properties
- projections of parallel 3d lines intersect at a vanishing point
 - projections of parallel 3d planes intersect at a vanishing line
 - vanishing point ←> 3d direction of a line
 - vanishing line ←> 3d orientation of a surface
 
calculating points
- get edges with Canny edge detector
 - use RANSAC or Hough Transform to get lines
 - use RANSAC again in pixel space to count intersections
 
calculating lines
- calculate camera intrinsics
 - given a pair of vanishing points, …
 - a pair of vanishing points gives 1 equation
 
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related