Resolve geometry conflict

I used a union shape envelope for resolving the geometry conflict.

src/ForwardRICH_geo.cpp

@@ -143,18 +143,26 @@ static Ref_t createDetector(Detector& desc, xml::Handle_t handle, SensitiveDetec
     auto mcpMat = desc.material(mcp.materialStr());
 
     // an envelope for the detector
+    // use a complicated shape to avoid conflict with the other parts
+    // cone for radiator and the first set of mirrors
     double halfLength = 0.5 * (mirZ + 5.0*cm);
-    double rmin = std::min(pRmin, tRmin);
-    double rmax = std::max(std::max(pRmax, tRmax2), tRmax1);
+    double rmin = tRmin;
+    double rmax = tRmax2;
     for (xml::Collection_t sl(mir, _Unicode(slice)); sl; ++sl) {
         auto mRmin = sl.attr<double>(_Unicode(rmin));
         auto mRmax = sl.attr<double>(_Unicode(rmax));
         if (mRmin < rmin) { rmin = mRmin; }
         if (mRmax > rmax) { rmax = mRmax; }
     }
-    Tube envShape(std::max(0., rmin - 0.1*cm), rmax + 0.1*cm, halfLength, 0., 2*M_PI);
+    rmin = std::max(0., rmin - 0.1*cm);
+    Cone env1(halfLength, rmin, tRmax1 + 0.1*cm , rmin, rmax + 0.1*cm);
+    // disk for detection plane
+    Tube env2(std::max(0., pRmin - 0.1*cm), pRmax + 0.1*cm, pThick + 0.1*cm, 0., 2.*M_PI);
+
+    UnionSolid envShape(env1, env2, Position(0., 0., pZ + pThick/2.));
+
     Volume envVol(detName + "_envelope", envShape, desc.material("AirOptical"));
-    envVol.setVisAttributes(desc.visAttributes(detElem.visStr()));
+    // envVol.setVisAttributes(desc.visAttributes(detElem.visStr()));
 
     // ---------------
     // Gas radiator container and spherical mirrors inside it