Creating a new coordinate system

Support
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20

Thank you @mau_igna_06 this is example works very nicely. It would be probably too long for including it entirely in the script repository but you can upload it into a gist and we can link it from the script repository (as we do it for other longer examples). Gists are version controlled, so you can update the gist and the same link will automatically post to the latest version (and user has access to previous versions of the gist, too).

There are also a few things to fix/improve, such as:

  • Node IDs are not persistent (when you save the scene and load it again a different ID may be assigned to the node), therefore they must never stored in node attributes. Instead, node references can be used, which maintain link between nodes, even if the node IDs change. Since parent transform is already stored using node references, you don’t even need to add another node reference.
  • Simplify the sampling. If ratio=1 then just use the model output and skip the filter. It would be also more relevant to use the VTK9 filter, as VTK8 will not be around for long.
  • Always leave a space after the # character
  • Instead of hardcoding any specific revision, put the method call in a try/except block (put the more recent API in the main path and the old API in the except path), as it is more pythonic and may be faster (not that speed would matter here, just as a general note)
  • Instead of updating the transform in the main path and then implementing it again in onPlaneModified function, just call onPlaneModified once.
  • I would remove the multiple planes support and the i variable to keep things simple.
  • Remove the THIS PART SHOULD ONLY BE COPYPASTED ONCE TILL MARKED comments. It is understood that the entire code snippet is to be executed once. It would just confuse users that they are not allowed to copy-paste some parts.
  • Comment out the …RemoveObserver… line so that if the user copy-pastes the entire code snippet the axes are kept interactive

Two notes for using principal axes of surface mesh points as object coordinate system:

  1. For solid objects Segment Statistics module gives more relevant axis directions. Principal X, Y, Z axes computed by Segment Statistics provides the object’s true principal axes of inertia, based on its volume. PCA of surface mesh points can be quite similar for many shapes, but they are not the same. Even if you sample the surface uniformly, a small feature with a large surface area can throw off the axis directions computed by surface mesh points PCA.

  2. For models that have flat sides (such as CAD models) Segment Statistics module’s oriented bounding box axis directions are more relevant than principal axes. The oriented bounding box axes will not be slightly off if you have small attachments or engravings in the object, but the axes will be generally aligned with flat sides.