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I have a collection of 3D points in the standard $x$, $y$, $z$ vector space. Now I pick one of the points $p$ as a new origin and two other points $a$ and $b$ such that $a - p$ and $b - p$ form two vectors of a new vector space. The third vector of the space I will call $x$ and calculate that as the cross product of the first two vectors.

Now I would like to recast or reevaluate each of the points in my collection in terms of the new vector space. How do I do that?

(Also, if 'recasting' not the right term here, please correct me.)

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Are you sure you are intending x's magnitude to always be the result of the cross product, or only its direction? –  Justin L. Jul 20 '10 at 23:47
    
Enjoy your three identical answers... –  BBischof Jul 21 '10 at 5:52
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2 Answers

up vote 3 down vote accepted

You are changing your basis vectors, call your new ones i, j, and k where i is defined from a-p, j from b-p, and k the cross product. Now recall that your basis vectors should be unit, so take the length of your three vectors and divide the vectors by their length, making i,j, and k unit. Now a = d(a,p)*i, b =d(b,p)*j.

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What you are describing is an Affine Transformation, which is a linear transformation followed by a translation.

We know this because any straight lines in your original vector space is also going to be a straight line in your transformed vector space.

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