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description: GSI Helmholtzzentrum für Schwerionenforschung
items: Geometry Problems
items: Re: Geometry Problems

Geometry Problems
type: item
description: Hello everybody, I wanted to inform you about a problem we have been dealing with the last week concerning our lumi detector geometry. Since this can also affect many other detector subsystems I wanted to share this with you. After an update of the fairroot (FairRoot-v-15.03) and external packages (mar15), we discovered that our 2 dimensional angular acceptance all of a sudden showed almond like shaped inefficiencies on the edges of our modules. We analyzed the situation and came to the conclusion that this effect arises from the geometry not being constructed or simulated as we wanted. We have 10 modules aligned around the beampipe in circle. Each module consists of a diamond support and cooling structure having glued on 5 MuPix sensors on its front and 5 more on this back face. The problem was that the diamond structure was constructed from a circle (or complete tube segment) and then being cut to the appropriate dimensions via a CompositeShape. 876 // ****************************** cvd cooling support discs ************************ 877 // the cvd disc shape 878 TGeoTube* shape_cvd_disc = new TGeoTube("shape_cvd_disc", 0., 879 cvd_disc_rad, cvd_disc_thick_half); 880 // The inner beam pipe defines the inner acceptance region for the cvd cut_out 881 TGeoTube* shape_cvd_cutout_inner = new TGeoTube("shape_cvd_cutout_inner", 882 0., inner_rad, 1.); 883 // finally cvd discs will be cut at the left and right down to 36 degree in phi 884 // for that we subtract tube segments 885 TGeoTubeSeg* shape_cvd_disc_cut_side = new TGeoTubeSeg( 886 "shape_cvd_disc_cut_side", 0., outer_rad, 1., 887 +delta_phi / 2. / pi * 180., 888 -delta_phi / 2. / pi * 180.); 889 // before: cvd disc was moved to the displaced position around the z axis 890 // now: segments for the cut are moved off centered and cvd disc remains in the center 891 TGeoRotation* cvd_rotation = new TGeoRotation("cvd_rotation", 0, 0, 0); 892 TGeoTranslation* cvd_translation = new TGeoTranslation("cvd_translation", 893 -c…
creator: Stefan Pflueger
date: 2016-04-19T12:47:11-00:00

Re: Geometry Problems
type: item
description: Dear Stefan, last September I reported you several geometry warnings which were coming from the luminosity monitor, making the simulation crash sometimes in my Mac. Is this problem you found connected to these issues?
creator: StefanoSpataro
date: 2016-04-20T11:54:07-00:00

Re: Geometry Problems
type: item
description: Hi Stefano, I checked the forum and my emails but I could not find the problem you are referring to. Do you have any link for me? It could be that that there is some relation to what you mentioned, but I don't know the exact warnings you are referring to so kind of difficult to tell. Since I only changed the way the diamond support structure is created and it looks completely identical at the end I would assume there should be no connection... But in case ppl are using the CompositeShape to construct parts of their geometry I strongly suggest to check if their similar effects as we have observed them. Our angular resolution at 1.5 GeV is now twice as good as before! The effect was dramatic.
creator: Stefan Pflueger
date: 2016-04-20T12:04:15-00:00

Re: Geometry Problems
type: item
description: StefanoSpataro wrote on 14 September 2015 16:42 Dear all, after a long delay I put the QA macros inside macro/qa/lmd. I reduced the number of events to 1000 since it is too slow and in some computer it took more than 6 minutes for 2000. In reality, I noticed that sometimes the sim macro is crashing and I have not understood why. In particular in my MAC I was not able to run the macros, it crash at event 0. When I am able to run, there are several geant4 errors from the geometry: -------- WWWW ------- G4Exception-START -------- WWWW ------- *** G4Exception : GeomNav1002 issued by : G4PropagatorInField::ComputeStep() Particle is stuck; it will be killed. Zero progress for 51 attempted steps. Proposed Step is 1.99896e-05 but Step Taken is 1.99896e-05 in volume lmd_vol_cvd_disc *** This is just a warning message. *** -------- WWWW -------- G4Exception-END --------- WWWW ------- -------- WWWW ------- G4Exception-START -------- WWWW ------- *** G4Exception : GeomNav1002 issued by : G4PropagatorInField::ComputeStep() Particle is stuck; it will be killed. Zero progress for 51 attempted steps. Proposed Step is 1.74027e-05 but Step Taken is 1.74027e-05 in volume lmd_vol_vac *** This is just a warning message. *** Then maybe the geometry has internal problems. Doing a CheckFullGeometry I found the following: ==================================================================== STAGE 2: Global overlap/extrusion checking within 10 microns ==================================================================== Info in <TGeoNodeMatrix::CheckOverlaps>: Checking overlaps for cave and daughters within 0.001 Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_ref_sys with 2 daughters but not voxelized Check overlaps: [==========] 1589 [100.00 %] Info in <TGeoNodeMatrix::CheckOverlaps>: Number of illegal overlaps/extrusions : 12 and ==================================================================== STAGE 3: Propagating 1000000 tracks starting from vertex and conting number of boundar…
creator: StefanoSpataro
date: 2016-04-20T12:08:38-00:00

Re: Geometry Problems
type: item
description: Hi, thx! Ok that looks indeed like these problems could be connected. Crash means the whole simulation is aborted, right? If so I never experienced this in my simulations... The errors seem like they could be coming from the strange geometry we had before. lmd_vol_cvd_disc is exactly the volume that was troublesome... would be interesting to see if these messages disappear now. I did a CheckFullGeometry() now and the only bad things I got is these warnings: Quote: Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_vac with 9 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_ref_sys with 2 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_half with 4 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_plane with 6 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_module with 3 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_side with 3 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_die with 6 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_die with 4 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_side with 3 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_die with 6 daughters but not voxelized Warning in <TGeoChecker::CheckOverlaps>: Volume lmd_vol_die with 4 daughters but not voxelized Im not sure how bad this is... what does the voxelized mean? At least the diamond support seems not to be part in it. Everything else looks clean. I just had a thought, maybe our mistake was setting the cut shape thicknesses to 1. in the old geometries. That is kind of unnecessary and could introduce some problems...
creator: Stefan Pflueger
date: 2016-04-20T13:39:20-00:00

Re: Geometry Problems
type: item
description: When you have a volume with daughters, the modeler creates for each volume some optimization structures called voxels (see Voxelization) to minimize the penalty having too many daughters in your tracking performance. I.e. in a structure where you have many daughters, such as a pixel layer, or a chambers with thousands of wires, to find in which volume the point (x,y,z) is located (you have to imagine a loop into all the daughter volumes). If I remember correctly, the warning appears when the bounding box of an assembly is smaller than the inside volumes. In any case, the warning reflects some anomaly in the geometry, virtual or non virtual overlaps of clashes. Have you tried to take a look into such volumes, to understand what could be the possible reason? Which lmd geometry are you checking?
creator: StefanoSpataro
date: 2016-04-28T11:58:49-00:00

Re: Geometry Problems
type: item
description: Hi, no I did not check the volumes in detail... Is that a critical issue? My simulations work fine and the results now look much better. I'm using the Lumi_Detector geometry file in the trunk geometry folder. Stefan
creator: Stefan Pflueger
date: 2016-04-28T13:34:38-00:00

Re: Geometry Problems
type: item
description: Hi, I have just tried macro/qa/lmd/sim_LMD.C and in my mac it still crashes at the first event: ### Run 0 start. >>> Event 0 *** Break *** segmentation violation Generating stack trace... [invalid usage]: unrecognized option '-d' Usage: atos [-p pid] [-o executable] [-f file] [-s slide | -l loadAddress] [-arch architecture] [-printHeader] [address ...] 0x000000010e131f97 in _ZNK17TGeoShapeAssembly15DistFromOutsideEPKdS1_idPd + 0x447 from /Users/spataro/fairsoft_mar15p1bis/buildFairSoft/lib/root/libGeom.so [invalid usage]: unrecognized option '-d' Usage: atos [-p pid] [-o executable] [-f file] [-s slide | -l loadAddress] [-arch architecture] [-printHeader] [address ...] 0x000000010e131e38 in _ZNK17TGeoShapeAssembly15DistFromOutsideEPKdS1_idPd + 0x2e8 from /Users/spataro/fairsoft_mar15p1bis/buildFairSoft/lib/root/libGeom.so [invalid usage]: unrecognized option '-d' Usage: atos [-p pid] [-o executable] [-f file] [-s slide | -l loadAddress] [-arch architecture] [-printHeader] [address ...] 0x000000010e10554c in _ZN13TGeoNavigator24FindNextDaughterBoundaryEPdS0_Rib + 0x8bc from /Users/spataro/fairsoft_mar15p1bis/buildFairSoft/lib/root/libGeom.so [invalid usage]: unrecognized option '-d' Usage: atos [-p pid] [-o executable] [-f file] [-s slide | -l loadAddress] [-arch architecture] [-printHeader] [address ...] 0x000000010e103a96 in _ZN13TGeoNavigator16FindNextBoundaryEdPKcb + 0x9c6 from /Users/spataro/fairsoft_mar15p1bis/buildFairSoft/lib/root/libGeom.so [invalid usage]: unrecognized option '-d' Usage: atos [-p pid] [-o executable] [-f file] [-s slide | -l loadAddress] [-arch architecture] [-printHeader] [address ...] 0x000000012317d8cd in _ZN16TG4RootNavigator11ComputeStepERKN5CLHEP10Hep3VectorES3_dRd + 0x3dd from /Users/spataro/fairsoft_mar15p1bis/buildFairSoft/lib/libg4root.so This means there is still something bag in the geoemtry definition, or maybe the file in the qa macro is obsolete.
creator: StefanoSpataro
date: 2016-04-28T14:42:09-00:00