Instrument definition, facing

When defining a new instrument, we had problems with the default

We have panels of detector tubes, place the panels a (0,0,0), but
give specific (x,0,z) positions of vertical tubes of pixels, which have
different (0,y,0) locations.
With the facing default some panels show a weird geometry.
Should we define the facing only for pixels - which makes the .xml
file bigger?
What is the meaning / reason of

to be found in many intrument files?

eh, hem, the input form did not support direct input of angle brackets…
I meant the line
< components-are-facing x=“0.0” y=“0.0” z=“0.0” />
< facing val=“none”/>

I don’t fully understand what you are attempting to do, but get the impression that the instrument you want to construct is like MERLIN and suggest you look at its IDF. It has tubes placed in polar coordinates within the location elements. Cartesian coordinates can be used instead.

Thanks for the tip, EXED indeed is similar to MERLIN.
It works, if every pixel has a < facing x=“0” y=“0” z=“0” />
markup, but fails if I only use the components-are-facing default.

MERLIN uses that ‘facing’ 0,0,0 element for each tube. The pixels are defined using a ‘locations’ element in the definition of each tube type with no ‘facing’ elements.