At the SLAC ITk Pixels technical meeting on October 13, 2020, Charlie presented a coordinate system for the ring baseplate. You can find his calculations and coordinate system document at the Indico page here: https://indico.cern.ch/event/960664/
A copy of the coordinate system document is included here as a reference. The calculated coordinates for triplets are the same on either side of the ring, since the rotation of the ring and handling frame accounts for their angular offset. Specifically, the handling frame lines up with a different mark on the base plate. Quads need an additional adjustment, so there are distinct sets of coordinates for the "tubes up" and "tubes down" sides of the rings.
We mount modules in sets using loading bridge pick up tools. Scott's drawings reflect this approach.
The bridges are designed to evade the cooling tubes sticking out of the ring local support. Charlie defined a numbering scheme for the modules in his document. Under this scheme, the modules set in each "wedge" are as follows:
| Triplets | Quads |
|---|---|
9-1-2 3-4-5 6-7-8 | 1-2 3-4 5-6 7-8 9-10 |