US National Large-scale City orthoimage standard initiative

The early procedures and algorithms for national digital orthophoto generation in the National Digital Orthophoto Program (NDOP) were based on earlier USGS mapping operations, such as field control, aerotriangulation (derived in the early 1920s), the quarter-quadrangle-centered (3.75 minutes of longitude and latitude in geographic extent), 1:40,000 aerial photographs, and 2.5 D digital elevation models. However, large-scale city orthophotos using early procedures have disclosed many shortcomings, e.g., ghost image, occlusion, shadow. Thus, to provide the technical base (algorithms, procedure) and experience needed for city large-scale digital orthophoto creation is essential for the near future national large-scale digital orthophoto deployment and the revision of the Standards for National Large-scale City Digital Orthophoto in National Digital Orthophoto Program (NDOP). This paper will report our initial research results as follows: (1) high-precision 3D city DSM generation through LIDAR data processing, (2) spatial objects/features extraction through surface material information and high-accuracy 3D DSM data, (3) 3D city model development, (4) algorithm development for generation of DTM-based orthophoto, and DBM-based orthophoto, (5) true orthophoto generation by merging DBM-based orthophoto and DTM-based orthophoto, and (6) automatic mosaic by optimizing and combining imagery from many perspectives.