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jPCT - a 3d engine for Java => Support => Topic started by: raft on March 12, 2010, 08:03:57 am

Title: rotation by matrix
Post by: raft on March 12, 2010, 08:03:57 am

i have a rotation matrix multiplied by a uniform scale matrix.

* SimpleVector.rotate(matrix) also applies scaling to vector, is this intentional ?
* how can i check rotation part (upper 3x3) of matrix has no scale information ?
* how can i clear scaling from matrix ? assuming i dont know scaling value

thanks

Title: Re: rotation by matrix
Post by: EgonOlsen on March 12, 2010, 08:28:33 am

Yes, that is intentional... ;D


Maybe this works (as long as the scaling is uniform):

• create a SimpleVector of length 1 (for example 1,0,0)
• multiply it with the matrix
• calculate it's length
• if it's not 1, do a scalarMul on the matrix with 1/length

Should work, but might not be the best or fastest way to do it...only a pragmatic way.

Title: Re: rotation by matrix
Post by: raft on March 12, 2010, 08:44:05 am

yes it works, thanks :)

so, assuming there is no translation in matrix, multiplying it with scalar is practically the same as multiplying with a uniform scale matrix. and of course less expensive. i didnt know this

Title: Re: rotation by matrix
Post by: EgonOlsen on March 12, 2010, 08:58:18 am

Just do it once on paper and you'll see... ;)