[vtkusers] Question about surface normal

[Luca Pamparana]

Hello everyone,

Started playing with vtk recently and have a simple code that simply
draws a 2D plane in 3D space. I am using vtkPolyData class and using a
vtkActor to render it.

This might be more of a geometry question. So, what I want to do is
have the surface normal point to a given point in 3D space. For
example, I might want the normal to point to the origin of my 3D
scene. Does anyone know how I might be able to calculate that.

Here is the bit of code that I have so far, which I have hacked
together after looking at some VTK examples.


// Code starts
#include "vtkPoints.h"
#include "vtkCellArray.h"
#include "vtkPolyData.h"
#include "vtkPolyDataMapper.h"
#include "vtkActor.h"
#include "vtkRenderWindow.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkRenderer.h"
#include "vtkProperty.h"


int main()
{
    vtkPolyData * geometry = vtkPolyData::New();
    vtkPoints * testPoints = vtkPoints::New();
    testPoints->Allocate(4);
    vtkCellArray *testPolys = vtkCellArray::New();
    testPolys->Allocate(testPolys->EstimateSize(1,4));
    double x[3];
    vtkIdType pts[4];
    x[0] = -2.5;
    x[1] = -2.5;
    x[2] = -2.5;
    testPoints->InsertNextPoint(x);
    x[0] = 2.5;
    x[1] = -2.5;
    x[2] = -2.5;
    testPoints->InsertNextPoint(x);
    x[0] = -2.5;
    x[1] = 2.5;
    x[2] = -2.5;
    testPoints->InsertNextPoint(x);
    x[0] = 2.5;
    x[1] = 2.5;
    x[2] = -2.5;
    testPoints->InsertNextPoint(x);

    pts[0] = 0; pts[1] = 2; pts[2] = 3; pts[3] = 1;
    testPolys->InsertNextCell(4,pts);
    geometry->SetPoints(testPoints);
    testPoints->Delete();
    testPolys->Squeeze();
    geometry->SetPolys(testPolys);
    testPolys->Delete();

    vtkRenderer *renderer = vtkRenderer::New();
    vtkRenderWindow *renWin = vtkRenderWindow::New();
    renWin->AddRenderer(renderer);
    vtkRenderWindowInteractor *iren = vtkRenderWindowInteractor::New();
    iren->SetRenderWindow(renWin);

    vtkPolyDataMapper * testMapper = vtkPolyDataMapper::New();
    testMapper->SetInput(geometry);

    vtkActor * testActor = vtkActor::New();
    testActor->SetMapper(testMapper);
    testActor->GetProperty()->SetColor(1, 0, 0);
    renderer->AddActor(testActor);
    renderer->SetBackground(1,1,1);
    renWin->SetSize(300,300);

    renWin->Render();

    iren->Start();

    testActor->Delete();
    testMapper->Delete();
    iren->Delete();
    renWin->Delete();
    renderer->Delete();
    return 0;
}
// Code ends

Looking forward to your help.

Sincerely,

Luc