edge colordata property attempts to set are inconsistent

The following section of code works fine when I manually enter them one at a time on the command line, or run the m file with a stop at the set line, and then step past the line.

It doesn't work however if I simply let the m file run completely with a pause. What am I doing wrong?

figure('Position',[166 325 1205 755])
h = plot(gps(:,1),gps(:,2),'r');

spd = a(spdChan).Data(ind);
cmap = colormap;
cmapX = [min(spd):(max(spd) - min(spd))/(size(cmap,1)-1):max(spd)]';
tmp = interp1(cmapX,cmap,spd);
interpCmap = cast([255*tmp 255*ones(size(tmp,1),1)]','uint8');
set(h.Edge, 'ColorType','truecoloralpha', 'ColorBinding','interpolated', 'ColorData', interpCmap);

[Jeff]

As a follow up, I notice the size of the Edge.VertexData matrix no longer has a one to one correspondence with the number of data points in the plot. This seems to happen somewhere above 20,000 data points. I assume there is some function that reduces the number of line segments for efficiency. My issue is this produces an error when I create a ColorData matrix the size of the points used to create the plot, and then attempt to set the ColorData property. How can I reconcile this?

h = plot([0:.001:40],[0:.001:20 19.999:-.001:0])

h = 

    Line with properties:

                Color: [0 0.4470 0.7410]
            LineStyle: '-'
            LineWidth: 0.5000
               Marker: 'none'
           MarkerSize: 6
      MarkerFaceColor: 'none'
                XData: [1x40001 double]
                YData: [1x40001 double]
                ZData: [1x0 double]

    Show all properties

>> h.Edge.get
          AlignVertexCenters: 'off'
             AmbientStrength: 0.3000
                ColorBinding: 'object'
                   ColorData: [4x1 uint8]
                   ColorType: 'truecolor'
             DiffuseStrength: 0.6000
            HandleVisibility: 'off'
                     HitTest: 'off'
                       Layer: 'middle'
                     LineCap: 'none'
                    LineJoin: 'round'
                   LineStyle: 'solid'
                   LineWidth: 0.5000
               NormalBinding: 'none'
                  NormalData: []
                      Parent: [1x1 Line]
               PickableParts: 'visible'
    SpecularColorReflectance: 1
            SpecularExponent: 10
            SpecularStrength: 0.9000
                   StripData: [1 7474]
                     Texture: [0x0 GraphicsPlaceholder]
                  VertexData: [3x7473 single]
               VertexIndices: []
                     Visible: 'on'
       WideLineRenderingHint: 'software'

[Image Analyst]

We don't have gps. We don't have (the badly-named) "a". So how can we run your code to try to reproduce what you're observing?

[Jeff]

here you go, a test m file, when I run it straight through I get a solid blue line, when I put a stop at the set line, then step it, I get the desired color mapped line

clear all
close all

x = [0:.01:20];
y = [0:.01:10 9.99:-.01:0];

h = plot(x,y)

maxcmap = max(y);
mincmap = min(y);
cmap = colormap;
cmapX = [mincmap:(maxcmap - mincmap)/(size(cmap,1)-1):maxcmap]';
tmp = interp1(cmapX,cmap,y);

interpCmap = cast([255*tmp 255*ones(numel(x),1)]','uint8');
set(h.Edge, 'ColorType','truecoloralpha', 'ColorBinding','interpolated', 'ColorData', interpCmap);

[Jeff]

[Jeff]

I'm running 2015b

Answer 1

[Kelly Kearney]

I've found that messing around with some of the undocumented properties of new graphics objects can be finicky, with properties resetting to their original values later, or failing to change when run in a script (as you're seeing). I recommend only resorting to this sort of hacking when you can't find any workarounds using the documented properties.

Luckily, there's an easy workaround for color-changing lines, and it eliminates the need to do the color interpolation manually: use a patch instead.

x = [0:.01:20];
y = [0:.01:10 9.99:-.01:0];
hln = patch([x NaN], [y NaN], [y NaN]);
set(hln, 'edgecolor', 'interp');

[Jeff]

Thanks, I hadn't thought of that. I was also planning on using transparency as a crude 4th dimension. I'll have to research this more to see if I can also control that as well?

[Walter Roberson]

patches support EdgeAlpha and FaceVertexAlphaData properties