Why does the vtkOBJReader add point automatically?

Support
1

Hello,I have an cube in obj format with content like this:

o Cube
v 1.000000 1.000000 -1.000000
v 1.000000 -1.000000 -1.000000
v 1.000000 1.000000 1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 1.000000 -1.000000
v -1.000000 -1.000000 -1.000000
v -1.000000 1.000000 1.000000
v -1.000000 -1.000000 1.000000
vn 0.0000 1.0000 0.0000
vn 0.0000 0.0000 1.0000
vn -1.0000 0.0000 0.0000
vn 0.0000 -1.0000 0.0000
vn 0.0000 0.0000 -1.0000
s off
f 1//1 5//1 7//1 3//1
f 4//2 3//2 7//2 8//2
f 8//3 7//3 5//3 6//3
f 6//4 2//4 4//4 8//4
f 2//3 4//3 3//3 1//3
f 6//5 5//5 1//5 2//5

Below code:

#include <vtkOBJReader.h>
#include <vtkNew.h>
#include <vtkCleanPolyData.h>

int main(int, char*[]) {

	auto fileName = "/path/to/above/objFile.obj";

	vtkNew<vtkOBJReader> reader;
	reader->SetFileName(fileName);
	reader->Update();
	auto rawPD = reader->GetOutput();

	std::cout << "Point number before clean: " << rawPD->GetNumberOfPoints() << std::endl << std::endl;

	vtkNew<vtkCleanPolyData> clean;
	clean->SetInputData(rawPD);
	clean->SetTolerance(0.0);
	clean->PointMergingOn();
	clean->Update();

	auto pd=clean->GetOutput();

	std::cout << "Point number after clean: " << pd->GetNumberOfPoints() << std::endl << std::endl;
}

Outputs:

Point number before clean: 24

Point number after clean: 8

Why?

2

Faces 0 and 1 share point 3, but that point has different normals in the two faces (0 and 1). That point is duplicated.
Same happens for other shared points that have different normals. This is also important (more important) for texture coordinates.

3

Thanks,aren’t these normals for point but for face itself?

4

They are specified for every point of the face isn’t it?