[Bf-committers] OT: 3D-Math Question

Remo Pini remo.pini at avexys.com
Thu May 7 19:04:50 CEST 2009

Hi all


I know this might be the wrong place to ask, but with so many brilliant
heads in one spot, I just have to try...


I have an object A and an object B


For each of these objects, I have a translation/location T
(3D-Vector/Vertex), a rotation R (Quaternion) and a Scale S (Float).



Object A: Ta, Ra, Sa

Object B: Tb, Rb, Sb


My problem is the following: Object B's T & R are relative to Object A
and I need to transform them into absolute T & R so that I can calculate
the actual position of each vertex.


I tried some (I thought) obvious things like:


Tb' = (Tb-Ta)*Ra+Ta

Rb' = Ra*Rb


Then for each Vertex Vb of B:


Vb' = (Vb*Sb)*Rb + Tb


However, this seems to be wrong, if I start to rotate Object A around,
the position of Object B relative to Object A changes (which it


What am I doing wrong here?






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