<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 15 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
span.E-MailFormatvorlage17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:612.0pt 792.0pt;
margin:70.85pt 70.85pt 2.0cm 70.85pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal>Hello,<o:p></o:p></p><p class=MsoNormal>I am experiencing a strange behavior of VTK using its python interface. I am using VTK 8.0.1 and Python 2.7.14 on CentOS7.<o:p></o:p></p><p class=MsoNormal>The base code of my minimum working example is the following:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>import vtk<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>coneSource = vtk.vtkConeSource()<o:p></o:p></p><p class=MsoNormal>coneSource.Update()<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>cone = vtk.vtkPolyData()<o:p></o:p></p><p class=MsoNormal>cone.DeepCopy(coneSource.GetOutput())<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>cone2 = vtk.vtkPolyData()<o:p></o:p></p><p class=MsoNormal>cone2.DeepCopy(cone)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>N = 10<o:p></o:p></p><p class=MsoNormal>for _ in range(N):<o:p></o:p></p><p class=MsoNormal> print cone.GetCell(0).ComputeArea(), cone2.GetCell(0).ComputeArea()<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>What it does:<o:p></o:p></p><p class=MsoNormal>1. It creates a cone 'cone' from a vtkConeSource <o:p></o:p></p><p class=MsoNormal>2. Duplicates it into a 'cone2' and<o:p></o:p></p><p class=MsoNormal>3. accesses the polygon cell at the base of the cone of 'cone' and 'cone2' and evaluates the area.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The for-loop in step 3 shows the strange behavior. With varying 'N' the print statements produces different results. Also whether or not I run this code in PyCharm or in a terminal triggers a different outcome of the print statements.<o:p></o:p></p><p class=MsoNormal>In my IDE the results for different N are the following:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| N | Case | Case2 |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 1 | inf | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 10 | inf | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 80 | OK | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Strangely enough the result also depends on whether or not the following import at the top of the script is present even though its functionality is never used:<o:p></o:p></p><p class=MsoNormal>from vtk.util.numpy_support import vtk_to_numpy<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Then the result is the following:<o:p></o:p></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| N | Case | Case2 |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 1 | nan | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 10 | inf | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 80 | OK | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I also varied the way the vtkConeSource returns its result to 'cone'. If I change the lines <o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>cone = vtk.vtkPolyData()<o:p></o:p></p><p class=MsoNormal>cone.DeepCopy(coneSource.GetOutput())<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>to<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>cone = coneSource.GetOutput()<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The result tables look like this:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| N | Case | Case2 |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 1 | OK | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 10 | (ok) | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>| 80 | (ok) | OK |<o:p></o:p></span></p><p class=MsoNormal><span style='font-family:"Courier New"'>+----+------+-------+<o:p></o:p></span></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>with (ok) meaning that the first print of the for loop prints an incorrect result like inf or nan but the rest of the output is correct.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Note that all other cell areas of the cones are computed correctly (my hunch is that this is due to the fact that the rest of the cells are triangles and not polygons, even though the vtkPolyData object does not distinguish between the two types). Also all the results displayed above are 100% reproduceable on my machine.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>My question to the mailing list is:<br>What I am doing wrong in the creation and copying of my two cones? It appears as if the memory behind the two cones is corrupted in some way. How can I assure that the area calculation is always successful?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Regards<o:p></o:p></p><p class=MsoNormal>Niklas<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>