1 | /** file: rodirgues.c |
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2 | ** author: Andrea Vedaldi |
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3 | ** description: Rodrigues formulas |
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4 | **/ |
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5 | |
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6 | /* AUTORIGHTS |
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7 | Copyright (C) 2006 Andrea Vedaldi |
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8 | |
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9 | This file is part of VLUtil. |
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10 | |
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11 | VLUtil is free software; you can redistribute it and/or modify |
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12 | it under the terms of the GNU General Public License as published by |
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13 | the Free Software Foundation; either version 2, or (at your option) |
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14 | any later version. |
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15 | |
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16 | This program is distributed in the hope that it will be useful, |
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17 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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18 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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19 | GNU General Public License for more details. |
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20 | |
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21 | You should have received a copy of the GNU General Public License |
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22 | along with this program; if not, write to the Free Software Foundation, |
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23 | Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. |
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24 | */ |
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25 | |
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26 | #include"rodrigues.h" |
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27 | #include<math.h> |
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28 | #include<limits.h> |
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29 | |
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30 | /** @brief Rodrigues' formula |
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31 | **/ |
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32 | void |
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33 | vl_rodrigues(double* R_pt, double* dR_pt, const double* om_pt) |
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34 | { |
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35 | /* |
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36 | Let |
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37 | |
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38 | th = |om|, r=w/th, |
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39 | sth=sin(th), cth=cos(th), |
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40 | ^om = hat(om) |
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41 | |
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42 | Then the rodrigues formula is an expansion of the exponential |
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43 | function: |
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44 | |
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45 | rodrigues(om) = exp ^om = I + ^r sth + ^r^2 (1 - cth). |
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46 | |
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47 | The derivative can be computed by elementary means and |
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48 | results: |
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49 | |
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50 | d(vec rodrigues(om)) sth d ^r 1 - cth d (^r)^2 |
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51 | -------------------- = ---- ----- + ------- -------- + |
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52 | d om^T th d r^T th d r^T |
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53 | |
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54 | sth 1 - cth |
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55 | + vec^r (cth - -----) + vec^r^2 (sth - 2-------)r^T |
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56 | th th |
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57 | */ |
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58 | |
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59 | #define OM(i) om_pt[(i)] |
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60 | #define R(i,j) R_pt[(i)+3*(j)] |
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61 | #define DR(i,j) dR_pt[(i)+9*(j)] |
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62 | |
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63 | const double small = 1e-6 ; |
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64 | |
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65 | double th = sqrt( OM(0)*OM(0) + |
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66 | OM(1)*OM(1) + |
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67 | OM(2)*OM(2) ) ; |
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68 | |
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69 | if( th < small ) { |
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70 | R(0,0) = 1.0 ; R(0,1) = 0.0 ; R(0,2) = 0.0 ; |
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71 | R(1,0) = 0.0 ; R(1,1) = 1.0 ; R(1,2) = 0.0 ; |
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72 | R(2,0) = 0.0 ; R(2,1) = 0.0 ; R(2,2) = 1.0 ; |
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73 | |
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74 | if(dR_pt) { |
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75 | DR(0,0) = 0 ; DR(0,1) = 0 ; DR(0,2) = 0 ; |
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76 | DR(1,0) = 0 ; DR(1,1) = 0 ; DR(1,2) = 1 ; |
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77 | DR(2,0) = 0 ; DR(2,1) = -1 ; DR(2,2) = 0 ; |
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78 | |
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79 | DR(3,0) = 0 ; DR(3,1) = 0 ; DR(3,2) = -1 ; |
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80 | DR(4,0) = 0 ; DR(4,1) = 0 ; DR(4,2) = 0 ; |
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81 | DR(5,0) = 1 ; DR(5,1) = 0 ; DR(5,2) = 0 ; |
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82 | |
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83 | DR(6,0) = 0 ; DR(6,1) = 1 ; DR(6,2) = 0 ; |
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84 | DR(7,0) = -1 ; DR(7,1) = 0 ; DR(7,2) = 0 ; |
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85 | DR(8,0) = 0 ; DR(8,1) = 0 ; DR(8,2) = 0 ; |
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86 | } |
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87 | return ; |
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88 | } |
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89 | |
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90 | { |
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91 | double x = OM(0) / th ; |
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92 | double y = OM(1) / th ; |
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93 | double z = OM(2) / th ; |
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94 | |
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95 | double xx = x*x ; |
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96 | double xy = x*y ; |
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97 | double xz = x*z ; |
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98 | double yy = y*y ; |
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99 | double yz = y*z ; |
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100 | double zz = z*z ; |
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101 | |
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102 | const double yx = xy ; |
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103 | const double zx = xz ; |
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104 | const double zy = yz ; |
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105 | |
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106 | double sth = sin(th) ; |
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107 | double cth = cos(th) ; |
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108 | double mcth = 1.0 - cth ; |
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109 | |
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110 | R(0,0) = 1 - mcth * (yy+zz) ; |
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111 | R(1,0) = sth*z + mcth * xy ; |
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112 | R(2,0) = - sth*y + mcth * xz ; |
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113 | |
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114 | R(0,1) = - sth*z + mcth * yx ; |
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115 | R(1,1) = 1 - mcth * (zz+xx) ; |
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116 | R(2,1) = sth*x + mcth * yz ; |
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117 | |
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118 | R(0,2) = sth*y + mcth * xz ; |
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119 | R(1,2) = - sth*x + mcth * yz ; |
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120 | R(2,2) = 1 - mcth * (xx+yy) ; |
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121 | |
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122 | if(dR_pt) { |
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123 | double a = sth / th ; |
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124 | double b = mcth / th ; |
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125 | double c = cth - a ; |
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126 | double d = sth - 2*b ; |
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127 | |
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128 | DR(0,0) = - d * (yy+zz) * x ; |
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129 | DR(1,0) = b*y + c * zx + d * xy * x ; |
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130 | DR(2,0) = b*z - c * yx + d * xz * x ; |
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131 | |
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132 | DR(3,0) = b*y - c * zx + d * xy * x ; |
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133 | DR(4,0) = -2*b*x - d * (zz+xx) * x ; |
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134 | DR(5,0) = a + c * xx + d * yz * x ; |
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135 | |
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136 | DR(6,0) = b*z + c * yx + d * zx * x ; |
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137 | DR(7,0) = -a - c * xx + d * zy * x ; |
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138 | DR(8,0) = -2*b*x - d * (yy+xx) * x ; |
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139 | |
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140 | DR(0,1) = -2*b*y - d * (yy+zz) * y ; |
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141 | DR(1,1) = b*x + c * zy + d * xy * y ; |
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142 | DR(2,1) = -a - c * yy + d * xz * y ; |
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143 | |
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144 | DR(3,1) = b*x - c * zy + d * xy * y ; |
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145 | DR(4,1) = - d * (zz+xx) * y ; |
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146 | DR(5,1) = b*z + c * xy + d * yz * y ; |
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147 | |
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148 | DR(6,1) = a + c * yy + d * zx * y ; |
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149 | DR(7,1) = b*z - c * xy + d * zy * y ; |
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150 | DR(8,1) = -2*b*y - d * (yy+xx) * y ; |
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151 | |
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152 | DR(0,2) = -2*b*z - d * (yy+zz) * z ; |
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153 | DR(1,2) = a + c * zz + d * xy * z ; |
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154 | DR(2,2) = b*x - c * yz + d * xz * z ; |
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155 | |
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156 | DR(3,2) = -a - c * zz + d * xy * z ; |
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157 | DR(4,2) = -2*b*z - d * (zz+xx) * z ; |
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158 | DR(5,2) = b*y + c * xz + d * yz * z ; |
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159 | |
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160 | DR(6,2) = b*x + c * yz + d * zx * z ; |
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161 | DR(7,2) = b*y - c * xz + d * zy * z ; |
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162 | DR(8,2) = - d * (yy+xx) * z ; |
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163 | } |
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164 | } |
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165 | |
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166 | #undef OM |
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167 | #undef R |
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168 | #undef DR |
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169 | |
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170 | } |
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171 | |
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172 | /** @brief Inverse Rodrigues formula |
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173 | ** |
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174 | ** This function computes the Rodrigues formula of the |
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175 | ** argument @a om_pt. The result is stored int the matrix |
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176 | ** @a R_pt. If @a dR_pt is non null, then the derivative |
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177 | ** of the Rodrigues formula is computed and stored into |
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178 | ** the matrix @a dR_pt. |
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179 | ** |
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180 | ** @param R_pt pointer to a 3x3 matrix (array of 9 doubles). |
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181 | ** @param dR_pt pointer to a 9x3 matrix (array of 27 doubles). |
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182 | ** @param om_pt pointer to a 3 vector (array of 3 dobules). |
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183 | **/ |
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184 | |
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185 | void vl_irodrigues(double* om_pt, double* dom_pt, const double* R_pt) |
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186 | { |
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187 | /* |
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188 | tr R - 1 1 [ R32 - R23 ] |
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189 | th = cos^{-1} --------, r = ------ [ R13 - R31 ], w = th r. |
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190 | 2 2 sth [ R12 - R21 ] |
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191 | |
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192 | sth = sin(th) |
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193 | |
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194 | dw th*cth-sth dw th [di3 dj2 - di2 dj3] |
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195 | ---- = ---------- r, ---- = ----- [di1 dj3 - di3 dj1]. |
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196 | dRii 2 sth^2 dRij 2 sth [di1 dj2 - di2 dj1] |
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197 | |
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198 | trace(A) < -1 only for small num. errors. |
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199 | */ |
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200 | |
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201 | #define OM(i) om_pt[(i)] |
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202 | #define DOM(i,j) dom_pt[(i)+3*(j)] |
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203 | #define R(i,j) R_pt[(i)+3*(j)] |
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204 | #define W(i,j) W_pt[(i)+3*(j)] |
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205 | |
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206 | const double small = 1e-6 ; |
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207 | |
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208 | double th = acos |
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209 | (0.5*(MAX(R(0,0)+R(1,1)+R(2,2),-1.0) - 1.0)) ; |
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210 | |
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211 | double sth = sin(th) ; |
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212 | double cth = cos(th) ; |
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213 | |
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214 | if(fabs(sth) < small && cth < 0) { |
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215 | /* |
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216 | we have this singularity when the rotation is about pi (or -pi) |
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217 | we use the fact that in this case |
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218 | |
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219 | hat( sqrt(1-cth) * r )^2 = W = (0.5*(R+R') - eye(3)) |
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220 | |
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221 | which gives |
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222 | |
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223 | (1-cth) rx^2 = 0.5 * (W(1,1)-W(2,2)-W(3,3)) |
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224 | (1-cth) ry^2 = 0.5 * (W(2,2)-W(3,3)-W(1,1)) |
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225 | (1-cth) rz^2 = 0.5 * (W(3,3)-W(1,1)-W(2,2)) |
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226 | */ |
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227 | |
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228 | double W_pt [9], x, y, z ; |
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229 | W_pt[0] = 0.5*( R(0,0) + R(0,0) ) - 1.0 ; |
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230 | |
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231 | W_pt[0] = 0.5*( R(1,0) + R(0,1) ) ; |
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232 | W_pt[0] = 0.5*( R(2,0) + R(0,2) ); |
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233 | |
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234 | W_pt[0] = 0.5*( R(0,1) + R(1,0) ); |
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235 | W_pt[0] = 0.5*( R(1,1) + R(1,1) ) - 1.0; |
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236 | W_pt[0] = 0.5*( R(2,1) + R(1,2) ); |
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237 | |
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238 | W_pt[0] = 0.5*( R(0,2) + R(2,0) ) ; |
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239 | W_pt[0] = 0.5*( R(1,2) + R(2,1) ) ; |
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240 | W_pt[0] = 0.5*( R(2,2) + R(2,2) ) - 1.0 ; |
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241 | |
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242 | /* these are only absolute values */ |
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243 | x = sqrt( 0.5 * (W(0,0)-W(1,1)-W(2,2)) ) ; |
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244 | y = sqrt( 0.5 * (W(1,1)-W(2,2)-W(0,0)) ) ; |
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245 | z = sqrt( 0.5 * (W(2,2)-W(0,0)-W(1,1)) ) ; |
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246 | |
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247 | /* set the biggest component to + and use the element of the |
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248 | ** matrix W to determine the sign of the other components |
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249 | ** then the solution is either (x,y,z) or its opposite */ |
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250 | if( x >= y && x >= z ) { |
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251 | y = (W(1,0) >=0) ? y : -y ; |
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252 | z = (W(2,0) >=0) ? z : -z ; |
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253 | } else if( y >= x && y >= z ) { |
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254 | z = (W(2,1) >=0) ? z : -z ; |
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255 | x = (W(1,0) >=0) ? x : -x ; |
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256 | } else { |
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257 | x = (W(2,0) >=0) ? x : -x ; |
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258 | y = (W(2,1) >=0) ? y : -y ; |
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259 | } |
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260 | |
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261 | /* we are left to chose between (x,y,z) and (-x,-y,-z) |
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262 | ** unfortunately we cannot (as the rotation is too close to pi) and |
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263 | ** we just keep what we have. */ |
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264 | { |
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265 | double scale = th / sqrt( 1 - cth ) ; |
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266 | OM(0) = scale * x ; |
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267 | OM(1) = scale * y ; |
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268 | OM(2) = scale * z ; |
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269 | |
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270 | if( dom_pt ) { |
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271 | int k ; |
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272 | for(k=0; k<3*9; ++k) |
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273 | dom_pt[k] = NAN ; |
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274 | } |
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275 | return ; |
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276 | } |
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277 | |
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278 | } else { |
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279 | double a = (fabs(sth) < small) ? 1 : th/sin(th) ; |
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280 | double b ; |
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281 | OM(0) = 0.5*a*(R(2,1) - R(1,2)) ; |
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282 | OM(1) = 0.5*a*(R(0,2) - R(2,0)) ; |
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283 | OM(2) = 0.5*a*(R(1,0) - R(0,1)) ; |
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284 | |
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285 | if( dom_pt ) { |
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286 | if( fabs(sth) < small ) { |
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287 | a = 0.5 ; |
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288 | b = 0 ; |
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289 | } else { |
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290 | a = th/(2*sth) ; |
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291 | b = (th*cth - sth)/(2*sth*sth)/th ; |
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292 | } |
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293 | |
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294 | DOM(0,0) = b*OM(0) ; |
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295 | DOM(1,0) = b*OM(1) ; |
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296 | DOM(2,0) = b*OM(2) ; |
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297 | |
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298 | DOM(0,1) = 0 ; |
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299 | DOM(1,1) = 0 ; |
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300 | DOM(2,1) = a ; |
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301 | |
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302 | DOM(0,2) = 0 ; |
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303 | DOM(1,2) = -a ; |
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304 | DOM(2,2) = 0 ; |
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305 | |
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306 | DOM(0,3) = 0 ; |
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307 | DOM(1,3) = 0 ; |
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308 | DOM(2,3) = -a ; |
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309 | |
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310 | DOM(0,4) = b*OM(0) ; |
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311 | DOM(1,4) = b*OM(1) ; |
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312 | DOM(2,4) = b*OM(2) ; |
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313 | |
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314 | DOM(0,5) = a ; |
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315 | DOM(1,5) = 0 ; |
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316 | DOM(2,5) = 0 ; |
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317 | |
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318 | DOM(0,6) = 0 ; |
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319 | DOM(1,6) = a ; |
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320 | DOM(2,6) = 0 ; |
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321 | |
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322 | DOM(0,7) = -a ; |
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323 | DOM(1,7) = 0 ; |
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324 | DOM(2,7) = 0 ; |
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325 | |
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326 | DOM(0,8) = b*OM(0) ; |
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327 | DOM(1,8) = b*OM(1) ; |
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328 | DOM(2,8) = b*OM(2) ; |
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329 | } |
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330 | } |
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331 | |
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332 | #undef OM |
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333 | #undef DOM |
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334 | #undef R |
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335 | #undef W |
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336 | } |
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