CODEWITHSUNDEEP
computer-visionpointpoint-cloudsransac
Satwik Priyadarshi
Satwik Priyadarshi

Reputation: 45

RANSAC Settings: A few questions on parameters, primitives, and iterations

RANSAC Settings: A few questions on parameters, primitives, and iterations-

  1. While segmenting a 3D point cloud,how the minimum number of support points per primitive is decided in RANSAC?

  2. Furthermore, out of 5 primitives : Plane, Sphere, Cone, Cylinder, Torus which primitives should be selected and how?

  3. How maximum number of iterations in decided in RANSAC?

Reference: Schnabel, Ruwen, Roland Wahl, and Reinhard Klein. "Efficient RANSAC for Point‐Cloud Shape Detection." Computer graphics forum. Vol. 26. No. 2. Blackwell Publishing Ltd, 2007.

Upvotes: 1

Views: 1689

Answers (1)

user3146587
user3146587

Reputation: 4320

  1. The minimum number of support points per primitive depends on the kind of primitive itself: it is the minimum number of points required to fit a primitive and recover its parameters. In some cases this minimum number of points also depends the actual method used to recover the parameters of an instantiated primitive from support points.

    For instance:

    • Plane: 3 points are sufficient,

    • Sphere: 4 points are sufficient,

    • Cylinder: 3 points would work (find the plane of the points and fit a circle, the axis of the cylinder is the normal of the plane going through the center of the circle),

    • Cone: 4 points would work (find the plane of the first three points and fit a circle like before, find the slope of the cone by using the 4th point).

  2. This would depend on what is expected to be found in the input point cloud: if there is no cone or torus, it would make sense to not try fitting cones or tori. Starting with planes only and then extending to sphere and cylinders would already be a good start.

  3. The number of iterations is based on the desired confidence and an estimate or guess of the ratio of inliers (See: http://en.wikipedia.org/wiki/RANSAC#Parameters for the standard formula).

Upvotes: 2

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