[Gate-users] Autorotation axis issue.

Steven Marsh steven.marsh at canterbury.ac.nz
Mon Apr 27 07:34:35 CEST 2020


Hopefully someone can make sense of this email and assist me to understand how autorotation works when repeating a geometry in a ring.

I am attempting to extend the SPECT example which comes in the gate-exercises using Gate 9.0 with the following amendment ( my amendment is the addition of the third block of code below - the first two blocks are the original code from the example). In the example code a SPECThead object is defined and rotated -90 deg wrt the x-axis of the world volume.  I then attempt to replicate this SPECThead and have them all viewing the centre of rotation for the four heads.

When running my modified code, I get four instances of SPECThead as hoped and in the correct positions however autorotation is not applied as I was expecting. Instead of autorotation causing each of the four heads to "view" the centre of the circle encapsulated by them (centre of rotation in a spect system) they each view in the same direction parallel to the y-axis of the world. Upon closer inspection though, each of the SPECTheads has been rotated but the rotation is about the world's y-axis (although the amount of rotation is consistent with what I was expecting  - albeit about the wrong axis).  It is as though the autorotation is being applied to the z-axis associated with each of the daughter volumes rather than the world - recall the z-axes of each are no longer aligned due to the -90 deg rotation of the first SPECThead.

I have been trying in vain for some time to try and get all four heads to point at the centre of rotation but thus far no luck.  Any advice on where I am going wrong would be much appreciated.


# SPECT Head: main volume, everything is included in SPECThead
# the name MUST be SPECThead - one of available systems is table 1.1
/gate/world/daughters/name SPECThead
/gate/world/daughters/insert box
/gate/SPECThead/geometry/setXLength 57.6 cm
/gate/SPECThead/geometry/setYLength 44.6 cm
/gate/SPECThead/geometry/setZLength 18 cm

/gate/SPECThead/placement/setRotationAxis  1 0 0
/gate/SPECThead/placement/setRotationAngle -90 deg
/gate/SPECThead/vis/setColor white
/gate/SPECThead/setMaterial Air

# Replicate SPECThead to get a multi-headed system
/gate/SPECThead/repeaters/insert ring
/gate/SPECThead/ring/setPoint1 0 0 0
/gate/SPECThead/ring/setPoint2 0 0 1
/gate/SPECThead/ring/setAngularSpan 360. deg
/gate/SPECThead/ring/setRepeatNumber 4

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