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Differences in forms of transformations.

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1) Vector * Transformation => 2nd Vector
2) Transformation * Transformation => 2nd Transformation
3) Transformation + Transformation => 2nd Transformation
4) Vector * (Transformation * Transformation) => 2nd Vector
5) Vector * (Transformation + Transformation) => 2nd Vector

a) What is the difference between 2) + 3)?
b) What is the difference between 4) + 5)?

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[quote name='lucky6969b' timestamp='1343976263' post='4965769']
a) What is the difference between 2) + 3)?
b) What is the difference between 4) + 5)?
[/quote]
[img]http://public.gamedev.net//public/style_emoticons/default/blink.png[/img] Well, one is an addition, the other a multiplication. In [i]3d[/i] math multiplications of transformations are more common, because when you have a homogeneous matrix (most likely your transformation), then the multiplication is like executing the transformation in a sequence.

Extended example:
Take the coffee cup in front of you, you are the center. Now move it away from you (first: translation), then rotate it around youself (second: rotation), and eventually move it closer to yourself (third: translation). This can be described as three transformation matrices:
[i] translation_1[/i]
[i] rotation[/i]
[i] translation_2[/i]

The final trnasformation is
[i]final_transformation = translation_2 * rotation * translation_1[/i]

That is the final position and orientation of your coffee cup [img]http://public.gamedev.net//public/style_emoticons/default/wink.png[/img] Edited by Ashaman73

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To concatenate (append together) transforms, you multiply the matrices together.

Adding two transformation matrices together has no meaning -- the results aren't useful. So, I've never seen (3) and (5) used in a game. Edited by Hodgman

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This topic is 1959 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

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