Processing 1.0 - Processing Discourse - Behind or in front of a 3d vector

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Index › Programming Questions & Help › Syntax Questions › Behind or in front of a 3d vector

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Behind or in front of a 3d vector (Read 1034 times)

jacob Riiber YaBB Newbies Offline Posts: 6 Copenhagen, Denmark	Behind or in front of a 3d vector Apr 23^rd, 2010, 2:49am Hi I was hoping that someone here could tell me how to investigate if a point is behind or in front of a 3d vector. (Like questioning if a point is above or below a plane, but with only the normal vector known)

davbol

Re: Behind or in front of a 3d vector
Reply #1 - Apr 23^rd, 2010, 7:45am

I'm not sure your question makes sense if interpreted literally as asked. But if I "read into" your question a bit, and assume you mean that your vector is the normal of a plane equation where d == 0, then the sign of "normal dot point" will tell you which side of that plane the point is on. Is that what you're asking?

jacob Riiber

Re: Behind or in front of a 3d vector
Reply #2 - Apr 24^th, 2010, 6:16am

yes I think so. Thank you. And sorry for not making sense

But to be certain: Assuming for instance that my vector is part of a space ship element in a game, where this vector keeps track of the ships orientation in 3d. This could be called the orientation vector. If I want to know if something is in front of that ship, then I:
1. Create a new vector from the ships position (a point) to the point in space I want to investigate
2. Calculate the dot product of the orientation vector and the new vector
3. Look at the sign of the dot product

Is that right?

JohnG Ex Member	Re: Behind or in front of a 3d vector Reply #3 - Apr 24^th, 2010, 7:53am Yup, that's it. If it's >0 it's in front of the ship, <0 behind.

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