[vtkusers] Rendering/Computing normals of a surface

Bill Lorensen bill.lorensen at gmail.com
Sat Apr 20 10:21:31 EDT 2013 

A simpler approach is to create another polydata that just contains the
points and normals you want to display. Run this polydata through the glyph
filter and display the results along with the original polydata.



On Fri, Apr 19, 2013 at 1:19 PM, Bill Lorensen <bill.lorensen at gmail.com>wrote:

> Here is an example that uses ProgrammableGlyphFilter
> http://vtk.org/Wiki/VTK/Examples/Cxx/Visualization/ProgrammableGlyphFilter
>
>
>
> On Fri, Apr 19, 2013 at 1:17 PM, Bill Lorensen <bill.lorensen at gmail.com>wrote:
>
>> The number of normals msu match the number of points. Off the top of my
>> head, you might be able to use the
>> // .NAME vtkProgrammableGlyphFilter - control the generation and
>> placement of glyphs at input points
>> // .SECTION Description
>> // vtkProgrammableGlyphFilter is a filter that allows you to place a
>> glyph at
>> // each input point in the dataset. In addition, the filter is
>> programmable
>> // which means the user has control over the generation of the glyph. The
>> // glyphs can be controlled via the point data attributes (e.g., scalars,
>> // vectors, etc.) or any other information in the input dataset.
>> //
>>
>>
>>
>> On Thu, Apr 18, 2013 at 6:04 AM, Kilgus, Thomas <
>> t.kilgus at dkfz-heidelberg.de> wrote:
>>
>>> Hi Bill,****
>>>
>>> ** **
>>>
>>> that worked out well. Now my normals have the correct color. ****
>>>
>>>  ****
>>>
>>> I am still struggling how I could visualize a Subset of normals of my
>>> surface. I can select the normal subset like this:****
>>>
>>> ** **
>>>
>>>     vtkSmartPointer<vtkFloatArray> normals =
>>> vtkSmartPointer<vtkFloatArray>::New();****
>>>
>>>     normals->SetNumberOfComponents(3);****
>>>
>>>      vtkSmartPointer<vtkIdList> IDs = //a containing about 200 IDs of
>>> all normals I would like to see****
>>>
>>>       for(int j = 0; j < IDs->GetNumberOfIds(); ++j)****
>>>
>>>       {****
>>>
>>>           normals->InsertNextTuple(
>>> normalGenerator->GetOutput()->GetPointData()->GetNormals()->GetTuple(IDs->GetId(j))
>>> );****
>>>
>>>       }****
>>>
>>> ** **
>>>
>>> However, if I set these normals for my polydata and try to render
>>> everything a crash occurs inside the Update() of the glyph3d. I assume that
>>> the glyph3d is struggling, because I insert a polydata with 300k points and
>>> add only 200 normals. ****
>>>
>>> ** **
>>>
>>> I could also select the corresponding 200 points from the polydata and
>>> make a new polydata containing 200 points and 200 normals. Is this the
>>> “optimal” way to go?****
>>>
>>>
>>> Regards****
>>>
>>> Thomas****
>>>
>>> ** **
>>>
>>> *From:* Bill Lorensen [mailto:bill.lorensen at gmail.com]
>>> *Sent:* Montag, 15. April 2013 18:47
>>>
>>> *To:* Kilgus, Thomas
>>> *Cc:* vtkusers at vtk.org
>>> *Subject:* Re: [vtkusers] Rendering/Computing normals of a surface****
>>>
>>> ** **
>>>
>>> Have you set the ScalarRange on the Mapper? You should set it to the
>>> range of your scalar data. If you do not want to display scalar colors,
>>> apply SetScalarVisibilityOff() to your mapper.****
>>>
>>> ** **
>>>
>>> ** **
>>>
>>> On Mon, Apr 15, 2013 at 11:51 AM, Kilgus, Thomas <
>>> t.kilgus at dkfz-heidelberg.de> wrote:****
>>>
>>> Hey Bill,****
>>>
>>>  ****
>>>
>>> I just figured out that the normals of my Kinect data are indeed there.
>>> They are just rendered very small and in dark blue on a black renderwindow.
>>> I set the color of the actor to red and don’t use the SetColorMode method
>>> of the glyph3d (I tried to use it, but it didn’t change anything). The
>>> normals of my ball are rendered in red. Do you have any idea why my Kinect
>>> data has blue glyphs and ignores all color calls? Does this “blue” have any
>>> meaning? ****
>>>
>>>  ****
>>>
>>> Regards,****
>>>
>>> Thomas****
>>>
>>>  ****
>>>
>>> *From:* Bill Lorensen [mailto:bill.lorensen at gmail.com]
>>> *Sent:* Freitag, 12. April 2013 16:44****
>>>
>>>
>>> *To:* Kilgus, Thomas
>>> *Cc:* vtkusers at vtk.org
>>> *Subject:* Re: [vtkusers] Rendering/Computing normals of a surface****
>>>
>>>  ****
>>>
>>> The mapping is 1:1. There will be a normal for each point and a normal
>>> for each cell.****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>> On Fri, Apr 12, 2013 at 10:30 AM, Kilgus, Thomas <
>>> t.kilgus at dkfz-heidelberg.de> wrote:****
>>>
>>> Sorry, either this example is not the answer to my question or I don’t
>>> get it :). ****
>>>
>>>  ****
>>>
>>> I have N normals inside a vtkDoubleArray and V vertices inside a
>>> vtkPolyData. How can I get the corresponding normal(s) N(j) to vertex V(i).
>>> I think i != j, because when splitting is on NumberOfNormals !=
>>> NumberOfVertices, or not? In other words, the mapping is NOT 1:1. ****
>>>
>>>  ****
>>>
>>> The example simply adds 3 normals to 3 points and here the mapping is
>>> 1:1.****
>>>
>>>  ****
>>>
>>> *From:* Bill Lorensen [mailto:bill.lorensen at gmail.com]
>>> *Sent:* Freitag, 12. April 2013 16:21****
>>>
>>>
>>> *To:* Kilgus, Thomas
>>> *Cc:* vtkusers at vtk.org
>>> *Subject:* Re: [vtkusers] Rendering/Computing normals of a surface****
>>>
>>>  ****
>>>
>>> Look at this example:****
>>>
>>> http://vtk.org/Wiki/VTK/Examples/Cxx/PolyData/PolyDataPointNormals****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>> On Fri, Apr 12, 2013 at 9:04 AM, Kilgus, Thomas <
>>> t.kilgus at dkfz-heidelberg.de> wrote:****
>>>
>>> And how would I get the normal of a certain vertex? Especially with
>>> SplittingOn()****
>>>
>>>  ****
>>>
>>> *From:* Bill Lorensen [mailto:bill.lorensen at gmail.com]
>>> *Sent:* Freitag, 12. April 2013 14:57****
>>>
>>>
>>> *To:* Kilgus, Thomas
>>> *Cc:* vtkusers at vtk.org
>>> *Subject:* Re: [vtkusers] Rendering/Computing normals of a surface****
>>>
>>>  ****
>>>
>>> 2) vtkPlaneSource generates normals. Many of the source's do.****
>>>
>>>  ****
>>>
>>> After****
>>>
>>>  normalGenerator->Update();****
>>>
>>> try****
>>>
>>> normalGenerator->GetOutput()->Print(std::cout);****
>>>
>>> to see if there are normals present****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>> On Fri, Apr 12, 2013 at 8:45 AM, Kilgus, Thomas <
>>> t.kilgus at dkfz-heidelberg.de> wrote:****
>>>
>>> Unfortunately, that is a bit complicated and inside our own framework.
>>> But basically, this happens:****
>>>
>>>  ****
>>>
>>> vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();**
>>> **
>>>
>>> points->SetDataTypeToDouble();****
>>>
>>> vtkSmartPointer<vtkCellArray> polys =
>>> vtkSmartPointer<vtkCellArray>::New();****
>>>
>>>  ****
>>>
>>> for loop for all pixels of the depth image****
>>>
>>> {****
>>>
>>> Insert 3d point into points****
>>>
>>>  ****
>>>
>>> Insert cell points for valid (!=0) points with valid neighbors (simple
>>> triangulation)****
>>>
>>> }****
>>>
>>>  ****
>>>
>>> vtkSmartPointer<vtkPolyData> mesh = vtkSmartPointer<vtkPolyData>::New();
>>> ****
>>>
>>> mesh->SetPoints(points);****
>>>
>>> mesh->SetPolys(polys);****
>>>
>>>  ****
>>>
>>> We also add texture coordinates and scalars, but this is not related to
>>> normals, is it?****
>>>
>>>  ****
>>>
>>> You can see the details here:
>>> http://mitk.org/git/?p=MITK.git;a=blob;f=Modules/ToFProcessing/mitkToFDistanceImageToSurfaceFilter.cpp;h=2b24b193315c2db97bce1d4f8aed90df42c99d1f;hb=HEAD
>>> ****
>>>
>>>  ****
>>>
>>> My questions 3. and 4.  are not related to the Kinect data, are they?***
>>> *
>>>
>>>  ****
>>>
>>> Regards,****
>>>
>>> Thomas****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>> *From:* Bill Lorensen [mailto:bill.lorensen at gmail.com]
>>> *Sent:* Freitag, 12. April 2013 14:36
>>> *To:* Kilgus, Thomas
>>> *Cc:* vtkusers at vtk.org
>>> *Subject:* Re: [vtkusers] Rendering/Computing normals of a surface****
>>>
>>>  ****
>>>
>>> How are you creating your Kinect mesh?****
>>>
>>>  ****
>>>
>>> On Fri, Apr 12, 2013 at 8:28 AM, Kilgus, Thomas <
>>> t.kilgus at dkfz-heidelberg.de> wrote:****
>>>
>>> Hi everyone,****
>>>
>>>  ****
>>>
>>> I’m trying to compute and render normals of certain vertices of a mesh
>>> (in fact a Kinect mesh). I assume that I have to compute the normals via
>>> vtkPolyDataNormals and display them using a vtkGlyph3d? ****
>>>
>>>  ****
>>>
>>> I observed some strange behavior which really confused me:****
>>>
>>>  ****
>>>
>>> 1.       If I create a vtkPlaneSource or load a ball from hard disc and
>>> compute normals for that data, everything seems fine. If I load an “open”
>>> surface (my Kinect mesh), there are no normals displayed. The documentation
>>> says that SetAutoOrientNormals does only work with closed surfaces. But at
>>> the moment I don’t care about orientation. There should be normals for at
>>> least some vertices of an open mesh, shouldn’t there?****
>>>
>>> 2.       If I load my Kinect mesh and make a new polydata which
>>> contains as much points at (0,0,0) as I have normals and set the normals
>>> for the new polydata, the glyph will produce arrows pointing from (0,0,0)
>>> to somewhere. This looks pretty good could but could be a random result
>>> with empty memory. ****
>>>
>>> 3.       If I connect my vtkPlaneSource or the ball directly to the
>>> glyph (I skip the vtkPolyDataNormals), normals are still rendered
>>> correctly. Does this mean my vtkPlaneSource already contains them from the
>>> beginning? Are they computed in the background somewhere inside the
>>> glyph3d? Is the vtkPolyDataNormals even necessary? This only works for the
>>> plane and the ball - not for the Kinect mesh. I can imagine that a plane
>>> automatically computes its normal on Update(), but why does my ball have
>>> normals already?****
>>>
>>> 4.       How can I get the normal of a certain vertex Id? If I use
>>> vtkFloatArray::SafeDownCast(output->GetPointData()->GetNormals()) are Id’s
>>> equal to the vertex Id’s of the polydata? What happens if I turn splitting
>>> on and get multiple normals for each vertex? How is the mapping done?***
>>> *
>>>
>>>  ****
>>>
>>> My code looks as follows:****
>>>
>>>  ****
>>>
>>> vtkSmartPointer<vtkPolyData> inputPolyData = //load some data****
>>>
>>>  ****
>>>
>>>   // Generate normals****
>>>
>>>   vtkSmartPointer<vtkPolyDataNormals> normalGenerator =
>>> vtkSmartPointer<vtkPolyDataNormals>::New();****
>>>
>>>   normalGenerator->SetInput( inputPolyData );****
>>>
>>>   normalGenerator->ComputePointNormalsOn();****
>>>
>>>   normalGenerator->ComputeCellNormalsOff();****
>>>
>>>   normalGenerator->SetSplitting(0); //I want exactly one normal per
>>> vertex****
>>>
>>>   normalGenerator->Update();****
>>>
>>>  ****
>>>
>>>   vtkSmartPointer<vtkPolyDataMapper> mapperNormals =****
>>>
>>>       vtkSmartPointer<vtkPolyDataMapper>::New();****
>>>
>>>  ****
>>>
>>>   //I chose arrows as representation****
>>>
>>>   vtkSmartPointer<vtkArrowSource> arrow =
>>> vtkSmartPointer<vtkArrowSource>::New();****
>>>
>>>   arrow->Update();****
>>>
>>>  ****
>>>
>>> //use the output of vtkPolyDataNormals as input for the glyph3d****
>>>
>>> vtkSmartPointer<vtkGlyph3D> glyph =
>>> vtkSmartPointer<vtkMaskedGlyph3D>::New();****
>>>
>>>   glyph->SetInput( normalGenerator->GetOutput() );****
>>>
>>>   glyph->SetSourceConnection(arrow->GetOutputPort());****
>>>
>>>   glyph->OrientOn();****
>>>
>>>   glyph->SetVectorModeToUseNormal();****
>>>
>>>   glyph->Update();****
>>>
>>>  ****
>>>
>>>   mapperNormals->SetInputConnection(glyph->GetOutputPort());****
>>>
>>>  ****
>>>
>>> //now follows standard code which could be taken from almost any example…
>>> ****
>>>
>>>   vtkSmartPointer<vtkActor> actorNormals =****
>>>
>>>       vtkSmartPointer<vtkActor>::New();****
>>>
>>>   actorNormals->SetMapper(mapperNormals);****
>>>
>>>  ****
>>>
>>>   // Create a renderer, render window, and interactor****
>>>
>>>   vtkSmartPointer<vtkRenderer> renderer =****
>>>
>>>       vtkSmartPointer<vtkRenderer>::New();****
>>>
>>>   vtkSmartPointer<vtkRenderWindow> renderWindow =****
>>>
>>>       vtkSmartPointer<vtkRenderWindow>::New();****
>>>
>>>   renderWindow->AddRenderer(renderer);****
>>>
>>>   vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =***
>>> *
>>>
>>>       vtkSmartPointer<vtkRenderWindowInteractor>::New();****
>>>
>>>   vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
>>> vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();****
>>>
>>>   renderWindowInteractor->SetInteractorStyle(style);****
>>>
>>>   renderWindowInteractor->SetRenderWindow(renderWindow);****
>>>
>>>  ****
>>>
>>>   // Add the actor to the scene****
>>>
>>>   renderer->AddActor(actorNormals);****
>>>
>>>  ****
>>>
>>>   // Render and interact****
>>>
>>>   renderWindow->Render();****
>>>
>>>   renderWindowInteractor->Start();****
>>>
>>>  ****
>>>
>>> Regards,****
>>>
>>> Thomas****
>>>
>>>  ****
>>>
>>>  ****
>>>
>>> Thomas Kilgus****
>>>
>>> German Cancer Research Center (DKFZ)****
>>>
>>> Div. Medical and Biological Informatics ****
>>>
>>> Junior group: Computer-assisted Interventions (E131)****
>>>
>>> Im Neuenheimer Feld 280****
>>>
>>> 69120 Heidelberg, Germany****
>>>
>>> Phone: +49(0) 6221-42-3545****
>>>
>>>  ****
>>>
>>>
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>>>
>>>  ****
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>>
>>
>>
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>> Unpaid intern in BillsBasement at noware dot com
>>
>
>
>
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