How to select all the elements of a point cloud that are aligned at +-45 degrees?

Hi, I have a point cloud in x,y,z coordinates its shape is rectangular, and I want to select all the elements that are near a line that could be oriented at 45 degrees. None of the points are exactly at the position of a line if I draw it, so I need to specify a range of distances between the points and that imaginary line at 45 degrees.

Thank you in advance! Martha