[WIP] Tooling with cad files.

Added a converter for tgeo -> step using ROOT's GeoCad library. Right now it seems to generate huge step files. I am not sure if this is a problem for commercial cad software, but FreeCAD certainly struggles with these large files.

examples/scripts/mag_field.cxx

+#include "Math/Vector3D.h"
+#include "Math/Vector4D.h"
+#include "Math/VectorUtil.h"
+#include "TCanvas.h"
+#include "TLegend.h"
+#include "TMath.h"
+#include "TRandom3.h"
+#include "TFile.h"
+#include "TH1F.h"
+#include "TH1D.h"
+#include "TTree.h"
+#include "TF1.h"
+#include "ROOT/TDataFrame.hxx"
+
+#include <vector>
+#include <tuple>
+#include <algorithm>
+#include <iterator>
+
+// DD4hep
+// -----
+// In .rootlogon.C
+//  gSystem->Load("libDDDetectors");
+//  gSystem->Load("libDDG4IO");
+//  gInterpreter->AddIncludePath("/opt/software/local/include");
+#include "DD4hep/Detector.h"
+#include "DDG4/Geant4Data.h"
+#include "DDRec/CellIDPositionConverter.h"
+#include "DDRec/SurfaceManager.h"
+#include "DDRec/Surface.h"
+#include "DD4hep/DD4hepUnits.h"
+
+/** Cell size example.
+ *
+ */
+void mag_field(double z0 = 0.0  ){
+
+  using namespace ROOT::Math;
+  using namespace dd4hep;
+  
+  // -------------------------
+  // Get the DD4hep instance
+  // Load the compact XML file
+  dd4hep::Detector& detector = dd4hep::Detector::getInstance();
+  detector.fromCompact("beamline_test.xml");
+
+  double x_min = -100.0;
+  double x_max =  100.0;
+  double y_min = -100.0;
+  double y_max =  100.0;
+  double z_min = -100.0;
+  double z_max =  100.0;
+  int nx_bins = 200;
+  int ny_bins = 200;
+  int nz_bins = 200;
+  double dx = (x_max -x_min)/nx_bins;
+  double dy = (y_max -y_min)/ny_bins;
+  double dz = (z_max -z_min)/nz_bins; 
+
+  double y0 =  20.0*cm;
+
+  TH2F* hBx = new TH2F("hBx","; z [cm]; x [cm]; B_{x} [T]",nz_bins,z_min,z_max,nx_bins,x_min,x_max);
+  TH2F* hBz = new TH2F("hBz","; z [cm]; x [cm]; B_{z} [T]",nz_bins,z_min,z_max,nx_bins,x_min,x_max);
+  TH2F* hBr = new TH2F("hBr","; z [cm]; x [cm]; B_{r} [T]",nz_bins,z_min,z_max,nx_bins,x_min,x_max);
+  TH2F* hBphi = new TH2F("hBphi","; z [cm]; x [cm]; B_{#phi} [T]",nz_bins,z_min,z_max,nx_bins,x_min,x_max);
+
+
+  for(int ix = 0; ix< nx_bins; ix++) {
+    for(int iz = 0; iz< nz_bins; iz++) {
+
+      double x = (x_min + ix*dx)*cm;
+      double z = (z_min + iz*dz)*cm;
+
+      XYZVector pos{ x, y0, z };
+      XYZVector field = detector.field().magneticField(pos);
+
+      hBz->Fill(z,x,   field.z()/tesla);
+      hBx->Fill(z,x,   field.x()/tesla);
+      hBr->Fill(z,x,   field.rho()/tesla);
+      hBphi->Fill(z,x, field.phi()/tesla);
+    }
+
+    //for(int iy = 0; iy< ny_bins; iy++) {
+
+    //  double x = (x_min + ix*dx)*cm;
+    //  double y = (y_min + iy*dy)*cm;
+
+    //  XYyVector pos{ x, y, z0 };
+    //  XYyVector field = detector.field().magneticField(pos);
+
+    //  hBz->Fill(z,x, field.z()/tesla);
+    //  hBx->Fill(z,x, field.x()/tesla);
+    //  hBr->Fill(z,x, field.rho()/tesla);
+    //}
+  }
+
+  auto c = new TCanvas();
+  c->Divide(2,2);
+
+  c->cd(1);
+  hBz->Draw("colz");
+
+  c->cd(2);
+  hBx->Draw("colz");
+
+  c->cd(3);
+  hBr->Draw("colz");
+
+  c->cd(4);
+  hBphi->Draw("colz");
+
+
+
+}