Planar coding target for vision system and real-time pose measurement method thereof

A real-time pose measurement method of a planar coding target, wherein the real-time pose measurement method is applied to a vision system comprising the planar coding target, an image acquisition device and a data processing device;

• the image acquisition device is configured to capture an image of the planar coding target and send the image of the planar coding target to the data processing device for processing;
• the planar coding target comprises a coding template, and a coding pattern;
• the coding template comprises at least one coding bock;
• each of the at least one coding block comprises four coding elements;
• a pattern of the coding template is a minimum identification unit pattern;
• each of the four coding elements has a unique coding value;
• and coding values of the four coding elements are different from each other;
• the four coding elements are distributed in a rectangle ABCD and do not overlap with each other;
• a center of each of the at least one coding block is an intersection point O of two diagonals of the rectangle ABCD;
• each of the at least one coding block has a coding value;
• wherein the coding value of the at least one coding block is associated with a coding value of each of the four coding elements contained in the at least one coding block;
• each of the at least one coding block is a special coding block or a conventional coding block;
• in the special coding block, gravity centers of three of the four coding elements are respectively located at vertexes B, C, D of the rectangle ABCD, and a gravity center of the remaining one of the four coding elements is located in a triangle enclosed by the vertexes A, B and C, and is defined as point E;
• in the conventional coding block, gravity centers of the four coding elements are respectively located at vertexes A, B, C and D of the rectangle ABCD;
• the at least one coding block has determined mutual position and arrangement relationship;
• the at least one coding block comprises at least one special coding block;
• the coding template is configured to mark the at least one coding block each with an integer serial number according to a preset order, so as to generate a coding value of the at least one coding block;
• according to the sequence of the at least one coding block on the coding template, coding values of the at least one coding block are obtained in turn to form a coding value sequence [V0, V1, . . . , VK-1] of the minimum identification unit pattern;
• wherein V0, V1, . . . , Vk-1 are coding values of the at least one coding block;
• and K is the number of the at least one coding block in the coding template;
• the coding value sequence of the minimum identification unit pattern is unique, and coding value sequences of different minimum identification unit patterns are different from each other;
• the coding pattern is generated through continuous movement and expansion of the coding template;
• the coding pattern covers a surface of a target board;
• the coding pattern is provided with a corresponding coding information matrix;
• and the coding information matrix is configured to store type and coding value of each coding block contained in the coding pattern;
• and
• the real-time pose measurement method comprises:
• (1) generating, by the data processing device, a coding pattern according to requirements of a measurement scene and arranging the coding pattern on the surface of the target board, so as to form the planar coding target;
• (2) establishing, by the data processing device, a coordinate system O-UV of the image of the planar coding target, a coordinate system Oc-XcYcZc of the image acquisition device and a coordinate system Ow-XwYwZw of the planar coding target;
• (3) solving a rotation matrix R and a translation matrix T by using a perspective-n-point (PnP) algorithm, wherein the rotation matrix R is configured to transform coordinates of a point from the coordinate system Ow-XwYwZw to the coordinate system Oc-XcYcZc, and the translation matrix T is configured to transform coordinates of a point from the coordinate system Ow-XwYwZw to the coordinate system Oc-XcYcZc;
• (4) acquiring a coordinate transformation relationship of an object to be measured between the coordinate system Oc-XcYcZc and the coordinate system Ow-XwYwZw, expressed as Pc=R·Pw+T;
• wherein Pc represents a coordinate of the object to be measured in the coordinate system Oc-XcYcZc;
• and Pw represents a coordinate of the object to be measured in the coordinate system Ow-XwYwZw;
• and
• (5) continuously shooting, by the image acquisition device, a local coding pattern of the planar coding target during movement of the object to be measured;
• and calculating, by the data processing device, a pose change of the object to be measured in real time in the coordinate system Ow-XwYwZw relative to the coordinate system Oc-XcYcZc.