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Example: the clustering methods

In this article an example of different clustering methods is showed and discussed. The scene below is used to explain the different clustering method. In the scene there are 3 shampoo bottles next to each other, 4 boxes randomly on top of each other and 4 electrical plug shieldings separated from each other.  A snapshot of this scene can be downloaded here.

../../_images/Clustering-2d.png ../../_images/Clustering-points.png

Touching parts

These methods look at the change of surface. If a surface change is too abrupt it is considered as a separate cluster. On the image below the results of this clustering method is shown. For the shampoo bottles three different clusters are formed which is good. For the boxes, the 2 boxes that are aligned but under an angle are not clustered apart. The transition of the surface is to smooth to filter them apart. For the electrical plug shieldings multiple clusters per part are formed, which is not good.

Best results for:

  • Rounded parts

  • Cylinders: bottles, gas springs, steel bars,..

  • Balls: tennis balls, oranges,..

../../_images/Clustering-touching.png

Plane Based Clustering

This method looks for flat surfaces in the scene. If two surfaces have a different orientation they are considered as separate clusters. On the image below the results of this clustering method is shown. For the shampoo bottles multiple clusters are formed, which is not good. For the boxes all of the boxes are clustered apart andno points are missing at the edges of the surfaces, which is good. For the electrical plug shieldings multiple clusters per part are formed, which is not good.

Best results for:

  • Flat surfaces

  • Boxes

../../_images/Clustering-plane-based.png

Non-touching parts

This method groups points into cluster that are close together. Objects are clustered apart if there is a physical gap. On the image below the results of this clustering method is shown. For the shampoo bottles one big cluster is formed, which is not good. Also the two aligned boxes are not clustered apart. For the electrical plug shieldings, which are positioned separated, one cluster per part is formed, which is good.

Best results for:

  • (Complex) shapes that are separated

../../_images/Clustering-non-touching.png