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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Hi<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I was trying to interpolate values at points by locating the containing cell and using the parametric coordinates. The cells are 2d triangles (z==0).<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>It seems to me that the function vtkDataSet::FindAndGetCell does not work as expected!<o:p></o:p></p><p class=MsoNormal>Sometimes points, which are on the edge of a cell are not classified as inside. I am aware that due to numerical precision reasons this is not completely robust, but I would expect that if I increase the Tolerance in the call to FindAndGelCell then I should get a nearby cell. This does not always happen!<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='text-autospace:none'>After digging in the code I see that this function returns a vtkCell if following condition in vtkDataSet::<span style='font-size:9.5pt;font-family:Consolas'>FindCellWalk </span>is fulfilled:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> <span style='color:blue'>if</span> ( (cell->EvaluatePosition(x, closestPoint, subId,<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> pcoords, dist2, weights) == 1)<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> && (dist2 <= tol2) )<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> {<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> <span style='color:blue'>return</span> cellId;<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> }<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'><o:p> </o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>It often happens that cell->EvaluatePosition returns 0 but, the tolerance condition is true. Therefore, the tolerance does not have any effect. I think this should be changed to either:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> <span style='color:blue'>if</span> ( (cell->EvaluatePosition(x, closestPoint, subId,<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> pcoords, dist2, weights) == 1)<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> || (dist2 <= tol2) )<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> {<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> <span style='color:blue'>return</span> cellId;<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> }<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'><o:p> </o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'>Or, alternatively the tolerance should be passed on to the cell and used to evaluate if the point is inside or not. This could for instance be done as follows:<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'><o:p> </o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'>if((pcoords[0] > -tol2) <o:p></o:p></span></p><p class=MsoNormal style='text-indent:.5in;text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'>&& (pcoords[1] > -tol2)<o:p></o:p></span></p><p class=MsoNormal style='text-indent:.5in;text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'>&& (pcoords[2] > -tol2))<o:p></o:p></span></p><p class=MsoNormal style='text-autospace:none'><span style='font-size:9.5pt;font-family:Consolas'> return 1; // i.e. point inside cell<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>