom,

did you try the "differences" color map from r.colors [1]?
It is defined as

0% blue
0 white
100% red

It was added by Helena for such scopes.

Markus

[1] lib/gis/colors/differences

Thomas Adams wrote:

List:

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.

Thanks,
Tom

--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL: thomas.adams@noaa.gov

VOICE: 937-383-0528
FAX: 937-383-0033

--
View this message in context: http://www.nabble.com/Need-for-a-custom-color-map-tf4655431.html#a13302628
Sent from the Grass - Users mailing list archive at Nabble.com.

4

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@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@gclements.plus.com>

5

J.,

Thanks for your help; that's a very nice reference to have with the different color palettes…

Regards,
Tom

----- Original Message -----
From: "J.J.Green" <j.j.green@sheffield.ac.uk>
Date: Friday, October 19, 2007 4:19 pm
Subject: Re: [GRASS-user] Need for a custom color map

Tom

> 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.
GMT polar at

  http://sview01.wiredworkplace.net/pub/cpt-
city/gmt/tn/GMT_polar.png.index.html
sounds about right, convert with

  http://bambi.otago.ac.nz/hamish/grass/r.cpt2grass

-j
--
J.J. Green, Dept. Applied Mathematics, Hicks Bld.,
University of Sheffield, UK. +44 (0114) 222 3742
http://sview01.wiredworkplace.net/pub/jjg

6

Thomas,

Just make your own. Pick the color rules option from the raster menu. Select
the map you want, then enter rules in the text box. To make this kind of
color table, enter the following:

0% blue
0 white
100% red

Michael

On 10/19/07 12:46 PM, "Thomas Adams" <Thomas.Adams@noaa.gov> wrote:

List:

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.

Thanks,
Tom

__________________________________________
Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

7

Markus (and others),

Thanks for your response(s); the 'differences' color map from r.colors is exactly what I was looking for. This will be extremely helpful!

Regards,
Tom

Markus Neteler wrote:

Tom,

did you try the "differences" color map from r.colors [1]?
It is defined as

0% blue
0 white
100% red

It was added by Helena for such scopes.

Markus

[1] lib/gis/colors/differences

Thomas Adams wrote:
  

List:

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.

Thanks,
Tom

--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL: thomas.adams@noaa.gov

VOICE: 937-383-0528
FAX: 937-383-0033

--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL: thomas.adams@noaa.gov

VOICE: 937-383-0528
FAX: 937-383-0033