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@decrispell
Last active March 1, 2024 02:47
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Convert standard camera intrinsic (focal length, principal point) and extrinsic parameters (rotation and translation) into a vtkCamera for rendering. Assume square pixels and 0 skew for now.
/**
* Convert standard camera intrinsic and extrinsic parameters to a vtkCamera instance for rendering
* Assume square pixels and 0 skew (for now).
*
* focal_len : camera focal length (units pixels)
* nx,ny : image dimensions in pixels
* principal_pt: camera principal point,
* i.e. the intersection of the principal ray with the image plane (units pixels)
* camera_rot, camera_trans : rotation, translation matrix mapping world points to camera coordinates
* depth_min, depth_max : needed to set the clipping range
*
**/
vtkSmartPointer<vtkCamera> make_vtk_camera(double focal_len,
int nx, int ny,
vgl_point_2d<double> const& principal_pt,
vgl_rotation_3d<double> const& camera_rot,
vgl_vector_3d<double> const& camera_trans,
double depth_min, double depth_max)
{
// create the camera
vtkSmartPointer<vtkCamera> camera = vtkSmartPointer<vtkCamera>::New();
// convert camera rotation and translation into a 4x4 homogeneous transformation matrix
vtkSmartPointer<vtkMatrix4x4> camera_RT = make_transform(camera_rot, camera_trans);
// apply the transform to scene objects
camera->SetModelTransformMatrix( camera_RT );
// the camera can stay at the origin because we are transforming the scene objects
camera->SetPosition(0, 0, 0);
// look in the +Z direction of the camera coordinate system
camera->SetFocalPoint(0, 0, 1);
// the camera Y axis points down
camera->SetViewUp(0,-1,0);
// ensure the relevant range of depths are rendered
camera->SetClippingRange(depth_min, depth_max);
// convert the principal point to window center (normalized coordinate system) and set it
double wcx = -2*(principal_pt.x() - double(nx)/2) / nx;
double wcy = 2*(principal_pt.y() - double(ny)/2) / ny;
camera->SetWindowCenter(wcx, wcy);
// convert the focal length to view angle and set it
double view_angle = vnl_math::deg_per_rad * (2.0 * std::atan2( ny/2.0, focal_len ));
std::cout << "view_angle = " << view_angle << std::endl;
camera->SetViewAngle( view_angle );
return camera;
}
/**
* Helper function: Convert rotation and translation into a vtk 4x4 homogeneous transform
*/
vtkSmartPointer<vtkMatrix4x4> make_transform(vgl_rotation_3d<double> const& R,
vgl_vector_3d<double> const& T)
{
vtkSmartPointer<vtkMatrix4x4> m = vtkSmartPointer<vtkMatrix4x4>::New();
vnl_matrix_fixed<double,3,3> R_mat = R.as_matrix();
for (int r=0; r<3; ++r) {
for (int c=0; c<3; ++c) {
m->SetElement(r,c,R_mat[r][c]);
}
}
m->SetElement(0,3,T.x());
m->SetElement(1,3,T.y());
m->SetElement(2,3,T.z());
m->SetElement(3,3,1);
return m;
}
@decrispell
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I believe there is no negative sign on wcy because the direction of the y axis is "up" in the opengl normalized coordinate system. That said, this code may have only been tested with the principal point at the image center, in which case the term in the parentheses is 0 and the negative sign (or lack thereof) doesn't matter. So it is possible that something is wrong - (Sorry, it's been a while)

If you are increasing the window size (nx and ny), you probably also want to increase the principal point, so keep that in mind.

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