Semi-automated Generation of Geometric Digital Twin for Bridge Based on Terrestrial Laser Scanning Data

Algorithm 1

Improved RANSAC algorithm.

	Input: cross-sectional pier column with two-side point clouds list Datan×3;
	Output: The improved RANSAC algorithm’s Distance threshold , the axis of the pier column .
	Dataz = Datan × 3 (:, 3);
	dz = 1000; //Cut the interval of Data along the Z-axis in a plane parallel.
	kz;//Quotient of total length of Dataz and dz.
	dx = 1; //millimeter.
	kx;//Number of millimeters along the X-axis of each cross section.
	for i = 1to kz do
	Datai; //Obtain the Point clouds of each segment of point clouds after cutting.
	, ;// is the total number of points on the X-axis a of the cross section. a is the width of the cross section.
	; //The average density is calculated ρ Along the X axis.
	; //Definition the density threshold.
	for j = 1to kx do
	; //Calculated the number of point clouds per millimeter along X-axis.
	end for
	Tx; //Find the number greater than in , and then the product of dx.
	Ty; //It is the same as the solution process Tx.
	l1 = RANSAC (Data, Tx); //Using RANSAC algorithm to fit straight line.
	Data0; //Delete the point cloud in Data used in l1
	l2 = RANSAC (Data0, Ty); //Using RANSAC algorithm to fit remaining straight line.
	l3 = l1 + (0, 0, a); //the translation strategy is used to supplement the unknown line segment.
	l4 = l2 + (0, 0, b); //like l3.
	[Pt1, Pt2, Pt3, Pt4]; //calculate the intersection of l1, l2, l3, l4.
	Pc; //calculate the centroid of the intersection.
	end for
	; //calculate the axis of the pier column.