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Color Palette Tables (.cpt) for Matlab

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Color Palette Tables (.cpt) for Matlab

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04 Oct 2010 (Updated )

Create and apply GMT-style colormaps in Matlab

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Description

This function creates and applies a colormap defined in a color palette table (.cpt) file. Color palette tables are used to define colormaps in the Generic Mapping Tools package (http://gmt.soest.hawaii.edu/). These files provide more flexible colormapping than Matlab's default schemes, including both discrete and continuous gradients, as well as easier direct color mapping.
For a complete description of the color palette table format, see the GMT documentation.
This package includes 20 standard GMT colormaps; please see the header of each file for copyright information. Many more color tables are available on the cpt-city website (http://soliton.vm.bytemark.co.uk/pub/cpt-city/index.html).

Acknowledgements

This file inspired Cmap2pal Convert Matlab Colormap To Binary .Pal Format.

MATLAB release MATLAB 7.10 (R2010a)
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Comments and Ratings (17)
07 Oct 2013 Kelly Kearney

I've addressed Seth's question via email. But in case others encounter this, the behavior he was seeing is as intended. While the length of the resulting colormap can be specified via the ncol input, the number of unique colors in that colormap is determined by the .cpt file itself. The GMT_Haxby colormap defines 32 specific colors, so increasing the resolution of the colormap via ncol will create a larger colormap array, but many of these values will simply be replicates.

05 Oct 2013 Seth

More detail on my comment below:

cptcmap('GMT_Haxby','ncol', 4) produces a contour plot with four colors;
cptcmap('GMT_Haxby','ncol', 8) produces a contour plot with eight colors;
cptcmap('GMT_Haxby','ncol', 32) produces a contour plot with thirty-two colors;

However, cptcmap('GMT_Haxby','ncol', 256) produces a contour plot with 32 colors, not 256 colors. Any number above 32 leads to a plot with just 32 colors.

Matlab novice, hope I'm not missing something trivial!

04 Oct 2013 Seth

I'm having trouble getting these contour plots to use more than ~32 colors with this function.

If I use the command:

colormap(jet(256));

then contour plots plot using the jet colorscheme with 256 colors. However, if I use the command:

cptcmap('GMT_Haxby','ncol', 256);

then all of the subsequent contour plots display with only ~32 colors.

Any suggestions? Thanks!

16 Apr 2013 Claire

Function works brilliantly!! Thanks so much!

28 Mar 2013 Kelly Kearney

@Claire

Sorry, I always forget that roundn is part of the Mapping toolbox. Just replace the roundn call:

space = roundn(space, -3);

with

space = round(space*1e3)/1e3;

27 Mar 2013 Claire

I don't have access to the "roundn" function. Is there a work around so that I can get your function working?

03 Jan 2013 Frank Engel

Excellent and very useful. Works as expected, and had no problems using with gradients provided from cpt-city (http://soliton.vm.bytemark.co.uk/pub/cpt-city/)

01 Oct 2012 Jesse Hansen

Very useful for bathymetric mapping. Please note that there is a dependency on the mapping toolbox due to the use of the 'roundn' function. This could easily be replaced by 1 line of standard Matlab code.

16 Jul 2012 angela  
28 Mar 2012 Kelly Kearney

@camilo melo,

I don't have R20011b, so I can't test it, but I can't think of any reason it wouldn't work in that version. Based on the error message you mention, my guess is you tried to call the function without any input arguments; it needs at least one (the name of the colormap).

27 Mar 2012 camilo melo

hi, does this function works for MATLAB R2011b?? i tried to use it but got this error message Index exceeds matrix dimensions.

Error in cptcmap (line 123)
[blah, blah, ext] = fileparts(varargin{1});

03 Apr 2011 Felipe G. Nievinski

Another one, trying

cptcmap('sst')

Just had to replace

if ~strcmp(varargin{1}(end-3:end), '.cpt') % without extension

for:

if (numel(varargin{1}) <= 4) || ~strcmp(varargin{1}(end-3:end), '.cpt') % without extension

03 Apr 2011 Felipe G. Nievinski

Another one, trying

cptcmap('sst')

Just had to replace

if ~strcmp(varargin{1}(end-3:end), '.cpt') % without extension

for:

if (numel(varargin{1}) <= 4) || ~strcmp(varargin{1}(minend-3:end), '.cpt') % without extension

03 Apr 2011 Felipe G. Nievinski

You might want to replace l.83:

cptpath = './cptfiles';

with:

cptpath = fullfile(fileparts(which('cptcmap')), 'cptfiles');

That way the source code needs not be modified when first downloading the package or later when moving the routine files around.

I was having problems trying

cptcmap('elevation')

where elevation.cpt was downloaded from cpt-city and placed in the cptpath; it turns out that l.98,

if exist(varargin{1}, 'file') % full filename and path given

would find this other file instead:

which elevation
C:\Program Files\MATLAB\R2009b\toolbox\map\map\elevation.m

You might want to replace the block l.98-111 with the following (minimally modified):

if ~strcmp(varargin{1}(end-3:end), '.cpt') % without extension
varargin{1} = [varargin{1} '.cpt'];
end
if exist(varargin{1}, 'file') % full filename and path given
filename = varargin{1};
else % only file name given
filename = fullfile(cptpath, varargin{1});
if ~exist(filename, 'file')
error('Specified .cpt file not found');
end
end

Finally, not sure why the __MACOSX subdirectory is being distributed.

26 Mar 2011 Felipe G. Nievinski

Great idea, always wanted to make my matlab maps look like gmt's. Also thanks for pointing out to cpt-city, it's a great collection.

You might want to use the acknowledgement field in the FEX form, so that your submission is back-linked from related entries, e.g., 28982 and the ones linked from there.

11 Oct 2010 Kelly Kearney

Marios,

If by the inverse colormap, you mean you want to flip the direction of the colors, then yes, use the 'flip' option:

cptcmap('GMT_seis', 'flip', true)

-Kelly

11 Oct 2010 Marios Karaoulis

Hi. Very nice package. Is it possible to use the inverse colormap of GMT_seis.cpt?

Updates
12 Apr 2011

-bug fixes where some input filenames were misinterpreted (thanks to Felipe)
-colormap display option no longer relies on external functions, has cleaner display, and renders more quickly

24 Apr 2013

Replaced roundn call with manual calculation to remove unintended dependency on Mapping Toolbox.

08 Jul 2013

Added error check in case no input is supplied. Also corrected the roundn issue (correctly, this time).

10 Jul 2014

- Corrected bug in HSV color calculation
- Updated for 2014b graphics

28 Aug 2014

Corrected bug in colormap length calculation

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