# Outline/silhouette a subset of points

**URL:** https://discourse.vtk.org/t/outline-silhouette-a-subset-of-points/8470
**Category:** Support
**Created:** [May 11, 2022, 7:56am UTC](https://discourse.vtk.org/t/outline-silhouette-a-subset-of-points/8470 "2022-05-11T07:56:01Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![CharInt0](https://discourse.vtk.org/user_avatar/discourse.vtk.org/charint0/32/2983_2.png) [@CharInt0](https://discourse.vtk.org/u/CharInt0)
#### Post date: [May 11, 2022, 7:56am UTC](https://discourse.vtk.org/t/outline-silhouette-a-subset-of-points/8470/1 "2022-05-11T07:56:01Z")

</div>

Hello,  
I am trying to add an outline (or better a silhouette) to a subset of points visualized as a Glyph3D. I already managed to change the color to the subset points. In my code, I use vtkExtractGeometry and vtkVertexGlyphFilter to extract the subset from the point set. This work as expected and I obtain the subset point’s ID that I use to change the points’ colors:

```auto
auto* frustum = static_cast<vtkAreaPicker*>(GetInteractor()->GetPicker())->GetFrustum();
vtkNew<vtkExtractGeometry> extractGeometry;
extractGeometry->SetImplicitFunction(frustum);
extractGeometry->SetInputData(ptsElement->getGlyph()->GetOutput());
extractGeometry->Update();

vtkNew<vtkVertexGlyphFilter> glyphFilter;
glyphFilter->SetInputConnection(extractGeometry->GetOutputPort());
glyphFilter->Update();

auto* selected = glyphFilter->GetOutput();

```

For the outline I use a vtkOutlineSource with a vtkPolyDataMapper to create a vtkGlyph3D for the subset:

```auto
Outline = vtkSmartPointer<vtkOutlineSource>::New();

OutlineGlyph = vtkSmartPointer<vtkGlyph3D>::New();
OutlineGlyph->ScalingOff();
OutlineGlyph->SetScaleModeToDataScalingOff();
OutlineGlyph->SetSourceConnection(Outline->GetOutputPort());
OutlineMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
OutlineMapper->SetInputConnection(OutlineGlyph->GetOutputPort());
OutlineActor = vtkSmartPointer<vtkActor>::New();
OutlineActor->SetMapper(OutlineMapper);
OutlineActor->GetProperty()->SetColor(1.0, 0.0, 0.0);
OutlineActor->GetProperty()->SetAmbient(1.0);
OutlineActor->GetProperty()->SetDiffuse(0.0);

```

Then I pass the above glyphFilter output to the OutlineGlyph:

```auto
OutlineGlyph->SetInputData(selected);
//glyph3D->SetScaleFactor(scaleFactor);
OutlineGlyph->Update();

GetDefaultRenderer()->AddActor(OutlineActor);

```

What I obtain is that the selected points (in green) have some scattered red dots added but not and outline:  
 ![image](https://discourse.vtk.org/uploads/default/original/2X/2/2c565a5c15bc7374658c56ed92861832f9b2dce6.png)

I tried also drawing a Silhouette with vtkPolyDataSilhouette but it worked only when drawing on the whole point set but nothing showed up when passing the subset data.  
An alternative approach, yet much less efficient I think, could be to create an actor for each subset’s point.  
Any help is much appreciated,  
Carlo

---

<div class="post-metadata">

### Author: ![CharInt0](https://discourse.vtk.org/user_avatar/discourse.vtk.org/charint0/32/2983_2.png) [@CharInt0](https://discourse.vtk.org/u/CharInt0)
#### Post date: [May 12, 2022, 6:42am UTC](https://discourse.vtk.org/t/outline-silhouette-a-subset-of-points/8470/2 "2022-05-12T06:42:54Z")

</div>

I think that I figured it out:  
 ![image](https://discourse.vtk.org/uploads/default/original/2X/7/74fef0bcdd0aafb8325afbe152a9f178a5907cc0.png)

I create a new Polydata and I obtain the coordinates of the points. This last part is not completely correct as I am not taking the glyph centers because the selected-\>GetPoints(); returns many more points than the point coordinates but I am trying to fix this now.  
Sketchy code:

```auto
auto* selected = glyphFilter->GetOutput();
auto* ids = dynamic_cast<vtkIdTypeArray*>(selected->GetPointData()->GetArray("InputPointIds"));

auto* selPoints = selected->GetPoints();
vtkNew<vtkPoints> selPointsData;

auto* ptsData = static_cast<vtkPolyData*>(data.GetPointer());

auto* colors = vtkUnsignedCharArray::SafeDownCast(ptsData->GetPointData()->GetScalars(colorsName.c_str()));

long long uniquePtId = -1;
for (auto i = 0; i < ids->GetNumberOfValues(); i++)
{
  auto ptId = ids->GetValue(i);
  if (uniquePtId == ptId)
  {
    continue;
  }
 
  double pt[3];
  selPoints->GetPoint(i, pt);
  std::cout << "x: " << pt[0] << " y: " << pt[1] << " z: " << pt[2] << std::endl;
  
  selPointsData->InsertNextPoint(pt);
  uniquePtId = ptId;
}

vtkNew<vtkPolyData> polydata;
polydata->SetPoints(selPointsData);

OutlineGlyph->SetInputData(polydata);
OutlineGlyph->SetScaleFactor(600.0);
OutlineGlyph->Update();

GetDefaultRenderer()->AddActor(OutlineActor);

```