Novel method for sphere target detection and center estimation from mobile terrestrial laser scanner data

An Automatic Spherical Targets Detection Method with Multiple Geometrical Constraints

“…For the background of spherical target in radial direction is missing, the improved three points filter method is proposed to detect possible spherical points. In this method, its radial distance is set as a fixed value to meet the requirement of the three points filter method [7] if the neighborhood point is missing. This ensures that the spherical targets without the background in radial direction can be detected.…”

“…When the background of spherical targets in radial direction is missing (Figure 1 (a)), partial or all three neighborhood points , i j t P , , i j t P and , i t j P of , i j P will be missing (Figure 1(b)). In this case the three points filter method [7] is unable to get the all three radial distances , i j t r , , i j t r and , i t j r , therefore, the spherical target will not be detected. To solve this problem, the radial distance is set to , 2 i j r if any of three neighborhood points is missing.…”

“…The potential target point clouds , 1, 2... Sphere can be extracted by the RANSAC method [3,6,7], which is less affected by noise. However, in some case, some false spherical targets are detected by the RANSAC method.…”

“…As to the proposed method, th R is set to 0.01m and th Ratio is set to 0.6. As to the three points filter method [7], the inner radius min R is set to 1.5R and the outer radius max R is set to 2R in this paper.…”

“…Wang et al [6] extracts the occluding edge points according to the depth difference between the center point p and the local eight neighborhoods, then the spherical targets are detected by the RANSAC method. Liu et al [7] used the three points filter method to extract possible spherical points, and detected the spherical targets. The method assuming that the background of spherical targets in radial direction is always existing.…”