Volume 31, Issue 1 (January 1986)
The Use of Circular Scales in the Perspective Grid Technique of Making Photographic Measurements
The perspective grid technique commonly utilizes a square reference scale in the camera's field of view from which a grid pattern is graphically laid out in the photograph to measure distances lying in the same object plane as the scale. An improved technique described in this paper uses three circular scales as a basis for determining the X and Y coordinates of a point in the object plane from the x and y coordinate positions of its image in the photograph. This method offers the advantages of better accuracy and less tedious graphic methods of grid construction. A step-by-step procedure of constructing rectangular coordinate systems using either circular or square reference scales is presented.