Related slack conversation at https://lsstc.slack.com/archives/C9BEJU1T3/p1619128247019600

Bo Xin [X]  - I'm wondering for an example meaning of the `demand`. Are  X, Y = 0, and Z the defocal +/- 1500 micrometers?  If so, what  are U,V,W  ?

those are six DOFs defining the positioning of the hexapod. they are simply (x,y,z,rx,ry,rz). i.e., U is rotation around x-axis, and so on

Following the conversation on slack, I paste the conclusion: "for  the simulated defocal comCam, lsstCam images ,  FOCUSZ would be (0,0,+/-1500, 0,0,0) , and for in-focus images (0,0,0,0,0,0) , while for corner sensors simulated images it would be always (0,0,0,0,0,0) "

Note that for corner sensors it won't be (0,0,0,0,0,0) if the entire camera is pistoned to an off-focus position.

The key point is that the FOCUSZ should simply be the position of the camera hexapod. 

With your simulations, you are using a "MOVE" command to piston the camera. The value that goes with the "MOVE" command should be in the header as FOCUSZ.

 Clarification: `demand` in https://ts-xml.lsst.io/sal_interfaces/MTHexapod.html#demand   is a variable that contains (X,Y,Z,U,V,W) and FOCUSZ  in https://confluence.lsstcorp.org/display/SYSENG/ComCam+Header+Information+Topic+Mapping   is a third element of that variable:  demand[2] . So FOCUSZ is +/- 1500 or 0 . 

The update looks good to me!

Adding FOCUSZ to ts_phosim is included now in Tiago's DM-30128 ticket, marking this one as "Done"