System for producing orthophotographs

A system for producing orthophotographs, comprising:

• a recording device including a pair of projectors adapted to project a pair of stereoscopically related transparencies;
• an imaging surface spaced from said projectors;
• means for processing said projected transparencies so as to form on said imaging surface a stereoscopic image which is a stereomodel of a terrain;
• means for forming an optical reference point to be maintained on an apparent ground plane of said imaging surface;
• means for moving said optical reference in X- and Y-directions parallel to said imaging surface;
• means for further moving said imaging surface in a Z-direction orthogonal to said X- and Y-directions so as to maintain said optical reference on the apparent ground surface on said stereo models during scanning;
• and means for encoding X- and Y-positions of said optical reference and for encoding Z-positions on said imaging surface during scanning including means for generating digital signals representing said encoded positions;
• a reproducing device including a light projector;
• a platen spaced apart from said projector and carrying a photosenstive sheet;
• a transparency mount between said projector and said platen for supporting a transparency corresponding to said stereoscopic image;
• a screen having an aperture formed therein adjacent said platen and in view of said transparency mount;
• first means for moving said aperture in X- and Y-directions parallel to said platen for scanning said photosensitive sheet;
• and second means for moving said platen in a Z-direction orthogonal to said X- and Y-directions during scanning;
• and
• control means interfacing said recording device and said reproducing device, said control means including means for storing the digital signals representing (X, Y, Z) positions generated by said recording device during scanning;
• means for processing said encoded signals for compatability with said reproducing device;
• means for monitoring a X/Z slope of the terrain during playback thereof by said printer, and means responsive to said monitoring means for generating a slope correction signal;
• and means responsive to said processed data for controlling said first and second moving means of said reproducing device during exposure of said photosensitive sheet.

A method of producing orthophotographs from a pair of stereoscopically related transparencies, comprising in the steps of projecting a three dimensional image of a terrain model related to said transparencies on a imaging surface;

• causing an optical reference to scan said surface in zig-zag fashion;
• controlling the distance between said optical reference and said imaging surface during scanning to maintain said reference in intersection with an apparent ground surface of said terrain image to define terrain profiles;
• digitally encoding X- and Y-coordinates parallel to said imaging surface of said optical reference during scanning;
• further digitally encoding Z-coordinates orthogonal to said imaging surface of said optical reference;
• monitoring Y/Z slope of each of said profiles during scanning of said imaging surface;
• detecting each occurrence of an excessive Y/Z slope;
• counting each of said occurrences;
• providing an indication of a predetermined number of detected occurrences;
• formatting the digitally encoded X, Y and Z coordinates into an individual data block for each terrain profile;
• recording said data blocks on a storage means;
• and reading out said stored data blocks to control scanning of a photosensitive sheet during exposure of said sheet to one of said transparencies in an orthophotographic printer.

A method of producing orthophotographs from a pair of stereoscopically related transparencies, comprising the steps of projecting a three dimensional image of a terrain model related to said transparencies on an imaging surface;

• causing an optical reference to scan said surface in zig-zag fashion;
• controlling the distance between said optical reference and said imaging surface during scanning to maintain said reference in intersection with an apparent ground surface of said terrain image to define terrain profiles;
• digitally encoding X- and Y-coordinates parallel to said imaging surface of said optical reference during scanning;
• further digitally encoding Z-coordinates orthogonal to said imaging surface of said optical reference;
• monitoring X/Z slope during reading out of said stored data blocks;
• generating slope correction signals for use with slope correction optics;
• formatting the digitally encoded X, Y, and Z coordinates into an individual data block for each terrain profile;
• recording said data blocks on a storage means;
• and reading out said stored data blocks to control scanning of a photosensitive sheet during exposure of said sheet to one of said transparencies in an orthophotographic printer.