Checking for a point inside a region of a spherical surface

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zeeshanzia84

Joined: 29 May 2006
Posts: 202
Helped: 19
Location: Pakistan / Germany

21 Jun 2008 11:33 Checking for a point inside a region of a spherical surface

Hi everybody,

I am working on a 3D Morphing algorithm.

I have a point X on lying on a unit sphere in the spherical coordinate system. I have three other points A,B, and C which are also on the unit sphere.

I need to find out whether X lies on the spherical surface enclosed by A,B, and C or not.

Can any one tell me how to do this?

Thanks a lot in advance.

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elmolla

Joined: 14 Jul 2005
Posts: 133
Helped: 16

23 Jun 2008 15:16 Re: Checking for a point inside a region of a spherical surf

I don't get you, do you mean in MATLAB for example or generally?

zeeshanzia84

Joined: 29 May 2006
Posts: 202
Helped: 19
Location: Pakistan / Germany

23 Jun 2008 17:04 Re: Checking for a point inside a region of a spherical surf

I needed a mathematical procedure to do this, so I could implement this in C++.

I know how to do it now. Here's how:

Calculate three planes. Each one is defined by three points: 2 of your "spherical triangle" points and the center of your sphere. Have the normals of the planes pointing "inwards" on your spherical triangle. The space inside those three planes defines your spherical triangle. Check your test point against the planes; if it's on the side of the plane where the normal is pointing, it's inside your spherical triangle.