| 1 | %init_intrinsic_param |
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| 2 | % |
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| 3 | %Initialization of the intrinsic parameters. |
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| 4 | %Runs as a script. |
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| 5 | % |
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| 6 | %INPUT: x_1,x_2,x_3,...: Feature locations on the images |
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| 7 | % X_1,X_2,X_3,...: Corresponding grid coordinates |
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| 8 | % |
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| 9 | %OUTPUT: fc: Camera focal length |
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| 10 | % cc: Principal point coordinates |
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| 11 | % kc: Distortion coefficients |
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| 12 | % alpha_c: skew coefficient |
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| 13 | % KK: The camera matrix (containing fc, cc and alpha_c) |
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| 14 | % |
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| 15 | %Method: Computes the planar homographies H_1, H_2, H_3, ... and computes |
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| 16 | % the focal length fc from orthogonal vanishing points constraint. |
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| 17 | % The principal point cc is assumed at the center of the image. |
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| 18 | % Assumes no image distortion (kc = [0;0;0;0]) |
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| 19 | % |
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| 20 | %Note: The row vector active_images consists of zeros and ones. To deactivate an image, set the |
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| 21 | % corresponding entry in the active_images vector to zero. |
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| 22 | % |
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| 23 | % |
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| 24 | %Important function called within that program: |
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| 25 | % |
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| 26 | %compute_homography.m: Computes the planar homography between points on the grid in 3D, and the image plane. |
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| 27 | % |
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| 28 | % |
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| 29 | %VERY IMPORTANT: This function works only with 2D rigs. |
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| 30 | %In the future, a more general function will be there (working with 3D rigs as well). |
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| 31 | |
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| 32 | |
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| 33 | if ~exist('two_focals_init'), |
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| 34 | two_focals_init = 0; |
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| 35 | end; |
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| 36 | |
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| 37 | if ~exist('est_aspect_ratio'), |
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| 38 | est_aspect_ratio = 1; |
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| 39 | end; |
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| 40 | |
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| 41 | check_active_images; |
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| 42 | |
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| 43 | if ~exist(['x_' num2str(ind_active(1)) ]), |
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| 44 | click_calib; |
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| 45 | end; |
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| 46 | |
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| 47 | |
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| 48 | fprintf(1,'\nInitialization of the intrinsic parameters - Number of images: %d\n',length(ind_active)); |
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| 49 | |
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| 50 | |
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| 51 | % Initialize the homographies: |
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| 52 | |
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| 53 | for kk = 1:n_ima, |
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| 54 | eval(['x_kk = x_' num2str(kk) ';']); |
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| 55 | eval(['X_kk = X_' num2str(kk) ';']); |
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| 56 | if (isnan(x_kk(1,1))), |
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| 57 | if active_images(kk), |
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| 58 | fprintf(1,'WARNING: Cannot calibrate with image %d. Need to extract grid corners first.\n',kk) |
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| 59 | fprintf(1,' Set active_images(%d)=1; and run Extract grid corners.\n',kk) |
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| 60 | end; |
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| 61 | active_images(kk) = 0; |
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| 62 | end; |
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| 63 | if active_images(kk), |
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| 64 | eval(['H_' num2str(kk) ' = compute_homography(x_kk,X_kk(1:2,:));']); |
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| 65 | else |
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| 66 | eval(['H_' num2str(kk) ' = NaN*ones(3,3);']); |
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| 67 | end; |
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| 68 | end; |
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| 69 | |
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| 70 | check_active_images; |
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| 71 | |
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| 72 | % initial guess for principal point and distortion: |
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| 73 | |
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| 74 | if ~exist('nx'), [ny,nx] = size(I); end; |
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| 75 | |
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| 76 | c_init = [nx;ny]/2 - 0.5; % initialize at the center of the image |
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| 77 | k_init = [0;0;0;0;0]; % initialize to zero (no distortion) |
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| 78 | |
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| 79 | |
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| 80 | |
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| 81 | % Compute explicitely the focal length using all the (mutually orthogonal) vanishing points |
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| 82 | % note: The vanihing points are hidden in the planar collineations H_kk |
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| 83 | |
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| 84 | A = []; |
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| 85 | b = []; |
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| 86 | |
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| 87 | % matrix that subtract the principal point: |
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| 88 | Sub_cc = [1 0 -c_init(1);0 1 -c_init(2);0 0 1]; |
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| 89 | |
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| 90 | for kk=1:n_ima, |
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| 91 | |
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| 92 | if active_images(kk), |
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| 93 | |
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| 94 | eval(['Hkk = H_' num2str(kk) ';']); |
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| 95 | |
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| 96 | Hkk = Sub_cc * Hkk; |
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| 97 | |
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| 98 | % Extract vanishing points (direct and diagonals): |
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| 99 | |
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| 100 | V_hori_pix = Hkk(:,1); |
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| 101 | V_vert_pix = Hkk(:,2); |
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| 102 | V_diag1_pix = (Hkk(:,1)+Hkk(:,2))/2; |
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| 103 | V_diag2_pix = (Hkk(:,1)-Hkk(:,2))/2; |
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| 104 | |
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| 105 | V_hori_pix = V_hori_pix/norm(V_hori_pix); |
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| 106 | V_vert_pix = V_vert_pix/norm(V_vert_pix); |
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| 107 | V_diag1_pix = V_diag1_pix/norm(V_diag1_pix); |
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| 108 | V_diag2_pix = V_diag2_pix/norm(V_diag2_pix); |
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| 109 | |
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| 110 | a1 = V_hori_pix(1); |
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| 111 | b1 = V_hori_pix(2); |
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| 112 | c1 = V_hori_pix(3); |
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| 113 | |
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| 114 | a2 = V_vert_pix(1); |
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| 115 | b2 = V_vert_pix(2); |
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| 116 | c2 = V_vert_pix(3); |
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| 117 | |
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| 118 | a3 = V_diag1_pix(1); |
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| 119 | b3 = V_diag1_pix(2); |
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| 120 | c3 = V_diag1_pix(3); |
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| 121 | |
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| 122 | a4 = V_diag2_pix(1); |
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| 123 | b4 = V_diag2_pix(2); |
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| 124 | c4 = V_diag2_pix(3); |
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| 125 | |
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| 126 | A_kk = [a1*a2 b1*b2; |
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| 127 | a3*a4 b3*b4]; |
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| 128 | |
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| 129 | b_kk = -[c1*c2;c3*c4]; |
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| 130 | |
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| 131 | |
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| 132 | A = [A;A_kk]; |
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| 133 | b = [b;b_kk]; |
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| 134 | |
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| 135 | end; |
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| 136 | |
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| 137 | end; |
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| 138 | |
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| 139 | |
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| 140 | % use all the vanishing points to estimate focal length: |
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| 141 | |
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| 142 | |
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| 143 | % Select the model for the focal. (solution to Gerd's problem) |
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| 144 | if ~two_focals_init |
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| 145 | if b'*(sum(A')') < 0, |
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| 146 | two_focals_init = 1; |
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| 147 | end; |
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| 148 | end; |
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| 149 | |
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| 150 | |
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| 151 | |
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| 152 | if two_focals_init |
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| 153 | % Use a two focals estimate: |
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| 154 | f_init = sqrt(abs(1./(inv(A'*A)*A'*b))); % if using a two-focal model for initial guess |
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| 155 | else |
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| 156 | % Use a single focal estimate: |
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| 157 | f_init = sqrt(b'*(sum(A')') / (b'*b)) * ones(2,1); % if single focal length model is used |
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| 158 | end; |
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| 159 | |
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| 160 | |
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| 161 | if ~est_aspect_ratio, |
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| 162 | f_init(1) = (f_init(1)+f_init(2))/2; |
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| 163 | f_init(2) = f_init(1); |
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| 164 | end; |
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| 165 | |
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| 166 | alpha_init = 0; |
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| 167 | |
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| 168 | %f_init = sqrt(b'*(sum(A')') / (b'*b)) * ones(2,1); % if single focal length model is used |
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| 169 | |
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| 170 | |
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| 171 | % Global calibration matrix (initial guess): |
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| 172 | |
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| 173 | KK = [f_init(1) alpha_init*f_init(1) c_init(1);0 f_init(2) c_init(2); 0 0 1]; |
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| 174 | inv_KK = inv(KK); |
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| 175 | |
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| 176 | |
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| 177 | cc = c_init; |
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| 178 | fc = f_init; |
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| 179 | kc = k_init; |
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| 180 | alpha_c = alpha_init; |
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| 181 | |
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| 182 | |
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| 183 | fprintf(1,'\n\nCalibration parameters after initialization:\n\n'); |
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| 184 | fprintf(1,'Focal Length: fc = [ %3.5f %3.5f ]\n',fc); |
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| 185 | fprintf(1,'Principal point: cc = [ %3.5f %3.5f ]\n',cc); |
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| 186 | fprintf(1,'Skew: alpha_c = [ %3.5f ] => angle of pixel = %3.5f degrees\n',alpha_c,90 - atan(alpha_c)*180/pi); |
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| 187 | fprintf(1,'Distortion: kc = [ %3.5f %3.5f %3.5f %3.5f %5.5f ]\n',kc); |
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