Image analysis – Histogram processing – For setting a threshold
Patent
1982-12-10
1985-09-03
Boudreau, Leo H.
Image analysis
Histogram processing
For setting a threshold
250558, 350136, 356 2, 381110, 382 41, 382 60, G01C 1112, G06K 900
Patent
active
045397015
DESCRIPTION:
BRIEF SUMMARY
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 trace the contours the cursor unit is moved in the plane parallel to the picture surface with the dots spaced to represent stereoscopically a selected altitude, and a trace of the contour is made, in the case of an older form of the device, by a pantograph coupled to the cursor unit which produces the trace on a plotting surface adjacent to the stereo viewer, but it will be appreciated that the method of producing the trace can be varied such, for instance, as by varying the spatial separation of the dots while traversing the photographs to record the altitude changes of the terrain.
A problem which occurs is that, because the manipulation of the cursor unit is subject to human error, it is necessary periodically to check the trace produced by the pantograph pen, or other device which records the motion, and this requires the operator to leave the eye-pieces to look at the plotting sheet, or if using an integral plotting table, to peer between the equipment in front of the operator. Attention to the relative positions of contours, creeks and roads being drawn is important when these features run close together, as serious errors could occur from imperfections in the drafting process, or if the pen fails to mark.
The process is required to check for the completeness of a plotted feature and to correct errors in plotting by first erasing the error and then replotting the section. This problem is exacerbated when the stereoplotter is equipped with digital encoders to produce X, Y and Z coordinates of the plotted features as the operator is then required to look away even more frequently to enter computer commands and feature descriptions by a computer console device.
It is also known art to provide a video or computer generated cathode ray tube display either adjacent to the stereoplotter eye-pieces to minimise operator head movement or to superimpose these images into the stereo model field of view. However these devices do not provide an optimal solution in the display or superimposition method or the means to manipulate the displayed image without looking away from the eye-pieces.
As an example of the type of prior art in this field reference can be made to Canadian Pat. No. 1,020,341 granted to Her Majesty in right of Canada as represented by the National Research Council of Canada, which relates to an analytical plotter in the form of a stereo comparator in a closed loop with a computer in which the inputs are photographs and the output is digital or analogue data. A typewriter is used for the operator's input, through which the operator communicates with a computer by two handwheels for X and Y motion and a footwheel for elevation to move the photo-carrier. In this corresponding commands are generated and which the computer accepts from the handwheel and footwheel encoders via a buffer unit, and go via a servo-control-logic to photo-carrier servos so that the two photogr
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Galbreath Ronald E.
Harrison Bruce R.
Boudreau Leo H.
The Commonwealth of Australia
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