GMT module orientations (from Richard Majka):
(click on the image for a full [large!] size version)




GMT module positions within TOF trays (from Bill Llope, email to the stargmt mailing list on 2012-10-31):

here's some info on the gem global positioning in gemtof trays.
note that these are *nominal* positions. The most important
slop contributions to these are as follows
- in the Z direction, the trays are positioned to ~1/4" roughly.
Determining the tray Z-positions, and inputting this info
to the star dB, is part of the standard offline calibrations
every year. This algorithm will need to be modified for these
trays given the lack of info from modules 1-4 and 29-32.
OTOH, there will now be much more precise spacepoints available
from the gems!
- in the R-phi directions, there are several sources of 10-20 mil
offsets (feet vertical gap, feet width, rail positioning, etc). 
Additional information can be found here:
http://wjllope.rice.edu/~TOF/TOF/Documents/TOF_Tolerances.pdf

As far as i can tell, the GEM fiducial is precisely centered
in *phi* in a TOF tray. 

Richard has used the high-phi, low-eta, corner of a gem as
his origin, and provided the position of this origin in the
Z-phi plane with respect to GINO and/or the "big hole". 
Using the big hole corner to translate the numbers:
dZ_origin = 1.589-0.525 = 1.064"

From my CADD files of the TOF trays, this GEM origin in |Z| is
thus nominally
position 1 (|eta|~0): Z = 1.665 + 1.064 = 2.729"
position 8 (|eta|~1): Z = 76.740 + 1.064 = 77.768"

again - this is the high-phi, low-|eta| corner of the gems
not their centroid (as e.g. geant would want).

In R...
82.642          (top surface of TPC rail, 209.91cm)
+ (3.050-0.30)  (bottom assy to upper pem nut)
+ (1.300-0.75)  (top assy from lower through hole)
-------------
85.942"

with richard's offset of 0.336", the R-center of the gem fiducial
is then at 85.606"

let me know if this is unclear or you need more details
bill

  -Gene