Calculating the area related to a specific color in colormap
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how to calculate the area of only the grey zone (less than 0.5) of this colormap?
2 Comments
DGM
on 26 Jun 2023
It would probably be a lot more sensible to start from the data instead of trying to disassemble a figure to get the data back again.
Answers (1)
DGM
on 26 Jun 2023
You might want to double check this.
openfig figure1.fig;
hp = get(gca,'children');
% CData in this case is 121834x3
% that is one color for each vertex of 121834 triangles
% the rendered color is interpolated linearly from the vertices
C = hp.CData;
% for the purposes of demonstration, i'm going to just assume
% that faces with _average_ vertex CData < 0.5 are to be selected
faceinROI = mean(C,1)<0.5;
% get only those selected faces
faces = hp.Faces(faceinROI,:);
% calculate the sum of the areas of those triangles
a = hp.Vertices(faces(:,2),:) - hp.Vertices(faces(:,1),:);
b = hp.Vertices(faces(:,3),:) - hp.Vertices(faces(:,1),:);
c = cross(a,b,2);
totalarea = 1/2 * sum(sqrt(sum(c.^2, 2)))
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