How to Plot A 3D Ring of any given shape?

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Sushmitha Kudari 2020-2-22

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https://ww2.mathworks.cn/matlabcentral/answers/507017-how-to-plot-a-3d-ring-of-any-given-shape

评论： Walter Roberson 2020-2-23

Say for example I have a 2D matrix that makes a simple shape like a star, rectangle or circle. How can I take this 2D shape and turn it into a 3D ring? If it was a star, a star shaped ring, if its a square, a square shaped ring and so on...

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Jacob Wood 2020-2-23

Would you like to extrude your 2D shape into a 3D shape? And what is the intended result? A plot of this object or just a matrix description?

Sushmitha Kudari 2020-2-23

I would like to first make a 3d matrix of it and then plot it as a point cloud. Yes I would like to extrude a 2D shape into a 3D one.

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Answer 1

Walter Roberson 2020-2-23

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Create a reference set of vertices centered around 0, 0, and a description of faces joining them. I suggest using something compatible with patch()

Now translate the reference point out to what would correspond to angle 0 in the ring.

Now iterate.

Use makehgtform to create a transform matrix that would describe rotating (relative to the origin) by the appropriate angle for this iteration.

Now apply the transform matrix to the reference vertex coordinates by matrix multiplication, keeping them in the same relative order. Record the rotated coordinates for your point cloud. Usethe rotated coordinates and the previously constructed face information to patch() the rotated object into visual existence.

After all of the iterations, use the recorded vertices to patch() into place faces joining each rotated object to its adjacent rotated object -- the skin of the ring.

If your object being rotated has no internal structure such that the skin is all you care about then you can skip the patch() as you iterate, just using the list of final coordinates to build the skin.

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Sushmitha Kudari 2020-2-23

Could you show me an example of how to do this with a simple matrix like this

xy = [4 0; 8 1; 4 2; 1 9; 3 4];

Walter Roberson 2020-2-23

Not without writing the code for you. The algorithm I set out should be enough for you to create the point cloud of the ring. Once you have done that part then we will look more closely at the challenges of drawing a solid around the point cloud.

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