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# 3D trig (?) problem...

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I''m working with bones in a 3D engine. I''d like to derive the endpoint of any given bone, based on the start point, the angle (or angles, really; it''s a vector), and the length. My dim and distant memories of various math classes make me feel like this is a relatively basic problem, but I can''t seem to figure out what to do. Given some time, sleep, and perusal of old text-books, I''m sure I''ll figure it out... but if there''s anyone who can just give me the answer off the top of their head, or even point me in the direction of a relevant online tutorial, I''d appreciate it.
"Sweet, peaceful eyelash spiders! Live in love by the ocean of my eyes!" - Jennifer Diane Reitz

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there is no single 'angle', you have 3 angles:
x angle, y angle, and z angle.

Generate a Y axis rotation matrix, an X axis rotation matrix, and a Z axis rotation matrix, and multiply them in this order:

(Y * X) * Z, then multiply the resulting matrix by the point to get the final endpoint.

EDIT: I partially take that back, because you can rotate about an arbitrary axis using a single angle. However, I firmly believe that in this case using matrix mathematics is much better. I can post the equation for rotation about an arbitrary axis if you want me to.

[edited by - Shadow12345 on February 6, 2004 1:13:51 PM]

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Edit: Although I couldn't get the method you described to work properly, I've found a way around the problem entirely.

Thank you for your help, regardless.

"Sweet, peaceful eyelash spiders! Live in love by the ocean of my eyes!" - Jennifer Diane Reitz

[edited by - Logodae on February 9, 2004 5:01:25 PM]

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Umm, well, it does work, that''s what I use, just make sure you check the following:

-Make sure you are using the matrices for the corrrect coordinate system you are using (OpenGL uses a right hand coordinate system I believe)
-Make sure you multiply the Y rotation matrix by the X rotation matrix, GET A RESULTING MATRIX, and then multiply the RESULTING matrix by the Z axis rotation matrix, to get the final matrix that represents the rotation about the X, Y and Z axes.
-Make sure you are multiplying the matrices together properly - the [row][column] element of the final matrix should be equal to the product between the row and column of the two matrices you are currently multiplying together, and in order to multiply two matrices together the number of columns of the second must equal the number of rows of the first matrix

That''s the only useful info I can think of that you might''ve done wrong.

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