Ray tracing warning.

[claudiadom]

Hi I'm new to STIR,

Could someone explain me why is this warning showing:

WARNING: ray tracing with equal start and end point. Returning zero

Thanks beforehand.

[robbietuk]

The warning comes from here

STIR/src/recon_buildblock/RayTraceVoxelsOnCartesianGrid.cxx

Lines 51 to 67 in 8ced2d7

	void
	RayTraceVoxelsOnCartesianGrid(ProjMatrixElemsForOneBin& lor,
	const CartesianCoordinate3D<float>& start_point,
	const CartesianCoordinate3D<float>& stop_point,
	const CartesianCoordinate3D<float>& voxel_size,
	const float normalisation_constant)
	{
	const CartesianCoordinate3D<float> difference = stop_point - start_point;
	if (norm(difference) <= .00001F)
	{
	// TODO
	// not sure how to handle this case as we're normally ray tracing from voxel edges
	warning("ray tracing with equal start and end point. Returning zero");
	return;
	}

It appears to be an edge case in the ray tracer when the two coordinates are approximately the same
Could you expand on what STIR calls you are using and the parameters used to help understand the problem.