Clifford W. Greve 1995 The U.S. Geological Survey is converting its primary map production and revision operations to use digital photogrammetric techniques. The primary source of data for these operations is the digital orthophoto quadrangle derived from National Aerial Photography Program images. These digital orthophotos are used on workstations that permit comparison of existing vector and raster data with the orthophoto and interactive collection and revision of the vector data. application/pdf en Society of Photo-Optical Instrumentation Engineers Digital photogrammetry at the U.S. Geological Survey text