Search code examples
matlabcolorsgeospatialraster

MATLAB: Plot raster map with custom colormap

In MATLAB, I have a matrix map_data associated with referencing object R (both in this MAT-file). I want to map it with a discrete colorbar given an irregular range of values to look something like this:

enter image description here

I would like to use geoshow() or something similar that allows me to reproject at will and to overlay shapefiles on top of the raster. But really anything that gets me on the right track would be much appreciated.

I'm using MATLAB r2014b. Here is the relevant information for the colormap:

                                R    G    B
0     <= map_data < 0.001     204  204  204
0.001 <= map_data < 0.005     153  153  153
0.005 <= map_data < 0.01      255  255  178
0.01  <= map_data < 0.05      254  204   92
0.05  <= map_data < 0.1       253  141   60
0.1   <= map_data < 0.25      240   59   32
0.25  <= map_data < 0.5       189    0   38
0.5   <= map_data < 1           0    0    0

Cross-posted at MATLAB answers.

Solution

  • Will had a great idea to use histc(), but I had to edit his code to make it work for me. Here's what I ended up with.

    my_colormap = [204  204  204
               153  153  153
               255  255  178
               254  204   92
               253  141   60
               240   59   32
               189    0   38
                 0    0    0]/255 ;
binEdges = [0 0.001 0.005 0.01 0.05 0.1 0.25 0.5 1] ;
labels = textscan(num2str(binEdges*100),'%s') ;
labels = labels{1} ;
labels{length(labels)} = [labels{length(labels)} '%'] ;

[~,indices] = histc(map_data,binEdges);
indices(isnan(map_data)) = NaN ;
indices(isinf(map_data)) = NaN ;

figure ;
pcolor(indices-1)   % Instead of image(), to display NaN values as white
shading flat
axis equal tight

colormap(gca,my_colormap);   % gca as first argument prevents 
                             % colormap from changing for all 
                             % subsequent plots
h = colorbar;
caxis([0 length(binEdges)-1])
h.YTickLabel = labels ;

    Resulting plot