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I use a plane to cut the mesh through meshcut and get a cut surface. The contour of this section is represented by discrete points, how can I get the perimeter of this contour?

The profile of this section is similar to an ellipse but not a regular shape.Could you give me some advises to compute the perimeter or have you found some code about perimeter computation in meshcut?

More details: Here are the points I got from meshcut. They can be viewed as two-dimensional points. How can I get the convex hull of these discrete points and calculate the perimeter of the convex hull? enter image description here

daisy
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  • Please provide enough code so others can better understand or reproduce the problem. – Community Dec 18 '22 at 23:16
  • I have tried to use opencv (cv2.fitEllipse(2d coordinates of points)), but I got the error: cv2.error: OpenCV(4.6.0) /io/opencv/modules/imgproc/src/shapedescr.cpp:355: error: (-215:Assertion failed) n >= 0 && (depth == CV_32F || depth == CV_32S) in function 'fitEllipseNoDirect' – daisy Dec 20 '22 at 14:49

1 Answers1

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You have added the trimesh tag, so I'm going to suggest a very simple solution using this library applied to the Stanford bunny.

Here is our bunny:

enter image description here

Load it (I'm also adding type hints):

mesh: trimesh.base.Trimesh = trimesh.load_mesh(r"path\to\bunny.ply", process=False, maintain_order=True)

We can take a three-dimensional cross-section using a plane by specifying its normal and a point:

section: trimesh.path.Path3D = mesh.section(
    plane_origin=[0.0, 0.0, 30.0], plane_normal=[0.0, 0.0, 1.0]
)

We can convert this three-dimensional cross-section to a two-dimensional one.

section_2d: trimesh.path.Path2D = section.to_planar()[0]

Let's plot it. As you can see, it's clearly a non-convex shape:

plt.scatter(section_2d.vertices[:, 0], section_2d.vertices[:, 1])
plt.show()

enter image description here

You can get the perimeter of the section as follows:

section_2d.length
>>> 251.61385868533435
blunova
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