# surface rendering artifacts

**URL:** https://discourse.vtk.org/t/surface-rendering-artifacts/8875
**Category:** Support
**Created:** [July 5, 2022, 3:52pm UTC](https://discourse.vtk.org/t/surface-rendering-artifacts/8875 "2022-07-05T15:52:18Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![Dean](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/d/3be4f8/32.png) [@Dean](https://discourse.vtk.org/u/Dean)
#### Post date: [July 5, 2022, 3:52pm UTC](https://discourse.vtk.org/t/surface-rendering-artifacts/8875/1 "2022-07-05T15:52:18Z")

</div>

I am working on transitioning legacy VTK code (5.6) to 9.1+ and am encountering rendering  
artifacts when visualizing a triangulated, mostly flat, 3D surface. The artifact does not occur with  
our legacy code but does with builds against VTK tags v9.1.0 and v9.2.0.rc1.  
A very basic pipeline with mostly defaults (ie., lighting etc.) but with customize camera parameters  
produces the artifact shown below. C++ code is provided. Any suggestions on mitigating or eliminating  
this artifact ?

A close up view of a corner of the planar surface:

 ![vtkplane_artifact_1](https://discourse.vtk.org/uploads/default/original/2X/5/55b261adbf9a00ac7890745963d4be67859e0257.jpeg)

Overview of the planar surface in wireframe:

 ![vtkplane_artifact_2](https://discourse.vtk.org/uploads/default/original/2X/6/6b3d37f0bffeb6770d26a877f2162cb8791fee11.jpeg)

Source:

```auto
// plane_artifact_vtk.cpp : A demonstration of polydata rendering artifact not present
// in vtk 5.6 (post introduction of shader support in vtk)
//

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkNew.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkPolyDataReader.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleTrackballCamera.h>

using namespace std;

int main(int argc, char* argv[])
{
	if (2 != argc)
	{
		std::cout << "Usage: plane_artifact_vtk <filename.vtp>" << std::endl;
		return EXIT_SUCCESS;
	}
	std::string filename(argv[1]);

	vtkNew<vtkRenderer> renderer;
	vtkNew<vtkCamera> camera;

	renderer->SetActiveCamera(camera);
	renderer->SetBackground(1, 1, 1);

	vtkNew<vtkRenderWindow> renderWindow;
	renderWindow->AddRenderer(renderer);
	renderWindow->SetSize(800, 800);
	renderWindow->SetWindowName("Plane Artifact VTK");

	vtkNew<vtkRenderWindowInteractor> interactor;
	interactor->SetRenderWindow(renderWindow);
	
	vtkNew<vtkInteractorStyleTrackballCamera> style;
	interactor->SetInteractorStyle(style);

	vtkNew<vtkPolyDataReader> reader;
	reader->SetFileName(filename.c_str());
	reader->Update();

	vtkNew<vtkPolyDataMapper> mapper;
	mapper->SetInputConnection(reader->GetOutputPort());

	vtkNew<vtkActor> actor;
	actor->SetMapper(mapper);
	renderer->AddViewProp(actor);

	double m_fAzimuth = 535;
	double m_fDip = 271;
	bool m_bParallelProjection = true;

	double m_fEast_Offset = -2076927.0490000001;
	double m_fNorth_Offset = -14599585.767999999;
	double m_fDepth_Offset = -6113.5580000000000;
	double m_fDistance = 40003208.092430003;
	double m_fZoomFactor = 6499379.5999999996;
	int m_nZCoordScale = 1;

	// set view up and direction of projection based on document settings
	double fAzim = m_fAzimuth / 720.0 * vtkMath::Pi();
	double fDip = m_fDip / 720.0 * vtkMath::Pi();
	double viewUp[3];

	viewUp[2] = cos(fDip);
	viewUp[0] = sin(fDip) * sin(fAzim);
	viewUp[1] = sin(fDip) * cos(fAzim);

	double focalPoint[3];
	// set focal point according to offsets 
	focalPoint[0] = -m_fEast_Offset;;
	focalPoint[1] = -m_fNorth_Offset;
	focalPoint[2] = m_fDepth_Offset * m_nZCoordScale;

	double directionOfProjection[3];
	directionOfProjection[2] = -sin(fDip);
	directionOfProjection[0] = cos(fDip) * sin(fAzim);
	directionOfProjection[1] = cos(fDip) * cos(fAzim);

	double position[3];
	position[0] = focalPoint[0] - directionOfProjection[0] * m_fDistance;
	position[1] = focalPoint[1] - directionOfProjection[1] * m_fDistance;
	position[2] = focalPoint[2] - directionOfProjection[2] * m_fDistance;

	double viewAngle = 180.0 / vtkMath::Pi() * 0.1 * 6400.0 / m_fZoomFactor;
	double m_fParallelScale = 325 * m_fDistance / m_fZoomFactor;

	std::cout << "parallel scale: " << m_fParallelScale << std::endl;
	std::cout << " distance: " << m_fDistance << std::endl;
	std::cout << " zoom factor: " << m_fZoomFactor << std::endl;
	std::cout << " east offset: " << m_fEast_Offset << std::endl;
	std::cout << " north offset: " << m_fNorth_Offset << std::endl;
	std::cout << " depth offset: " << m_fDepth_Offset << std::endl;
	std::cout << " azimuth: " << m_fAzimuth << std::endl;
	std::cout << " dip: " << m_fDip << std::endl;

	camera->SetViewUp(viewUp);
	camera->SetPosition(position);
	camera->SetFocalPoint(focalPoint);
	camera->SetViewAngle(viewAngle);
	camera->SetParallelProjection(m_bParallelProjection);
	camera->SetParallelScale(m_fParallelScale);
	camera->SetClippingRange(m_fDistance / 5, m_fDistance * 5);

	interactor->Start();

   	return EXIT_SUCCESS;
}

```

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<div class="post-metadata">

### Author: ![Dean](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/d/3be4f8/32.png) [@Dean](https://discourse.vtk.org/u/Dean)
#### Post date: [July 6, 2022, 11:54am UTC](https://discourse.vtk.org/t/surface-rendering-artifacts/8875/2 "2022-07-06T11:54:37Z")

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I discovered by inserting vtkPolyDataNormals between reader and mapper the artifact is eliminated.  
Another solution is to force the renderer to call ResetCamera() (eg., ‘r’ or 'R" key press) which  
adjusts/resets the camera clipping range and parallel scale based on visible prop bounds. If  
anyone has some insight as to why the artifact occurs post vtk 5.6 please comment.

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### Author: ![marcomusy](https://discourse.vtk.org/user_avatar/discourse.vtk.org/marcomusy/32/95_2.png) [@marcomusy](https://discourse.vtk.org/u/marcomusy)
#### Post date: [July 6, 2022, 4:24pm UTC](https://discourse.vtk.org/t/surface-rendering-artifacts/8875/3 "2022-07-06T16:24:43Z")

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have you tried with `.GetProperty().SetInterpolationToFlat()`

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<div class="post-metadata">

### Author: ![Dean](https://discourse.vtk.org/letter_avatar_proxy/v4/letter/d/3be4f8/32.png) [@Dean](https://discourse.vtk.org/u/Dean)
#### Post date: [July 6, 2022, 5:32pm UTC](https://discourse.vtk.org/t/surface-rendering-artifacts/8875/4 "2022-07-06T17:32:04Z")

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Hi Marco,

if I set the actor interpolation to flat, then my fix with poly data normals  
no longer works … so does not resolve the issue. So far, the only fix that works directly  
is polydata normals and indirectly regardless of interpolation mode is forcing reset camera clipping range.