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None Help finding the absolute position of an object within another object 

Forum: Geometry
Date: 18 Feb, 2016
From: Chris <Chris>

Hello,

  So I'll get to my question first before going into a bunch of words to
describe my problem more specifically.  The question is, how does Geant4
handle rotations of objects within other rotated objects?  To anyone
willing to take the time to read below, thank you for your time.

  I have, essentially, a two object system.  Within the world volume is a
solenoid placed at an offset in x,y,z and a rotation in x,y relative to the
center of the world volume, this value comes from survey data.  Placed
within that solenoid is a tracking system, which is at some unknown offset
in x,y,z and a rotation in x,y relative to the center of that solenoid.

  Additionally I have from beam data the actual alignment of my tracking
system, which is used for reconstruction purposes, not in Geant 4.

  So my problem is matching up the tracking system in Geant4 with what I
expect to see in real life.  What I have been doing the last few days is to
write out a translation matrix with the offsets and rotations of the
solenoid (taking into account that Geant4 rotates the coordinate frame
rather than the object) and known offsets in position of the tracker in
terms of the world volume, However, when I do this my values appear wildly
off.
Anyone interested can see my work here:
https://docs.google.com/spreadsheets/d/1aNm-ka4OPrwJDw31b1s729Q2zjQFCZGMBVvwf9xGihg/edit?usp=sharing

  I know this because I take residuals between Geant4 Truth positions
verses values I reconstruct against beam alignment.

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