[Halld-offline] reading SC geometry

[Craig Bookwalter]

Hi folks,
    I'm trying to write a couple of routines that match hits in the SC 
to tracks in the FDC and CDC, and I am stuck on getting the geometry out 
from HDDS. Using jgeomread, I see a tempting section:

[snip]
/HDDS/StartCntr_s/section/pgon[@comment='start counter scintillator' and 
@materi
al='Scintillator' and @name='STRC' and @profile='-4.500000 9.000000' and 
@segmen
ts='1' and @sensitive='true']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.322573 7.623501 
0.000000']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.322573 7.623501 
50.000000']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.322011 7.623501 
50.009194']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.292758 7.594248 
50.487477']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.285948 7.592000 
50.524220']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.203756 7.509808 
50.967688']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.180759 7.496290 
51.040625']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.056895 7.372426 
51.433472']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='7.007656 7.338360 
51.541516']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='6.854363 7.185067 
51.877886']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='6.767627 7.120563 
52.019427']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='6.599181 6.952118 
52.294306']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='6.483595 6.850960 
52.459379']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='2.010570 2.377935 
58.847522']
/HDDS/StartCntr_s/section/pgon/polyplane[@Rio_Z='2.257075 2.257075 
59.020127']
[end snip]

But I don't know how to read this out from the examples on the wiki, 
since these polyplanes have no attribute names like `paddle1' or 
something. I suppose I could do something like:

Get("//StartCntr_s/section/pgon/polyplane[@Rio_Z='7.322573 7.623501 
0.000000']", sc_planes_vec)

but it seems lame to have to hard-code the positions. Also, I noticed 
that the TOF and FDC read their geometry from a "composition" section 
rather than a polyplane -- perhaps I shouldn't even be reading out the 
polyplanes, but I don't see a similarly tempting composition section for 
the start counter. All I really want is a point in the plane and a 
normal vector for each start counter paddle, so I can follow Dave's 
recipe with the DMagneticFieldStepper, so any guidance in that direction 
would be greatly appreciated. Thanks in advance!

--cb


-- 
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 Craig Bookwalter			FSU Office:  (850) 644 3808
 Department of Physics			JLab Office: (757) 269 5465
 Florida State University		craigb at hadron.physics.fsu.edu
 Tallahasse, FL 32306			craigb at jlab.org		


"One toke? You poor fool. Just wait till you see those (expletive) bats."
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