use the 'patch' function with different results (using different matrices)
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Hi! I have two matrices: 'V' and 'trace'.
Using patches with V generates a completely black surface on the figure and I'm fine with it.
When I use the 'trace' matrix the result is different. How come? Is there a way to display 'trace' in the image in the same way as 'V'?
load V
axes1 = axes('Parent',figure);
patch(V(:,1), V(:,2),V(:,3),'k');
view(axes1,[45.7625707544407 8.27114462456761]);
axis equal
%%
load trace
axes2 = axes('Parent',figure);
patch(trace(:,1), trace(:,2),trace(:,3),'r');
view(axes2,[31.7625655339418 23.9174311926605]);
axis equal
3 个评论
Walter Roberson
2023-9-26
Why would you expect that?
Remember that for patch(), points are considered to be ordered
If you sort the original points by angle, and plot the sort order:
load trace
axes3 = axes('Parent', figure);
tc = mean(trace,1);
ang = atan2(trace(:,2) - tc(2), trace(:,1) - tc(1));
[~, order1] = sort(ang);
[~, order2] = sort(order1);
plot(order2)
adjacent points on input bounce back and forth in angle order -- and not even alternately.
figure();
plot(order2(1:50))
采纳的回答
Matt J
2023-9-26
编辑:Matt J
2023-9-26
If you are trying to recover the boundary from a surface triangulation, then,
load trace
[~,P]=freeBoundary(delaunayTriangulation(trace(:,1:2)));
[~,loc]=ismember(P,trace(:,1:2),'rows');
V=num2cell([P,trace(loc,3)],1);
patch(V{:},'k');
view([31.7625655339418 23.9174311926605]);
axis equal
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更多回答(1 个)
Walter Roberson
2023-9-26
In your first patch() call you ask for 'k' -- black -- for the faces. The edge colors default to black as well.
In the second patch() call you ask for 'r' -- red -- for the faces. The edge colors default to black.
The V matrix has coordinates for a simple circle. The trace matrix has much more complex coordinates, going back and forth.
If you were to sort the coordinates then you could get a circle as well. But remember that the coordinates for patch() are ordered so those represent completely different graphing tasks.
load V
axes1 = axes('Parent',figure);
patch(axes1, V(:,1), V(:,2), V(:,3), 'facecolor', 'r', 'facealpha', 0.5, 'edgecolor', 'k');
view(axes1,[45.7625707544407 8.27114462456761]);
axis(axes1, 'equal');
%%
load trace
axes2 = axes('Parent',figure);
patch(axes2, trace(:,1), trace(:,2), trace(:,3), 'facecolor', 'r', 'facealpha', 0.5, 'edgecolor', 'k');
view(axes2,[31.7625655339418 23.9174311926605]);
axis(axes2, 'equal');
axes3 = axes('Parent', figure);
tc = mean(trace,1);
ang = atan2(trace(:,2) - tc(2), trace(:,1) - tc(1));
[~, order] = sort(ang);
patch(axes3, trace(order,1), trace(order,2), trace(order,3), 'facecolor', 'r', 'facealpha', 0.5, 'edgecolor', 'k');
view(axes3,[31.7625655339418 23.9174311926605]);
axis(axes3, 'equal')
1 个评论
Walter Roberson
2023-9-26
Note that if you know you have scattered coordinates, then see also boundary instead of the sorting method I used.
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