Page 11 - Digital Analysis of Remotely Sensed Imagery

x Co n t e n t s

5 Image Geometric Rectification . . . . . . . . . . . . . . . . . . . 143
5.1 Sources of Geometric Distortion . . . . . . . . . . . . . 144
5.1.1 Errors Associated with the Earth . . . . 144
5.1.2 Sensor Distortions . . . . . . . . . . . . . . . . 147
5.1.3 Errors Associated with the Platform . 149
5.1.4 Nature of Distortions . . . . . . . . . . . . . . 151
5.2 Projection and Coordinate Systems . . . . . . . . . . 151
5.2.1 UTM Projection . . . . . . . . . . . . . . . . . . . 152
5.2.2 NZMG . . . . . . . . . . . . . . . . . . . . . . . . . . 153

5.3 Fundamentals of Image Rectification . . . . . . . . . 156
5.3.1 Common Terms. . . . . . . . . . . . . . . . . . . 156
5.3.2 Image Geometric Transformation . . . 156
5.3.3 GCPs in Image Transformation . . . . . 158
5.3.4 Sources of Ground Control . . . . . . . . . 160

5.4 Rectification Models . . . . . . . . . . . . . . . . . . . . . . . 161
5.4.1 Affine Model . . . . . . . . . . . . . . . . . . . . . 161

5.4.2 Sensor-Specific Models . . . . . . . . . . . . 161

5.4.3 RPC Model. . . . . . . . . . . . . . . . . . . . . . . 162
5.4.4 Projective Transformation . . . . . . . . . . 162
5.4.5 Direct Linear Transform Model . . . . . 163
5.4.6 Polynomial Model . . . . . . . . . . . . . . . . 164
5.4.7 Rubber-Sheeting Model . . . . . . . . . . . . 164
5.5 Polynomial-Based Image Rectification . . . . . . . . 165

5.5.1 Transform Equations . . . . . . . . . . . . . . 165
5.5.2 Minimum Number of GCPs . . . . . . . . 167
5.5.3 Accuracy of Image Transform . . . . . . . 168
5.5.4 Creation of the Output Image . . . . . . . 172
5.6 Issues in Image Georeferencing . . . . . . . . . . . . . . 176
5.6.1 Impact of the Number of GCPs . . . . . 178
5.6.2 Impact of Image Resolution . . . . . . . . 180
5.6.3 Impact of GCP Quality . . . . . . . . . . . . 181
5.7 Image Orthorectification. . . . . . . . . . . . . . . . . . . . 183

5.7.1 Perspective versus Orthographic
Projection . . . . . . . . . . . . . . . . . . . . . . . . 184
5.7.2 Methods of Image Orthorectifi cation 185
5.7.3 Procedure of Orthorectification . . . . . 188

5.8 Image Direct Georeferencing . . . . . . . . . . . . . . . . 192
5.8.1 Transformation Equation . . . . . . . . . . . 192
5.8.2 Comparison with Polynomial Model 195
5.9 Image Subsetting and Mosaicking . . . . . . . . . . . 197
5.9.1 Image Subsetting . . . . . . . . . . . . . . . . . 197
5.9.2 Image Mosaicking . . . . . . . . . . . . . . . . 199
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201