The traditional method of making true digital orthophoto map is orthophoto correction using digital surface model. Tall buildings will be blocked due to the displacement of image points in orthophoto correction. This paper studies the generation method of true digital orthophoto map based on 3D point cloud geometry, and completes the production of true digital orthophoto map through point cloud registration, absolute orientation, equal interval sampling, vertical projection and texture mapping. This paper studies the equal interval sampling method and vertical projection method in this process, which reduces the time of traditional methods in masking detection and repair, it has high automation.
The increasing developments in Unmanned Aerial Vehicles (UAVs) platforms and associated sensing technologies have
widely promoted UAVs remote sensing application. UAVs, especially low-cost UAVs, limit the sensor payload in
weight and dimension. Mostly, cameras on UAVs are panoramic, fisheye lens, small-format CCD planar array camera,
unknown intrinsic parameters and lens optical distortion will cause serious image aberrations, even leading a few meters
or tens of meters errors in ground per pixel. However, the characteristic of high spatial resolution make accurate geolocation
more critical to UAV quantitative remote sensing research. A method for MCC4-12F Multispectral Imager
designed to load on UAVs has been developed and implemented. Using multi-image space resection algorithm to assess
geometric calibration parameters of random position and different photogrammetric altitudes in 3D test field, which is
suitable for multispectral cameras. Both theoretical and practical accuracy assessments were selected. The results of
theoretical strategy, resolving object space and image point coordinate differences by space intersection, showed that
object space RMSE were 0.2 and 0.14 pixels in X direction and in Y direction, image space RMSE were superior to 0.5
pixels. In order to verify the accuracy and reliability of the calibration parameters,practical study was carried out in
Tianjin UAV flight experiments, the corrected accuracy validated by ground checkpoints was less than 0.3m. Typical
surface reflectance retrieved on the basis of geo-rectified data was compared with ground ASD measurement resulting 4%
discrepancy. Hence, the approach presented here was suitable for UAV multispectral imager.
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