将凸包转换为二进制掩码 [英] Converting convex hull to binary mask

问题描述

我想生成一个二进制掩码，它对于所有体素来说都是一样的，对于体积之外的所有体素来说都是零。体积由一组三维坐标（<100;一些坐标位于体积内）的凸壳限定。

我可以得到凸包使用 CONVHULLN ，但是如何将其转换为一个二进制掩码？

如果没有好的方法可以通过凸包，您是否有其他想法可以创建二进制掩码？

解决方案

您可以使用 DelaunayTri class 和 pointLocation 方法。下面是一个例子：

  pointMatrix = rand（20,3）; ％＃一组20个随机三维点
 dt = DelaunayTri（pointMatrix）; ％＃创建Delaunay三角剖分
 [X，Y，Z] = meshgrid（0：0.01：1）; ％＃为你的卷创建一个坐标网格
 simplexIndex = pointLocation（dt，X（:)，Y（:)，Z（:)）; ％＃查找单纯形索引
％＃每个点在
掩码内=〜isnan（simplexIndex）; ％＃在凸包外的点有一个
％＃单纯形索引NaN 
 mask = reshape（mask，size（X））; ％＃将面具重新塑造成101×101×101 
  

上面的例子创建了一个逻辑对于101×101×101的网格，单位体积（每个维度0到1）的掩模，对于三维点集的凸包内的网格点，具有1（真） p>

I want to generate a binary mask that has ones for all voxels inside and zeros for all voxels outside a volume. The volume is defined by the convex hull around a set of 3D coordinates (<100; some of the coordinates are inside the volume).

I can get the convex hull using CONVHULLN, but how do I convert that into a binary mask?

In case there is no good way to go via the convex hull, do you have any other idea how I could create the binary mask?

解决方案

You can solve this problem using the DelaunayTri class and the pointLocation method. Here's an example:

pointMatrix = rand(20,3);       %# A set of 20 random 3-D points
dt = DelaunayTri(pointMatrix);  %# Create a Delaunay triangulation
[X,Y,Z] = meshgrid(0:0.01:1);   %# Create a mesh of coordinates for your volume
simplexIndex = pointLocation(dt,X(:),Y(:),Z(:));  %# Find index of simplex that
                                                  %#   each point is inside
mask = ~isnan(simplexIndex);    %# Points outside the convex hull have a
                                %#   simplex index of NaN
mask = reshape(mask,size(X));   %# Reshape the mask to 101-by-101-by-101

The above example creates a logical mask for a 101-by-101-by-101 mesh spanning the unit volume (0 to 1 in each dimension), with a 1 (true) for the mesh points inside the convex hull of the 3-D point set.

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