Consider a closed contour line (a loop) which crosses the polygonal boundary. Which should happen?
- The contour line ends where it contacts the boundary, leaving the contour open
- The contour line meets and follows the boundary, leaving the contour closed
FWIW, there are a number of ways to get the curve data from a contour plot, but they're all fairly cumbersome. The first output argument contains all the curves in a blockwise format. Each block is arranged in the format [thislevel thisxvalues; blocklength thisyvales]
% an example
z = peaks(100);
[C,hc] = contour(z);
contourlevels = hc.LevelList;
% get vertex sequences from contours
% Vc is a cell array of [x y] vertex lists describing individual curves,
% each column in Vc contains the curves for a particular level
for kl = 1:numel(contourlevels) % index over each level
startidx = find(C(1,:) == contourlevels(kl)); % start of each curve
for kc = 1:numel(startidx) % index over each curve in this level
blockstart = startidx(kc); % the starting index for this block
lenv = C(2,blockstart); % the length of this curve + 1
Vc{kc,kl} = C(:,blockstart+(2:lenv)).'; % C is [level, x; length, y]
end
end
I'm prety sure there are FEX tools to do this more conveniently.
EDIT: possibly relevant:
