The two attached plots show before and after adding the final HEPI Y to RZ Cross Coupling factor.
This was first looked in alog 40106, 40117, & 40150 for ETMX. I want to look at ETMX again as that was before I looked at the geometric consideration I posted earlier in 41955.
I feel pretty good about the solution here though now.
The optical lever out put during the HEPI length stroke is the sum of actual optic yaw plus the expected apparent yaw due to the OpLev Length to Yaw Cross Coupling: OLOutput = Actual + Expected.
So I want to minimize the Actual = Output - Expected. Assume in this case the Actual is all caused by the HEPI Cross Coupling. See the 40106 alog for the conversions and such to get the units, and the amplitudes of the OpLev Cross Coupling factors are from E1200836. The signs of these corrections are subject to geometric analysis.
Anyway, with a CC factor for HEPI Y to RZ of 0.0065 in H1:HPI-ETMY_IPSALIGN_3_2 of the IPS Alignment Matrix, the residual is pretty much zero'd out as seen in the 2nd plot although I might be able to tweak it a little bit more.
This length drive on the ETMY HEPI is 0.8mm so a huge drive wrt anything we'd ever need to drive but why not get rid of it.
Re; "I want to look at ETMX again as that was before I looked at the geometric consideration I posted earlier in 41955." I've looked at that again in light of the geometry and conclude my result is valid for ETMX. The bottom line for this exercise is that the OpLev Length to Angle CC factor is Positive for ETMX (hence my correctness) and it is negative for ETMY. This is because the PD is on the opposite side of the beam tube and the beam is displaced in the opposite direction with a positive path length change. Thank you for your support.
Went ahead and did the ETMY X to RZ HEPI diagonalization. A value of -.0064 for H1:HPI-ETMY_IPSALIGN_3_1 does a thorough job of minimizing the cross-coupling. This has been accepted into SDF.