psi constant mode with "PETRA3 P09 EH2" geometry

[prjemian]

Conversation with Fred Picca:

With the "PETRA3 P09 EH2" geometry, how to calculate angles (from h,k,l) when
keeping psi constant?

Yes you need a dedicated psi_constant_mode in order to expresse the psi_constant constraint.

Can the "psi_constant_horizontal" mode be added to the "PETRA3 P09 EH2"
geometry?

I think so, but maybe the best solution would be to create a dedicated feometry for your dedicated diffractometer.
This way we can set the right axes names, sens of rotations of the axes, this way the binoculas-ng
(2D detectors -> h, k, l, qx, qy, qz, q, qpar, qper, etc...) part could be use almost out of the box with your geoemtry.

Is it common for the engines other than "hkl" to be used for operations? Or are
these used for calculations only?

Some peoples use the psi pseudo axis in order to rotate around the Q vector.

some pseudo axes are read/write and others are read only.

Fred

[prjemian]

Conclusion is that we should copy the P09 geometry into our own new one and add the psi_constant_mode to it.

• RUBh_minus_Q_func() is the function that implements similar constraint
• P09 geometry file
• Similar mode definition in E4C