Have you tried vtkExtractSelectedFrustum? <br><br><div><span class="gmail_quote">On 3/6/07, <b class="gmail_sendername">Michael Knopke</b> <<a href="mailto:Michael.Knopke@gmx.de">Michael.Knopke@gmx.de</a>> wrote:</span>
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<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;" lang="DE">Hi,</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;" lang="DE"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">I'm trying to write a new vtk-filter that can crop-out
(set scalars to fixed value e.g. 0) selected volumes (e.g. inside of
BoxWidget).</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Unlike all other cropping filter I know, will this filter
work with vtkImageData and preserve topology and geometry. This means it will
not cut cells.</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Therefore I'm trying to implement frustum culling
(with the planes from BoxWidget) and later add octree to speed up calculation.</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">The problem I have is regarding detection if the point that
is evaluated lies behind the plane. As far as I know, one has to calculate:</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">1). Shortest distance to plane (this works well) </span></font><font face="Wingdings" size="2"><span style="font-size: 10pt; font-family: Wingdings;">
à</span></font><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> returns PlanePointDistance</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">2). Add this distance to the DotProduct of ( PointX,
NormalOfPlane):</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> Result = PlanePointDistance + (vtkMath::Dot(PointX,
Normal));</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">3). If result is negative than pointX lies behind Plane</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Unfortunately this yields wrong results. Does anybody know
what's wrong?</span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;"> </span></font></p>
<p><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Michael</span></font></p>
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