How to add new output variables in Hits

[matclim]

Greetings,
I've been writing a sandwich calorimeter using scintillator bars and passive material and wish to have the layer and bar number in the simulation output. To that effect I've so far been using the x y z truth information from the G4 output but would like something more handy in preparation for digitisation. Is it possible to add this information directly in the output? If so how can one do that?

Cheers,
matclim

[MarkusFrankATcernch]

Hi,

you will have to do the following:

1. instrument the pathes to the sensitive volumes with so-called physical volume ids.
   Volume::addPhysVolID("layer",<number>) You have to do this starting from the sub-detector assembly all the way down to
   the sensitive. The products (aka the concatenation) of the the volume ids to the sensitive must be unique cross all
   possible pathes.
2. You have to define a readout segmentations which uses all the volume tags you use ("layer", "bar", etc.).
   There are plenty of examples there. The width of the field in bits is defined by the biggest volume id you use.
   If you overrun, you will get error messages when building the volume manager. These error messages you MUST take seriously.
3. You need to instantiate first the dd4hep the volume manager and secondly the volume manager of DDG4
   (which actually happens automatically).
4. Then you start: The sensitive detectors in DDG4 will compute for each hit the cellID and store it together with the hit.
   This cellID can then be used (together with the DD4hep volume manager) to access the proper transformation of the cell
   volume to the world or the the subdetector coordinate frame.

That's it. OK. sounds simpler than it is, but once you got the pathes all unique, most of the job is done.
Cheers,

Markus

[MarkusFrankATcernch]

@matclim did you succeed with the instructions above ?

[matclim]

Not quite, I assign each bar (Box) volume a unique name:

for( int ix=0; ix < widebar_num_x; ++ix )  {
    xpos += x_widebar.x()/2.;
    PlacedVolume pv = det_wide_layerbox_vol.placeVolume(widebar_vol, Transform3D(rot,Position(xpos, 0e0, 0e0)));
    pv.addPhysVolID("splitcal_bar", volumecode);
    volumecode++;

and place each of these volumes in a layer:

for( int iz=0; iz < num_z; ++iz )  {

[...]

PlacedVolume pv_det = detbox_vol.placeVolume(det_wide_layerbox_vol, Transform3D(rot_layers,Position(0,0,z_layer)));
pv_det.addPhysVolID("splitcal_layer", iz);

With the readout being as such:

<readout name="SplitCalWideBarHits">
      <segmentation type="CartesianGridXY" grid_size_x="6*cm" grid_size_y="6*cm" offset_x="-108*cm" offset_y="-108*cm"/>
    <id>system:8,splitcal_bar:6,splitcal_layer:6,x:22,y:22</id>
    </readout>

but cannot see any splitcal_bar or splitcal_layer in my output (here in a TBrowser)

Any idea what I am doing wrong?