Centroid of a 3D Alphashape object

Hello everyone. I have obtained a three-dimensional reconstruction of an object by exploiting matlab's alphaShape function.

Does anyone know an effective way to calculate its centroid?

Important notes: the figure is highly irregular and the distribution of the points that make up the object is heterogeneous.

Answer 1

[Moksh]

Hi Alfredo,

After creating an ‘alphaShape’ object in MATLAB, you can perform geometric queries like accessing all the boundary points.

You can use the ‘Points’ property of ‘alphaShape’ function to get the set of all the boundary points.

Now you can simply use your desired approach to calculate the centroid using these coordinates. One method is to use the ‘ploygonCentroid3d’ function of the ‘geom3d’ library. Please note that you need to download this library for the ‘ploygonCentroid3d’ function to work. Here is an example code for this.

% Generating 1000 random 3d coordinates
x = rand(1000, 1);
y = rand(1000, 1);
z = rand(1000, 1);

% Generating the 3-dimensional irregular construction from the above
% coordinates using alphaShape function
shp = alphaShape(x, y, z);
plot(shp)

% Accessing the points from the alphaShape object
coord = shp.Points;

% Computing the centroid
centroid = polygonCentroid3d(coord)

For further understanding of the ‘alphaShape’ and accessing the ‘geom3d’ library please refer to the following documents.

alphaShape - https://in.mathworks.com/help/matlab/ref/alphashape.html

geom3d - https://in.mathworks.com/matlabcentral/fileexchange/24484-geom3d

Please know that the package mentioned above is not maintained by MathWorks.

Hope this helps!