HcalBarrel: replace tessellated tiles and end ring with primitive solids - #1108
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Pull request overview
This PR improves HCal Barrel Geant4 navigation performance by replacing several tessellated GDML-based solids (scintillator tiles and the steel end ring) with analytically navigable primitive solids built directly in the geometry plugin.
Changes:
- Replace 16 scintillator tile tessellations with
ExtrudedPolygonsolids using hardcoded boundary vertices and z extents. - Replace the end-ring tessellation with a
Tubeannulus minus 32 cylindrical bolt-hole subtractions, and place the two rings via explicit ±z translations. - Remove
file/url/cacheattributes for tile and end-ring elements from the compact XML (material remains).
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
| src/BarrelHCalCalorimeter_geo.cpp | Builds tile and end-ring geometry from primitive solids instead of loading tessellated GDML. |
| compact/hcal/barrel_gdml.xml | Removes now-unused GDML download attributes for tiles/end ring while keeping materials. |
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Replace 16 scintillator tile tessellations (Tile01-12, CTile09-12) with G4ExtrudedSolid (ExtrudedPolygon) shapes and the barrel end ring tessellation with a G4Tubs annulus minus 32 bolt-hole G4Tubs subtractions. Tessellated solids require the generic navigator to test every facet during boundary crossing, while primitive solids use analytical intersection formulae. Replacing ~1000-vertex tiles (placed >=192 times) and the ~10000-vertex end ring with primitives is expected to give a measurable improvement in navigation speed. Tile shapes (ExtrudedPolygon): - Each tile is a flat 7 mm slab with an 8- or 9-vertex boundary polygon. - Polygon vertex coordinates were extracted from the original tessellation GDML files (stored in eic/epic-data) by tracing boundary edges on the top face. Tile01 retains its non-zero z offset (z: 1.921-8.921 mm) that was baked into the tessellation; all other tiles span +/-3.5 mm. End ring (Tube - 32 x Tube): - Annulus: inner radius 1980.15 mm, outer radius 2619.85 mm, half-length 19.304 mm. - 32 bolt holes: radius 152.4 mm, centres at R = 2293.86069 mm, evenly spaced in phi (11.25 deg pitch). - Previously placed with RotationY(180 deg) to produce the negative-z copy from a shape with z baked in; now placed at +/-3178.406 mm with no rotation (the centred Tube is already reflection-symmetric in z). The GDML file/url/cache attributes for the tiles and end ring are removed from compact/hcal/barrel_gdml.xml; material attributes are retained. The steel sector and chimney-sector tessellations are unchanged. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
er_gdmlfile -> end_ring
tile{N}_gdmlfile -> tile{N}
ctile{N}_gdmlfile -> ctile{N}
These elements no longer reference GDML files; their geometry
is defined inline via <shape> and <dimensions> children.
sec_gdmlfile and csec_gdmlfile are unchanged as they still load
tessellated steel sector shapes from GDML.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
DD4hep's Tube has no (name, rmin, rmax, dz) constructor. The 4-argument template is (rmin, rmax, dz, endPhi). Passing a char const* as the first argument caused the string to be evaluated as rmin, and an empty string "" triggered dd4hep::Evaluator 'blank string detected'. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Summary
Replace 16 scintillator-tile tessellations and the barrel end-ring tessellation in the HCal Barrel geometry plugin with equivalent Geant4 primitive solids, and use daughter-volume placements for the end-ring bolt holes so that Geant4's smart voxelisation applies.
All geometry dimensions are now specified in the compact XML file (
compact/hcal/barrel_gdml.xml) rather than hardcoded in the plugin. No hardcoded data tables remain in the C++ source.Motivation
Tessellated solids force the Geant4 navigator to test every triangle facet at each boundary crossing. The tiles contain several hundred to ~1000 triangles each and are placed ≥192 times per event (12 η layers × 16 φ sectors); the end ring had 9844 vertices and 19816 triangles. Replacing them with primitives removes the facet-loop overhead entirely. For the bolt holes an additional optimisation is possible: using daughter-volume placements instead of a Boolean-subtraction chain lets Geant4's
SmartVoxelHeadervoxelise the 32 holes, giving O(log 32) boundary lookup instead of traversing a depth-32 CSG tree.Changes
Scintillator tiles →
ExtrudedPolygon(G4ExtrudedSolid)All 16 tile shapes (Tile01–Tile12, CTile09–CTile12) are flat 7 mm slabs with an 8–9 vertex boundary polygon. Each tile element in the compact XML now carries a
<shape type="Xtru">child with<twoDimVertex>and<section>sub-elements (following GDML conventions). The plugin reads and constructs anExtrudedPolygondirectly from those elements — no GDML file download is required at runtime.Tile01 retains the non-zero z offset (z: 1.9212–8.9212 mm) that was baked into the original tessellation.
End ring →
Tubemother + 32 airTubedaughtersThe end ring element in the compact XML now carries a
<dimensions>child with attributesrinner,router,zhalf,zcenter,nholes,rhole, andrhole_ctr(all in mm). The plugin reads these and constructs a steel annulus (Tube) with 32 evenly-spaced air-filled bolt-hole daughters.Rather than building a depth-32 Boolean subtraction chain — which Geant4 cannot voxelise — the holes are represented as air-filled daughter
Tubevolumes placed inside the steel annulus mother. A track inside a daughter sees air, which is geometrically equivalent to a hole. Geant4'sSmartVoxelHeaderthen voxelises the 32 daughters, reducing per-boundary work from O(32) (CSG tree) to O(log 32).The two ring copies are placed at z = ±
zcenterwith a simple translation (previouslyRotationY(180°)was used on a shape with z baked in from the tessellation).Compact XML
file/url/cacheattributes removed from tile and end-ring elements. Each tile now has a<shape type="Xtru">child; the end ring has a<dimensions>child.materialattributes are retained. The sector and chimney-sector GDML files are unchanged.Not changed
The steel barrel sector and chimney-sector tessellations (18–21 distinct Z levels, varying XY cross-sections) are left as tessellations pending benchmarking to confirm they are worth the additional implementation effort.