Use getClosestPointTo() and onSegAt() to locate a polyline vertex near a point

By Wayne Brill

You can use getClosestPointTo() and onSegAt() to find a vertex of a polyline closest to a selected point. Here is an ObjectARX example that shows this idea. To try this run a command that runs this function. If you select a polyline the command line will display the number of the segment of the polyline (where you selected the polyline).

static void TEST_PointOnPoly(void)     {           ads_name ename;      ads_point pt, ptWcs;      AcDbObjectId Id;           if(acedEntSel(_T("Select Pline: "),                          ename,pt)!=RTNORM)       return;           // Convert to WCS incase selection was made       // while in a UCS.      acdbUcs2Wcs(pt, ptWcs, Adesk::kFalse);       acdbGetObjectId(Id,ename);      AcDbEntity* pEnt;      acdbOpenObject(pEnt,Id,AcDb::kForRead,false);           AcDbPolyline* pLine=NULL;      pLine=AcDbPolyline::cast(pEnt);           if(!pLine)      {       acutPrintf(_T        ("Selected Entity not a Polyline"));       pEnt->close();       return;      }           AcGePoint3d clickpt;      // This will convert the pick point to a       // point on the polyline      pLine->getClosestPointTo(asPnt3d(ptWcs), clickpt);      // Convert to 2d point, needed below...       AcGePoint2d clickpt2d(clickpt.x, clickpt.y);            for(unsigned int c=0; pLine->numVerts() > c ; c++)      {       double segParam;       // This is the test filter here...it uses the        // nifty API onSegAt       if(pLine->onSegAt(c, clickpt2d, segParam))         {        acutPrintf(_T("Selected Segment: %d n"),c+1);        break;       }      }      pLine->close();     }