The aerial triangulation (AT) block for the Rochester NY Urban Region, consisting of 18 flightlines and 864 images with nominal 60% forward overlap and 25% sidelap was captured in one DMC flight mission. The AT adjustment was supported by direct georeferencing data collected via the Applanix POS/AV 510 combined carrier-phase GPS + inertial measurement unit (IMU) and was performed using Z/I Imaging's ISAT (ImageStation Automatic Triangulation) software version 4.3.06. The project was referenced to the North American Datum of 1983/1996 (NAD83/96), New York State Plane Coordinates, Central Zone (3102) horizontally and to the North American Vertical Datum of 1988 (NAVD88) vertically. Units are in US Survey Feet.
27 survey control points were included in the adjustment, giving a control point density and geometry with a high level of redundancy for a block adjustment supported by the Applanix POS/AV 510.
The initial settings for the full XYZ survey control points were at 0.5 pixel in XY and 0.8 pixel in Z. These were stepped-down in stages of 50% until acceptable final RMS and max residual values were achieved. Their final settings were
0.11 ft in XY and 0.18 ft in Z.
Existing DEM data is clipped into manageable files and reviewed for potential problems or needed updates. The existing DEM is densified where needed using ImageStation Stereo Display. Bridge aprons are added or modified to project specifications. The DEM is modified where any significant changes in the terrain are evident. Breaklines are added where necessary to facilitate orthoproduction.
The DMC digital imagery is color balanced and converted from the 12 bit to 8 bits per band using ImageStation Raster Utilities. The 8 bit digital imagery is rectified to produce orthophotography using ImageStation OrthoPro. A quality control review is performed on the orthophotos. They are visually inspected for horizontal accuracy, tonal balancing, smears, relief displacement, artifacts, etc. The horizontal accuracy is assessed by comparing each GPS ground control point to the same photoidentifiable X,Y coordinate on the orthophoto and by comparing edge and mosaic seamline matches between adjacent orthophotos looking for displacement.
Once the orthophotos have passed the quality control review, seamlines are manually created between the overlapping parts of the orthophotos. These seamlines have a 15 pixel feathering swath that ensures a seamless, color balanced transition between adjacent orthophotos in the mosaic. Multiple orthophoto chips are mosaicked then clipped to final orthophoto tiles. The final mosaic tiles are in uncompressed GeoTIFF format.
The mosaic orthophoto tiles are checked for image quality. They are individually inspected for content, misalignments along mosaic seamlines, void areas and artifacts. The remaining errors are corrected using Adobe Photoshop in an interactive editing session. Orthophoto tiles with major errors are rejected. Orthophoto tiles with major errors are reprocessed once the error source is determined. A final LUT is applied to all mosaics to meet client-approved radiometry.