Instant Relief with New Stereo Image Alternator

The recent development by the U.S. Geological Survey of Stereo Image Alternator (SIA) Illumination Systems for photogrammetric stereoplotters promises to extend the useful life of optical projection stereoplotter instruments by avoiding disadvantages of anaglyphic filter spectacles. Enabling a stereoplotter operator to see the stereo model more clearly, the SIA improves the operator's confidence and efficiency. While the SIA is an old idea, synchronization of shutters could not be reliably accomplished until electronically-pulsed stepping motors were employed. An improved SIA design for full-model projection stereoplotters, such as Balplex or Multiplex instruments, permits the opportunity of substituting a stereo photographic display for hand-made models. The resulting full-color, wide-angle, metrically accurate stereo model has promising applications in the fields of transportation route design, geology, pollution analysis, military engineering, public recreation areas, and regional and urban planning.