crop the polygon from the 3D surface

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Mammadbaghir Baghirzade 2020-6-18

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编辑： Mammadbaghir Baghirzade 2020-11-10

采纳的回答： darova

Hi all,

I have such an attached 3D surface and a polygon on it. (Code is provided below)

I aim to crop the portion which is only inside the polygon and delete everything outside the polygon.

I found out the function of "inpolygon", but it did not work well enough since it is for 2D.

Then I encountered with "inpolyhedron" which is written for 3D, but was not that successfull on using it.

Is there any other way that you would suggest?

Thank you

Regards

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Kelly Kearney 2020-6-18

It's difficult to tell from the picture... does all the data (both the surface and polygon) fall along a single plane?

Mammadbaghir Baghirzade 2020-6-18

编辑：Mammadbaghir Baghirzade 2020-6-18

Hi Kelly,

Thank you for your reply.

Yes, there are 5 points on the surface and then I joined those points with lines.

So, both of the polygon and the surface are on the same plane.

I've provided the script in the main question part.

Thanks you

Regards

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darova 2020-6-19

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https://ww2.mathworks.cn/matlabcentral/answers/550906-crop-the-polygon-from-the-3d-surface#answer_454105

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What about this? I just cutted surface in 2d plane

[X1,Y1,Z1] = sph2cart(llambda1,pphi1,6.9);
surf(X1,Y1,Z1)
in = inpolygon(X1,Y1,xl1,yl1);
view(3);
hold on
plot3(X1(in),Y1(in),Z1(in),'.r')
plot3(xl1, yl1, zl1,'MarkerSize',14, 'Color','red')
axis vis3d

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Kelly Kearney 2020-6-19

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Darova beat me to the answer...

Your points don't actually fall on a plane, but rather on a lightly-curved surface. You can crop the data as desired by projecting in onto a 2D plane. That's what Darova's call to inpolygon does, by ignoring the z-coordinates... projects the surface and polygon coordinates onto the XY plane.

And as to how they figured out rr1 = 6.9, if one assumes the polygon vertices fall on the same surface:

[~,~,r] = cart2sph(xl1,yl1,zl1)
r =
          6.9          6.9          6.9          6.9          6.9          6.9

Mammadbaghir Baghirzade 2020-6-19

编辑：Mammadbaghir Baghirzade 2020-6-19

Hi Kelly,

Thanks for your explanations, I understand.

Do you know how can I connect those points (vertices of a polygon) with an arc instead of a line.

I mean , now I understand better what you meant by asking if the surface and the polygon are on the same plane or not.

Atually I want to crop the portion which looks like a polygon from the surface, so I need to have the curvature.

In this case, I assume there is not a curvature, do you agree with me?

Thanks

Regards

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MATLAB Graphics 2-D and 3-D Plots Surfaces, Volumes, and Polygons Surface and Mesh Plots

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