Issues with legend on a plot?

Question

Darren 2014-4-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/126879-issues-with-legend-on-a-plot

评论： Darren 2014-4-23

So I'm having issues correctly displaying a legend for my figure.

I have an image I'm displaying with ground truths marked in red and text labeled 1-11. Then, I'm wanting to have a legend that displays 1 through 11 vertically with the type of ground truth to the right of it. Unfortunately, I'm getting far, far from this. I would post a screenshot, but I'm technically not allowed to which makes troubleshooting a bit cumbersome.

    h1=figure(1);imagesc(abs(image));set(gca,'YDir','normal');
    hold on
    plot(gnd_TruthY_test,gnd_TruthX_test,'r*');
    text(gnd_TruthY_test,gnd_TruthX_test,num2str(c'),'Color',    [0.859375000000000,0.859375000000000,0.859375000000000],'VerticalAlignment','bottom', ...
                             'HorizontalAlignment','right')
    legend(gt{1,5}(c))

where gt{1,5} contains strings for the ground truth types and c are the indexes that corrspond to the groundtruths in the displayed image.

When I run the above code, my image displays properly but my legend only displays the first ground truth. If I repeatedly click run then the legend eventually builds up. I'm not sure I understand the legend() use in MATLAB >.<

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Darren 2014-4-23

legend(num2str([1:11]','Line %d'))

Worked properly, for the most part, but I still cannot adapt this version to mine.

legend(num2str([gt{1,5}(c)'],'Line %s'))

yields,

Undefined function 'real' for input arguments of type 'cell'.

I'm guessing this is now an issue of the fact that I'm trying to pull info from my cell? This is the part of MATLAB that is the most annoying to me...

Image Analyst 2014-4-23

Don't call your image variable "image" because that is the name of a built-in function.

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Answer 1

Kelly Kearney 2014-4-23

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/126879-issues-with-legend-on-a-plot#answer_134324

在 MATLAB Online 中打开

If I understand your setup correctly, I think the problem is that you want your legend to reference the individual points of a single line object. Is this the sort of thing you're hoping for?

gnd_TruthY_test = rand(1,5);
gnd_TruthX_test = rand(1,5);
c = 1:5;
label = {'one','two','three','four','five'};
figure;
hl = plot([gnd_TruthY_test; nan(1,5)], [gnd_TruthX_test; nan(1,5)], 'r*');
ht = text(gnd_TruthY_test, gnd_TruthX_test, num2str(c'));
legend(hl, label);

If so, the trick is to plot each point to its own line object, which can be accomplished by adding the NaN-padding to each column (causing plot to treat each column as a different line; by default it ignores this convention if both x and y input are vectors).

If that's the case, note that this doesn't really link your legend labels to the text labels next to each point... but perhaps that info is already in your labels?

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Darren 2014-4-23

编辑：Darren 2014-4-23

在 MATLAB Online 中打开

I implemented this via

    h1=figure(1);imagesc(abs(IM));set(gca,'YDir','normal');
    hold on
    hl=plot([gnd_TruthY_test'; nan(1,length(c))'],    [gnd_TruthX_test';nan(1,length(c))'],'r*');
    ht=text(gnd_TruthY_test',gnd_TruthX_test',num2str(c'),'Color', [0.859375000000000,0.859375000000000,0.859375000000000],'VerticalAlignment','bottom', ...
                             'HorizontalAlignment','right')
    legend(hl, gt{1,5}(c)');