Different colors for different ranges of data

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JDilla 2016-10-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/308748-different-colors-for-different-ranges-of-data

评论： Walter Roberson 2017-7-20

figure
latlim = [-15 15];
longlim = [90 125];
worldmap(latlim, longlim)
load coast
geoshow(lat, long)
samplefactor = 1;
[Z, refvec] = etopo('etopo1_bed_c_i2.bin',samplefactor,latlim,longlim);
geoshow(Z, refvec, 'DisplayType', 'texturemap');
demcmap(Z, 256);
geoshow('landareas.shp', 'FaceColor', 'none', ...
   'EdgeColor', 'black');
load Sumatra_catalog.txt
    plotm(Sumatra_catalog(:,1),Sumatra_catalog(:,2),'k.') 
    %depth = (Sumatra_catalog(:,3))

What this code does is loads a text file containing earthquake latitude, longitude and depth data. It plots the data onto a coastline as block dots.. What I want to do, is change the colour of the dots based on the different depths. For example, black for depths of 0-100, red for depths of 101-200, blue for 201-300 and so forth.

I was thinking of using a for loop with else/if statements, I've had a look at the documentation but I'm not sure how how to implement.

Any help appreciated.

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采纳的回答

Walter Roberson 2016-10-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/308748-different-colors-for-different-ranges-of-data#answer_240326

在 MATLAB Online 中打开

Change

    plotm(Sumatra_catalog(:,1),Sumatra_catalog(:,2),'k.') 
    %depth = (Sumatra_catalog(:,3))

pointsize = 20;    %adjust as needed
depth = (Sumatra_catalog(:,3));
cmap = [0 0 0; %0 - 100
        1 0 0; %101-200
        0 0 1;]; %201-300
depthind = min( max(0, floor((depth-1) / 100) ), size(cmap,1)-1) + 1;   %first bin is wider than the rest
scatterm(Sumatra_catalog(:,1), Sumatra_catalog(:,2), pointsize, cmap(depthind,:));

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Walter Roberson 2016-10-24

在 MATLAB Online 中打开

Yes, there is an alternative code:

cmap = [0 0 0; %0 - 100
      1 0 0; %101-200
      0 0 1;]; %201-300
pointsize = 20;
scatterm( Sumatra_catalog(:,1), Sumatra_catalog(:,2), pointsize, Sumatra_catalog(:,3) );
caxis([0 300]);   %the upper limit should match the upper limit appropriate for the color table
colormap(cmap);

This approach will work provided that the range divides exactly equally into the number of colors in the colormap. For example if you wanted a level which was 301-350 (half the size of the others) then it would not work. The approach of creating the index, that I posted above, would be needed in such a case.

An alternate approach to creating an index would be to use histc():

cmap = [0 0 0; %0 - 100
      1 0 0; %101-200
      0 0 1;]; %201-300
[~, depth_bin] = histc( Sumatra_catalog(:,3), [0, 101, 201, 301]);
color_triples = cmap(depth_bin, :);  %transform the index into an RGB triple
pointsize = 20;   %adjust as needed
scatterm( Sumatra_catalog(:,1), Sumatra_catalog(:,2), pointsize, color_triples );

This has the advantage of making it easy to tweak the boundaries

JDilla 2016-10-24

在 MATLAB Online 中打开

clear
figure
latlim = [-15 15];
longlim = [90 125];
worldmap(latlim, longlim)
load coast
geoshow(lat, long)
samplefactor = 1;
[Z, refvec] = etopo('etopo1_bed_c_i2.bin',samplefactor,latlim,longlim);
geoshow(Z, refvec, 'DisplayType', 'texturemap');
demcmap(Z, 256);
geoshow('landareas.shp', 'FaceColor', 'none', ...
   'EdgeColor', 'black');
load Sumatra_catalog.txt
      [~, depth_bin] = histc( Sumatra_catalog(:,3), [0, 50, 100, 200, 300, inf]);
  cmap = [0 0 0;  %0 <= depth < 50    %this is black
          1 0 0;  %50 <= depth < 100  %this is red
          1 1 0;  %100 <= depth < 200 %this is yellow
          0 0 1;  %200 <= depth < 300 %this is blue
          0 1 0;];%300 <= depth       %this is green
  pointsize = 20;
  scatterm(Sumatra_catalog(:,1), Sumatra_catalog(:,2), pointsize, cmap(depth_bin,:));

Error using scatter (line 81) CData must be an RGB triplet, an M-by-1 vector of the same length as X, or an M-by-3 matrix.

Error in internal.mapgraph.GeoScatterGroup (line 70) scatter(x, y, sizedata, cdata, ...

Error in scatterm (line 62) mapgraph = internal.mapgraph.GeoScatterGroup(ax, lat, lon, args{:});

Error in practical4 (line 32) scatterm(Sumatra_catalog(:,1), Sumatra_catalog(:,2), pointsize, cmap(depth_bin,:));

JDilla 2016-10-26

this has the same effect that inserting a colour bar does once the figure is generated. It makes a colour bar for the bythmetry, not the quake depths. It also changes the bythemetry files somehow and removes topography.

should I include the colour bar inside the for loop?

Walter Roberson 2017-7-20

Note: at the time I wrote the above, there was no public bug report for this issue with scatterm(). The bug report has recently been made public and is https://www.mathworks.com/support/bugreports/1359012

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