Patent ID: 11900634
Assignee: DALIAN UNIVERSITY OF TECHNOLOGY
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G  H | IPC G  H

Claim 3:
4. The method for adaptively detecting chessboard sub-pixel level corner points according to claim 1, wherein step 5) comprises the following specific steps:
5-1) using the coordinates P1, P2, P3 and P4 of the four initial corner points of the initially marked unit grid; according to the imaging principle of the camera, the pixel coordinate of a projection point P in the pixel coordinate system of a point W(Xw, Yw, Zw) in the world coordinate system is (u, v), i.e.:, Z
    c
   
   [
   
    
     
      u
     
    
    
     
      v
     
    
    
     
      1
     
    
   
   ]
  
  =
  
   
    
     
      
       [
       
        
         
          
           1
           
            d
            ⁢
            x
           
          
         
         
          0
         
         
          
           u
           0
          
         
        
        
         
          0
         
         
          
           1
           
            d
            ⁢
            y
           
          
         
         
          
           v
           0
          
         
        
        
         
          0
         
         
          0
         
         
          1
         
        
       
       ]
      
      [
      
       
        
         f
        
        
         0
        
        
         0
        
        
         0
        
       
       
        
         0
        
        
         f
        
        
         0
        
        
         0
        
       
       
        
         0
        
        
         0
        
        
         1
        
        
         0
        
       
      
      ]
     
     [
     
      
       
        R
       
       
        T
       
      
      
       
        
         0
         →
        
       
       
        1
       
      
     
     ]
    
    [
    
     
      
       
        X
        w
       
      
     
     
      
       
        Y
        w
       
      
     
     
      
       
        Z
        w
       
      
     
     
      
       1
      
     
    
    ]
   
   =
   
    
    
     
      
       [
       
        
         
          
           f
           x
          
         
         
          0
         
         
          
           u
           0
          
         
         
          0
         
        
        
         
          0
         
         
          
           f
           y
          
         
         
          
           v
           0
          
         
         
          0
         
        
        
         
          0
         
         
          0
         
         
          1
         
         
          0
         
        
       
       ]
      
      [
      
       
        
         R
        
        
         T
        
       
       
        
         
          0
          →
         
        
        
         1
        
       
      
      ]
     
     [
     
      
       
        
         X
         w
        
       
      
      
       
        
         Y
         w
        
       
      
      
       
        
         Z
         w
        
       
      
      
       
        1
       
      
     
     ]
    
   
  
 

wherein Zc is the Z-coordinate of point W in a camera coordinate system, u0 is the center coordinate of the image in x direction, v0, is the center coordinate of the image in y direction, f is a focal length, R is a rotation matrix, T is a translation vector, fx is a scale factor on u axis, fy is a scale factor on v axis, dx is a pixel size in x direction, and dy is a pixel size in y direction;
5-2) recording Z=0 of a point in the plane of the chessboard calibration target, so:, Z
    c
   
   [
   
    
     
      u
     
    
    
     
      v
     
    
    
     
      1
     
    
   
   ]
  
  =
  
   
    
     
      
       [
       
        
         
          
           1
           
            d
            ⁢
            x
           
          
         
         
          0
         
         
          
           u
           0
          
         
        
        
         
          0
         
         
          
           1
           
            d
            ⁢
            y
           
          
         
         
          
           v
           0
          
         
        
        
         
          0
         
         
          0
         
         
          1
         
        
       
       ]
      
      [
      
       
        
         f
        
        
         0
        
        
         0
        
        
         0
        
       
       
        
         0
        
        
         f
        
        
         0
        
        
         0
        
       
       
        
         0
        
        
         0
        
        
         1
        
        
         0
        
       
      
      ]
     
     [
     
      
       
        
         r
         1
        
       
       
        
         r
         2
        
       
       
        
         r
         3
        
       
       
        t
       
      
     
     ]
    
    [
    
     
      
       
        X
        w
       
      
     
     
      
       
        Y
        w
       
      
     
     
      
       0
      
     
     
      
       1
      
     
    
    ]
   
   =
   
    
    
     
      
       [
       
        
         
          
           f
           x
          
         
         
          0
         
         
          
           u
           0
          
         
         
          0
         
        
        
         
          0
         
         
          
           f
           y
          
         
         
          
           v
           0
          
         
         
          0
         
        
        
         
          0
         
         
          0
         
         
          1
         
         
          0
         
        
       
       ]
      
      [
      
       
        
         
          r
          1
         
        
        
         
          r
          2
         
        
        
         t
        
       
      
      ]
     
     [
     
      
       
        
         X
         w
        
       
      
      
       
        
         Y
         w
        
       
      
      
       
        1
       
      
     
     ]
    
   
  
 

wherein r1, r2 and r3 are three column vectors of the rotation matrix R respectively, and t is a translation vector in x and y directions;
based on that ZcP′=HW′, letting, A
   =
   
    [
    
     
      
       
        f
        x
       
      
      
       0
      
      
       
        u
        0
       
      
      
       0
      
     
     
      
       0
      
      
       
        f
        y
       
      
      
       
        v
        0
       
      
      
       0
      
     
     
      
       0
      
      
       0
      
      
       1
      
      
       0
      
     
    
    ]
   
  
  ,, then the homography matrix H is obtained:

H=A[r1r2].