	US 12,272,074 B1
	Method and system for converting trajectory coordinates of moving objects
Xu Wang, Jinan (CN); Fei Ma, Jinan (CN); Rongjian Dai, Jinan (CN); and Tong Zhou, Jinan (CN)
Assigned to SHANDONG UNIVERSITY, Jinan (CN)
Filed by SHANDONG UNIVERSITY, Jinan (CN)
Filed on Nov. 7, 2024, as Appl. No. 18/939,635.
Claims priority of application No. 202410873721.7 (CN), filed on Jul. 2, 2024.
Int. Cl. G06K 9/00 (2022.01); G06T 7/20 (2017.01); G06T 7/70 (2017.01)

CPC G06T 7/20 (2013.01) [G06T 7/70 (2017.01); G06T 2207/10016 (2013.01); G06T 2207/10032 (2013.01); G06T 2207/20084 (2013.01); G06T 2207/30241 (2013.01)]

8 Claims

1. A method for converting trajectory coordinates of moving objects, comprising:

obtaining a video of a moving object captured by a drone, and extracting trajectory data of the moving object in a pixel coordinate system from the captured video; wherein, extracting and analyzing the trajectory data by using a two-stage object detection and tracking algorithm;

for any target point in the trajectory data of the moving object, based on location information of the drone, attitude information of the camera, and intrinsic parameter information of the camera during capturing of each frame of the video, in combination with pixel coordinates of the target point in the pixel coordinate system, solving a representation of a unit direction vector corresponding to the target point in a camera coordinate system in an ECEF coordinate system, to obtain a representation of a vector from an ECEF origin to the target point, wherein a unit direction vector corresponding to a point A in the camera coordinate system is expressed as v_ecef in the ECEF coordinate system, and is specifically as follows:

v_ecef=T·R_NED^ENU·R·v_n=(x_v,y_v,z_v), wherein

R=R_z·R_y·R_x,

and

where, R is a rotation matrix from the camera coordinate system to a north-east-down coordinate system with the camera as an origin, R_NED^ENUis a rotation matrix from the north-east-down coordinate system to an east-north-up coordinate system, T is a rotation matrix from the east-north-up coordinate system to the ECEF coordinate system, and v is the unit direction vector corresponding to the target point in the camera coordinate system;

R_z, R_y, and R_x are transformation matrices in a case in which the coordinate system rotates around a Z-axis, a Y-axis, and an X-axis respectively; and, lon and lat indicate a longitude and a latitude in location information of a drone respectively;

a vector from an ECEF origin to the camera is expressed in the ECEF coordinate system by using longitude, latitude, and altitude as follows:

c_ecef=transform_wgs84^ECEF(lon,lat,alt)=(x_c,y_c,z_c),

where, transform_wgs84^ECEFindicates conversion from coordinates in a WGS84 coordinate system to corresponding coordinates in the ECEF coordinate system, and (x_c,y_c,z_c) is a representation of the vector from the ECEF origin to the camera in the ECEF coordinate system; and, alt indicates an altitude in the location information of the drone; and

a vector from the ECEF origin to the point A is expressed as follows:

a_ecef=c_ecef+kv_ecef=(x_c+kx_v,y_c+ky_v,z_c+kz_v),

where, k indicates modulus of a vector from an origin of the camera coordinate system to the target point A; and

representing coordinates of the target point in the WGS84 coordinate system by using the representation of the vector from the ECEF origin to the target point, and finally obtaining, through solving, the coordinates of the target point in the WGS84 coordinate system based on that an altitude of the target point is the same as an altitude at which the drone takes off.