U-Solids: new geometrical primitives library for Geant4 and ROOT Marek Gayer CERN Physics Department (PH) Group Software Development for Experiments (SFT)

Introduction, motivation Two geometry modellers in ROOT and Geant4 Solids are 80% of maintenance effort in geometry modeller Consolidate algorithms into a single, new U-Solids library Introduce few new solid shapes Optimized, adapted to new architectures 1/19/20162

Solids to be implemented Union of all solids from Geant4 and ROOT –Simple solids (e.g. box, tube, cone, trapezoid) - mostly ported from the existing implementation, used to provide an initial set for tests within the new library –Complex existing solids (e.g. polycone, extruded polygone) - to be consolidated in the new library (one of the priorities) New solids to optimize existing use cases: union of many solids using voxelization techniques The ordering of implementation is to be decided. 31/19/2016

Currently implemented solids For the start, the simplest shapes were selected Box, Orb (done), Trapezoid (ongoing) 1/19/20164

Navigation functionality and library services for each solid Performance critical methods: –Location of point either inside, outside or on surface –Shortest distance to surface for outside points –Shortest distance to surface for inside points –Distance to surface for inside points with given direction –Distance to surface for outside points with given direction –Normal vector for closest surface from given point Additional methods: Bounding Box, Capacity, Volume, Generating points on surface/edge/inside of solid, Creating mesh for visualization … 51/19/2016

Criteria of inclusion of new and existing codes from Geant4, ROOT Validity of returned results Performance Readability, simplicity of algorithm Possibility of easy vectorization Caution about not introducing new errors 1/19/20166

Suite of tests U-Solids codes should pass: –Optical test –Solid Batch Test (SBT)  Original geometry and voxel tests  Results comparison test  Performance test –ROOT tests (Todo) 1/19/20167

Optical Escape Optical photon is generated inside solid Repeatedly bounces from inner surface Particle must not escape the solid 1/19/20168

Solids Batch Test (SBT) geometry and voxel tests Random points test (groups of inside, outside and surface points) Various distance type methods are tested by numerous checks E.g. for each inside random point p, SafetyFromInside(p) must be > 0 It also tests random voxels with random inside points 1/19/20169

Solids Batch Test (SBT) performance and results comparison tests Attempt to compare performance of Geant4, ROOT and new U-Solids Similar performance as one indicator of correct implementation of new methods Also, values and their differences from different codes can be compared Plots are used for quick evaluation Work in progress Todo: port and measure in Linux 101/19/2016

Example plot: performance test 11 1/19/2016 Note: preliminary results, to be validated on Linux with standard compilation flags

Example plot: Results comparison test 121/19/2016

Future work Tests consolidation Finish trapezoid based on test results From other simple solids up to the more complex ones Continue work on union of many solids Polycone is very often used and has room for improvement 1/19/201613

Acknowledgment Part of AIDA project, coordinated by Gabriele Cosmo Definition / steering in collaboration with Andrei Gheata and John Apostolakis Other contributors: –Jean-Marie Guyader - Multi-union implementation (summer student) –Tatiana Nikitina - Geant4 integration and testing 141/19/2016

151/19/2016 Thank you for your attention. ?????? Do you have any questions ?