<DIV>Hello clinton,</DIV> <DIV> </DIV> <DIV>Here is the loop which computes the difference with your suggestions incorporated....</DIV> <DIV> </DIV> <DIV><FONT size=2> <div>vtkMatrix4x4 *pMatrix = vtkMatrix4x4::New();</div> <div>pMatrix->DeepCopy( pOffScreenRenderer->GetActiveCamera()->GetCompositePerspectiveTransformMatrix(1,0,1) );</div> <div>pMatrix->Invert();</div></FONT></DIV> <DIV> </DIV> <DIV><FONT color=#0000ff size=2> <div>for</FONT><FONT size=2>( </FONT><FONT color=#0000ff size=2>int</FONT><FONT size=2> i = 0 ; i < wx ; i++ )</div> <div>{</div> <BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px"> <div></FONT><FONT color=#0000ff size=2>for</FONT><FONT size=2>( </FONT><FONT color=#0000ff size=2>int</FONT><FONT size=2> j = 0 ; j < wy ; j++ )</div> <div>{</div> <BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px"> <div></FONT><FONT color=#0000ff size=2>long</FONT><FONT size=2> index = i * j;</div> <div></FONT><FONT color=#0000ff
size=2>float</FONT><FONT size=2> coons_depth, sphere_depth;</div> <div>displayPoint[0] = i;</div> <div>displayPoint[1] = j;</div> <div> </div> <div></div> <div></FONT><FONT color=#008000 size=2>// get sphere z</div></FONT><FONT size=2> <div>displayPoint[2] = pSphereZBuffer[index];</div> <div>pOffScreenRenderer->SetDisplayPoint( displayPoint );</div> <div>pOffScreenRenderer->DisplayToView();</div> <div>pOffScreenRenderer->GetViewPoint( viewPoint );</div> <div>pMatrix->MultiplyPoint( viewPoint , worldPoint );</div> <div>sphere_depth = worldPoint[2] / worldPoint[3];</div> <div> </div> <div></div> <div></FONT><FONT color=#008000 size=2>// get coons z</div></FONT><FONT size=2> <div>displayPoint[2] = pCoonsZBuffer[index];</div> <div>pOffScreenRenderer->SetDisplayPoint( displayPoint );</div> <div>pOffScreenRenderer->DisplayToView();</div> <div>pOffScreenRenderer->GetViewPoint( viewPoint );</div> <div>pMatrix->MultiplyPoint( viewPoint ,
worldPoint );</div> <div>coons_depth = worldPoint[2] / worldPoint[3];</div> <div></div> <div></FONT><FONT color=#0000ff size=2>double</FONT><FONT size=2> diff = ( sphere_depth - coons_depth );</div> <div>dblSphereVolume += diff;</div></BLOCKQUOTE> <div>}</div></BLOCKQUOTE> <div>}</div> <div></div> <div>printf( "\ncomputed Sphere volume = %f\n" , dblSphereVolume );</div></FONT><BR><BR>Note: forwarded message attached.</DIV><p>
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