problem with convhulln degenerate
显示 更早的评论
Hi my name is noé alvarado I want to find de convex hull of the next point:
xyzw = [1 -1 -1.375 0;-0.5 -0.8 -0.2830 0;-1.3 0.7 0.217 0;1.5 1.3 1.74 0;0.6 0 0 0]
xyzw =
1.0000 -1.0000 -1.3750 0
-0.5000 -0.8000 -0.2830 0
-1.3000 0.7000 0.2170 0
1.5000 1.3000 1.7400 0
0.6000 0 0 0
tess = convhulln(xyzw)
however i have the error:
Error using ==> qhullmx The data is degenerate in at least one dimension - ND set of points lying in (N+1)D space.
Could yoyu help me?
thanks
回答（4 个）
Nshine
2020-1-16
xyzw = [1 -1 -1.375 0;-0.5 -0.8 -0.2830 0;-1.3 0.7 0.217 0;1.5 1.3 1.74 0;0.6 0 0 0]
convhulln(xyzw)
The error occurs because the last column is all zeros. If you delete the last column and try again:
xyzw(:,4) = [];
convhulln(xyzw)
you get the answer
ans =
1 4 3
4 2 3
2 1 3
1 2 4
ie: facet 1 is made by the triangle connecting vertex 1, 4 and 3, etc.
Image Analyst
2012-3-20
0 个投票
I'm not sure I understand. You have a 2D matrix. Why not use the 2D version of convex hull, convhull()?
And what is "the next point"? What were the prior points for that matter?
You can't have the convex hull of just a point - you need at least 3 points to give a meaningfull convex hull.
1 个评论
Nshine
2020-1-16
This is an old thread, but the the argument for convhulln, X is an m-by-n array (ie: 2D array) representing m points in n-D space, as can be read in the documentation:
help convhulln
Hi everybody,
even keeping the last column , you could try this way:
xyzw = [1 -1 -1.375 0;-0.5 -0.8 -0.2830 0;-1.3 0.7 0.217 0;1.5 1.3 1.74 0;0.6 0 0 0]
convhulln (xyzw, {'QJ'})
2 个评论
Walter Roberson
2020-1-28
The last column of xyzw is all 0.
ilPlus30
2020-1-28
Sorry you're right, however in that way the last column could go on, for example it could be important not to delete it.
Shannu
2020-9-18
what id degeneracy of matrix
A=[-1 0 0 0
0 -1 0 0
0 0 -1 0
0 0 0 -1];
1 个评论
Walter Roberson
2020-9-18
You have 4 points in a 4 dimensional space. In order to generate a convex hull, you need at least 5 points for a 4 dimensional space.
类别
在 帮助中心 和 File Exchange 中查找有关 Bounding Regions 的更多信息
2020-9-18
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
