Render RGB-D image from mesh - c++

Question

I have a mesh model (.ply file) and I have rendered it with VTK and changed the camera viewpoint.
From the new camera viewpoint how can I render an RGB and a depth image? I think this might be raytracing, but not sure
EDIT
I want to generate a real depth map, as opposed to just a visualization of the depth. The visualization can be achieved by using values in Z buffer and scaling between 0-255 but this does not provide real depth information.

Answer 1

To get the real world depth from the camera I have done the following:
double z = render_win->GetZbufferDataAtPoint(x,y);
worldPicker->Pick(x, y, z, renderer);
worldPicker->GetPickPosition(coords);
double euclidean_distance = sqrt(pow((coords[0] - cam_pos[0]), 2) + pow(coords[1] - cam_pos[1], 2) + pow(coords[2] - cam_pos[2], 2));
where cam_pos is the camera position in real world coordinates. This seems to do the trick

Answer 2

Here is a short few lines if you already have the application set up and rendering, this has to be after the mesh has rendered at least once
// Screenshot
vtkSmartPointer<vtkWindowToImageFilter> windowToImageFilter =
vtkSmartPointer<vtkWindowToImageFilter>::New();
windowToImageFilter->SetInput(renderWindow);
windowToImageFilter->SetMagnification(3); //set the resolution of the output image (3 times the current resolution of vtk render window)
windowToImageFilter->SetInputBufferTypeToRGBA(); //also record the alpha (transparency) channel
windowToImageFilter->Update();
vtkSmartPointer<vtkPNGWriter> writer =
vtkSmartPointer<vtkPNGWriter>::New();
writer->SetFileName("screenshot2.png");
writer->SetInputConnection(windowToImageFilter->GetOutputPort());
writer->Write();
This is from the VTK Public Wiki

Answer 3

To retrieve RGB image you can use vtkWindowToImageFilter class, allowing to read data from the vtkWindow.
For the Depth Image, i tried a solution which is to modify color on the mesh using vtkDepthSortPolyData , and again, read from the window.
See the example above :
# define VTK_CREATE(type, nom) vtkSmartPointer<type> nom = vtkSmartPointer<type>::New()
int main ()
{
VTK_CREATE(vtkPLYReader, reader);
reader->SetFileName ("mesh.ply");
reader->Update ();
// create depth sort algo
VTK_CREATE(vtkDepthSortPolyData, sort);
sort->SetInput(reader->GetOutput ());
// init stuff for rendering
VTK_CREATE(vtkPolyDataMapper, mapper);
VTK_CREATE(vtkActor, actor);
VTK_CREATE(vtkRenderer, rend);
VTK_CREATE(vtkRenderWindow, rw);
VTK_CREATE(vtkRenderWindowInteractor, inte);
VTK_CREATE(vtkCamera, cam);
sort->SetDirectionToBackToFront (); // camera direction
sort->SetCamera (cam); // set camera or runtime warning
sort->SortScalarsOn ();
sort->Update ();
mapper->SetScalarVisibility(true);
// limit max scalar (nb Color)
mapper->SetScalarRange (0, sort->GetOutput ()->GetNumberOfCells ());
mapper->SetInputConnection(sort->GetOutputPort ());
mapper->Update ();
actor->SetMapper(mapper);
actor->RotateY (59); // transform with a rotation to see depth
actor->GetProperty()->SetColor(1, 0, 0);
sort->SetProp3D (actor); // set the actor to the algo
rend->SetActiveCamera (cam);
rw->AddRenderer(rend);
rend->AddActor(actor);
inte->SetRenderWindow (rw);
inte->Initialize ();
// read depth image from vtk Window
VTK_CREATE (vtkWindowToImageFilter, screen);
screen->SetInput (rw);
screen->Update ();
// start rendering for visualization
rw->Render ();
// save the depth img as a png
VTK_CREATE(vtkPNGWriter, writer);
writer->SetFileName ("output.png");
writer->SetInputConnection (screen->GetOutputPort ());
writer->Write ();
inte->Start ();
return 0;
}
Tested on VTK 5.10.