Pennsylvania Spatial Data Access (PASDA) The Pennsylvania Geospatial Data Clearinghouse
Color Citywide digital orthophotography with a ground resolution of at various resolutions, georeferenced to the Pennsylvania State Plane Coordinate System, and delivered as individual and mosaicked raster images. The dataset consists of tiled orthogonal imagery produced from nadir images captured by various contractors during the months of April and May.
The dataset consists of tiled orthogonal imagery produced from nadir images captured by Pictometry International. Automatic aerial triangulation (AAT) was performed. The triangulated frames were rectified to a LiDAR derived DEM. Mosaicing was performed using an automatic seaming algorithm and manually edited to eliminate seams through elevated features where possible.
Flight plans were prepared to capture image frames with 60% forward overlap and 30% sidelap in order to provide sufficient overlap for automatic aerial triangulation and mitigation of building lean in orthophotography produced. Source imagery was acquired during times of optimal environmental conditions. Imagery will generally be captured when solar altitude is 30 degrees or greater and/or by using the most optimal four-hour window, except where capture season offers significantly longer window. Imagery was acquired with ground free of snow cover and deciduous vegetation less than 30% of full bloom. Frames with clouds were rejected and reflown. Any planned deviation from these conditions imposed by capture window constraints was discussed with client prior to commencement of acquisition.
Prior to the production of orthophotography, the vendor performed automatic aerial triangulation, utilizing the directly observed Exterior Orientations (EOs) and ground control points (GCPs), measured by a licensed surveyor, for the purpose of orienting the individual frames for creation of the final ortho imagery. In addition to the GCPs, sophisticated matching techniques was employed to automatically create tie points for use in performing a bundle adjustment. The vendor utilized best available Digital Terrain Models, combined with the calibrated camera interior orientations, ground control points, and triangulated EOs to rectify the images. When the rectification requires a resampling of the source imagery, a cubic convolution method was utilized.
Pennsylvania Spatial Data Access (PASDA)
Philadelphia Office of Innovation and Technology
Pictometry International Corp.
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