<div dir="ltr"><div><div>Thanks for providing a complete example. It makes it much easrie to help.<br><br></div>Your triangles are not ordered consistently. To see this set the backface property to a different color.<br><br>
</div>#include &quot;vtkProperty.h&quot;<br><br><br>...<br><br><br>  vtkSmartPointer&lt;vtkProperty&gt; back =<br>    vtkSmartPointer&lt;vtkProperty&gt;::New();<br>  back-&gt;SetColor(1,0,0);<br><br>  vtkSmartPointer&lt;vtkActor&gt; actor = vtkSmartPointer&lt;vtkActor&gt;::New();<br>
  actor-&gt;SetMapper(mapper);<br>  actor-&gt;SetBackfaceProperty(back);<br><br><br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Jun 6, 2013 at 10:33 AM, Michele <span dir="ltr">&lt;<a href="mailto:michele.conconi@unibo.it" target="_blank">michele.conconi@unibo.it</a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi everybody,<br>
<br>
I am tring to build a polydata starting from an ordered set of points in<br>
space in order to evaluate its volume.<br>
<br>
I built an exapmple (see below) which generate a correct visual<br>
representation of the polydata, but the computed volume is wrong (6.8 rather<br>
then 48 mm^3).<br>
<br>
I tried aldo the vtkDelaunay2D, with no better results.<br>
<br>
What am I doing wrong?<br>
Thanks in advance for the help<br>
<br>
Michele<br>
<br>
------------------------------<br>
<br>
<br>
#include &lt;vtkVersion.h&gt;<br>
#include &lt;vtkSmartPointer.h&gt;<br>
#include &lt;vtkCellArray.h&gt;<br>
#include &lt;vtkCellData.h&gt;<br>
#include &lt;vtkDoubleArray.h&gt;<br>
#include &lt;vtkPoints.h&gt;<br>
#include &lt;vtkPolyLine.h&gt;<br>
#include &lt;vtkPolyData.h&gt;<br>
#include &lt;vtkPolyDataMapper.h&gt;<br>
#include &lt;vtkActor.h&gt;<br>
#include &lt;vtkRenderWindow.h&gt;<br>
#include &lt;vtkRenderer.h&gt;<br>
#include &lt;vtkRenderWindowInteractor.h&gt;<br>
#include &lt;vtkMassProperties.h&gt;<br>
#include &lt;vtkTriangle.h&gt;<br>
<br>
<br>
<br>
int main( int argc, char *argv[] )<br>
{<br>
        // build the points set to be triangulated<br>
        int Np = 5;<br>
        double **P1, **P2, **P3;<br>
<br>
        P1 = new double*[Np];<br>
        P2 = new double*[Np];<br>
        P3 = new double*[Np];<br>
<br>
        for(int i = 0; i &lt; Np; i++)<br>
        {<br>
                P1[i] = new double[4];<br>
                P2[i] = new double[4];<br>
                P3[i] = new double[4];<br>
        }<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
        {<br>
                P1[i][0]        = 0+i;<br>
                P1[i][1]        = 1;<br>
                P1[i][2]        = 0;<br>
<br>
                P2[i][0]        = 0+i;<br>
                P2[i][1]        = 3;<br>
                P2[i][2]        = 2;<br>
<br>
                P3[i][0]        = 0+i;<br>
                P3[i][1]        = 5;<br>
                P3[i][2]        = 4;<br>
        }<br>
<br>
<br>
        vtkSmartPointer&amp;lt;vtkPoints&gt; points = vtkSmartPointer&lt;vtkPoints&gt;::New();<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
                points-&gt;InsertNextPoint(P1[i]);<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
                points-&gt;InsertNextPoint(P2[i]);<br>
<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
                points-&gt;InsertNextPoint(P3[i]);<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
                points-&gt;InsertNextPoint(P1[i][0],0,P1[i][2]);<br>
<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
                points-&gt;InsertNextPoint(P2[i][0],0,P2[i][2]);<br>
<br>
        for(int i=0;i&lt;Np;i++)<br>
                points-&gt;InsertNextPoint(P3[i][0],0,P3[i][2]);<br>
<br>
<br>
        //build manually the triangle<br>
<br>
        vtkSmartPointer&lt;vtkCellArray&gt; triangles =<br>
vtkSmartPointer&lt;vtkCellArray&gt;::New();<br>
        vtkSmartPointer&lt;vtkTriangle&gt; triangle =<br>
vtkSmartPointer&lt;vtkTriangle&gt;::New();<br>
<br>
        // ------------------------------------- base<br>
        for(int j=3;j&lt;5;j++)<br>
                for(int i = (j*Np)+1; i &lt; (j+1)*Np; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,Np+i-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
        for(int j=4;j&lt;6;j++)<br>
                for(int i = j*Np; i &lt; (j+1)*Np-1; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i+1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,i-Np+1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
<br>
        // ---------------------------------------- side 1<br>
<br>
        for(int i = 1; i &lt; Np; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,3*Np+i-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
        for(int i = 3*Np; i &lt; 4*Np-1; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i+1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,i-3*Np+1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
        // ---------------------------------------- side 2<br>
        for(int i = 2*Np+1; i &lt; 3*Np; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,3*Np+i-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
        for(int i = 5*Np; i &lt; 6*Np-1; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i+1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,i-3*Np+1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
        // ---------------------------------------- side 3<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,0);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,3*Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,4*Np);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,4*Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,5*Np);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,4*Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,0);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,5*Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,2*Np);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,Np);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
        // ---------------------------------------- side 4<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,4*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,5*Np-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,2*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,5*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,6*Np-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,5*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,2*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,Np-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,6*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,3*Np-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,2*Np-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
<br>
<br>
        // -------------------- top<br>
<br>
        for(int j=0;j&lt;2;j++)<br>
                for(int i = (j*Np)+1; i &lt; (j+1)*Np; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i-1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,Np+i-1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
        for(int j=1;j&lt;3;j++)<br>
                for(int i = j*Np; i &lt; (j+1)*Np-1; i++)<br>
                {<br>
                        triangle-&gt;Initialize();<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(0,i);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(1,i+1);<br>
                        triangle-&gt;GetPointIds()-&gt;SetId(2,i-Np+1);<br>
                        triangles -&gt;InsertNextCell(triangle);<br>
                }<br>
<br>
<br>
        // build the polydata<br>
<br>
        vtkPolyData *polyData = vtkPolyData::New();<br>
<br>
        polyData-&gt;SetPoints(points);<br>
        polyData-&gt;SetPolys(triangles );<br>
<br>
<br>
        //evaluate the volume : expected outcome for the current points set 48<br>
<br>
        vtkMassProperties *mass = vtkMassProperties::New();<br>
<br>
        mass-&gt;SetInput(polyData);<br>
        cout&lt;&lt;&quot;volume &quot;&lt;&lt;mass-&gt;GetVolume()&lt;&lt;endl;<br>
<br>
          // Setup actor and mapper<br>
          vtkSmartPointer&amp;lt;vtkPolyDataMapper&gt; mapper =<br>
vtkSmartPointer&lt;vtkPolyDataMapper&gt;::New();<br>
          mapper-&gt;SetInput(polyData);<br>
<br>
<br>
          vtkSmartPointer&lt;vtkActor&gt; actor = vtkSmartPointer&lt;vtkActor&gt;::New();<br>
          actor-&gt;SetMapper(mapper);<br>
<br>
          // Setup render window, renderer, and interactor<br>
          vtkSmartPointer&lt;vtkRenderer&gt; renderer =<br>
vtkSmartPointer&lt;vtkRenderer&gt;::New();<br>
          vtkSmartPointer&lt;vtkRenderWindow&gt; renderWindow =<br>
vtkSmartPointer&lt;vtkRenderWindow&gt;::New();<br>
          renderWindow-&gt;AddRenderer(renderer);<br>
          vtkSmartPointer&lt;vtkRenderWindowInteractor&gt; renderWindowInteractor =<br>
vtkSmartPointer&lt;vtkRenderWindowInteractor&gt;::New();<br>
          renderWindowInteractor-&gt;SetRenderWindow(renderWindow);<br>
          renderer-&gt;AddActor(actor);<br>
<br>
          renderWindow-&gt;Render();<br>
          renderWindowInteractor-&gt;Start();<br>
<br>
return 0;<br>
}<br>
<br>
<br>
<br>
--<br>
View this message in context: <a href="http://vtk.1045678.n5.nabble.com/computing-the-volume-of-a-simple-multi-triangles-polydata-tp5721243.html" target="_blank">http://vtk.1045678.n5.nabble.com/computing-the-volume-of-a-simple-multi-triangles-polydata-tp5721243.html</a><br>

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</blockquote></div><br><br clear="all"><br>-- <br>Unpaid intern in BillsBasement at noware dot com<br>
</div>