Photogrammetric stereoplotter

#This invention relates to a photogrammetric stereoplotter.

#It is well known art to photograph terrain stereoscopically and to then view the photographs through a stereo viewer usually comprising binoculars with a mirror system which reduces the spread of the optical axes to allow relatively larger photographs to be placed side-by-side for viewing at normal interocular distance.

#To be able to plot contours or other features from such a viewer it is known to use a pair of markers, generally referred to herein as "dots" which can be moved as a pair in a plane parallel to the photographs for the purpose of measuring position on a horizontal plane and can be varied in their spatial separation to determine perpendicular distance. For this purpose the dots are generally formed on a pair of transparent members carried on a cursor unit which dots move together in X and Y axes on a plane parallel to the photographs and generally perpendicular to the viewing axis but can be moved to vary the distance between them to measure altitude along a Z axis. These dots are so positioned that one is appropriately positioned to appear over each photograph.

#To enable the invention to be fully appreciated, a preferred embodiment thereof will now be described with reference to the accompanying drawings which are to be taken as illustrative only and in which:

#FIG. 1 is a block diagram which shows the invention applied to a digital stereoplotter, and

#FIG. 2 shows how the parallax correction is applied.

#In the form illustrated the binocular viewer 1 has mirrors 2--2 and 3--3 to enable a stereophoto pair 4-5 to be viewed, and with the binocular viewer 1 is associated a cursor unit 6 which is movable in X, Y axes parallel to the stereophoto axis 4-5 and carries the dots in a manner such that they are projected one each into the field of view of the binocular viewer 1 but themselves spaceable in distance in the plane of movement of the cursor unit to give binocular viewing along a Z axis normal to the X, Y axes.

#The movement of the cursor unit 6 is transferred to a stereogrammetric unit 7 which is linked to the computer 8 through the topographic X Y Z data unit 9, the computer 8 being fed extra required information by the operator such as contours, creeks, roads etc. through the topographic feature keyboard 10, but also by the voice recognition unit referred to later herein.

#The graphics unit 11 of the computer 8 feeds out to a display unit 12 and a printer 13, but also to an interface 14 from which the graphics 15 are fed to a cathode ray tube 16 which has a control 17 for brilliance and other adjustments and directs the trace through an optics train 18 to the beam splitter 19 which injects the plotted data such as contours, creeks, roads etc. to one side of the binocular viewer to visually transpose the trace onto the stereophoto.