Intersection between a Surface and a Line using ARX

By Xiaodong Liang

In the other post, my colleague Philippe introduces how to get intersection between a planar face and a line. In this post, we will see how to get intersection of an arbitrary surface and a line.

ARX provides AcGeCurveSurfInt which  allows you to get intersections of a 3D curve and a surface. AcGeCurveSurfInt  construction method or AcGeCurveSurfInt::Set can input the curve and the surface. While it requires the AcGeSurface. So we need some conversion from AcDbSurface to AcGeSurface. This requires AcBrBrep as the intermediate object.

Following is a small demo code. It asks the user to select a surface and get the intersection of a line (from (0,0,0) to (0,0,1)) and the surface.

Note: The Brep objects are provided by separate include files and lib files. You can find them at: ObjectARX SDK\utilsbrep

static AcGePoint3dArray Intersect(AcDbSurface* pSurface,AcGeLine3d line)    {          AcGePoint3dArray returnPtArray;       AcDbBody* pBody = new AcDbBody();           // 2013      // Acad::ErrorStatus es = pBody->setASMBody(pSurface->ASMBodyCopy());      //before 20123       Acad::ErrorStatus es = pBody->setBody(pSurface->body());            //build AcBrBrep       AcBrBrep* pBrep = new AcBrBrep();       //       if(AcBr::eOk == pBrep->set(*pBody))      {        AcBrBrepFaceTraverser* pFaceTrav = new AcBrBrepFaceTraverser;         if(AcBr::eOk == pFaceTrav->setBrep(*pBrep))       {           for(pFaceTrav->restart();!pFaceTrav->done();pFaceTrav->next())           {            AcBrFace face;                 if(AcBr::eOk == pFaceTrav->getFace(face))            {              double area = 0.0f;             face.getSurfaceArea(area);                  acutPrintf(L"nSurface Area: %f", area);                 //*****whole surface of the Brep face******                      //AcGeNurbSurface nurbSurface;            //face.getSurfaceAsNurb(nurbSurface);            //AcGeCurveSurfInt curveSI;            ////input the curve and line            //curveSI.set(line,nurbSurface);            ////get the count of intersect points            //int count = curveSI.numIntPoints(err_1);            //    if(err_1 == AcGe::kXXOk && count >0 )            //    {                     //        AcGeIntersectError err_2;            //        for(int index = 0 ;index < count; index ++)            //        {            //           AcGePoint3d pt =             //             curveSI.intPoint(index,err_2);                    //            returnPtArray.append(pt);            //        }                    //                    //    }             //**********                 //****real surface of the orignal AcDbSurface                       AcGeExternalBoundedSurface** nurbs = NULL;              Adesk::UInt32 numNurbs = 0;              face.getSurfaceAsTrimmedNurbs(numNurbs,nurbs);              //*****                 for (Adesk::UInt32 i = 0; i < numNurbs; i++)             {                AcGeCurveSurfInt curveSI;                AcGeIntersectError  err_1 = AcGe::kXXOk;                             //input the curve and line                curveSI.set(line,*nurbs[i]);                      //get the count of intersect points                int count = curveSI.numIntPoints(err_1);                if(err_1 == AcGe::kXXOk && count >0 )                {                    AcGeIntersectError err_2;                    for(int index = 0 ;index < count; index ++)                    {                        AcGePoint3d pt =                             curveSI.intPoint(index,err_2);                                returnPtArray.append(pt);                    }                        }                delete nurbs[i];            }            // your responsibility to delete the              // array of surfaces            delete[] nurbs;           }        }      }      delete pFaceTrav;      }      delete pBrep;     
           return returnPtArray;          }    static void getIntersectPts(void)    {          ads_name ename;          ads_point pickpt;               AcDbObjectId objId;         AcDbObject *pObj;              int rc;              // select a surface         rc= acedEntSel(L"nSelect Surface: ", ename, pickpt);              if(rc != RTNORM)         {           if (rc != RTCAN)                 acutPrintf(L"nError selecting entity ");          return;         }              acdbGetObjectId(objId, ename);         acdbOpenObject(pObj, objId, AcDb::kForRead);              AcDbSurface* pEntity1 = AcDbSurface::cast(pObj);              if(!pEntity1)         {              acutPrintf(L"nSelection Invalid...");              pObj->close();              return;         }         // call Intersect         AcGePoint3dArray points =              Intersect(pEntity1,AcGeLine3d(AcGePoint3d(0,0,0),             AcGePoint3d(0,0,1)));         if(points.length() >0)         {             // iterate the points         }              pObj->close();          }