US3777055A

US3777055A - Hexagonal patch printing for orthophoto printers

Info

Publication number: US3777055A
Application number: US00231574A
Authority: US
Inventors: G Hobrough
Original assignee: HOBROUGH Ltd
Current assignee: HOBROUGH Ltd
Priority date: 1972-03-03
Filing date: 1972-03-03
Publication date: 1973-12-04
Anticipated expiration: 1990-12-04
Also published as: CA975947A

Abstract

A system is described for providing video signals from left and right stereo photographs which correspond to discrete, homologous areas thereof and which are compensated for parallax and other visual distortion errors. To print a portion of an orthophotograph corresponding to this video signal, a mask defining an hexagonal patch is interposed in the light path between a cathode ray tube for displaying the video signal, and a photographic negative. To construct the entire orthophoto, the negative is mounted on a photo printing device which moves the negative in discrete increments corresponding to selective scanning of corresponding areas in the left and right stero photographs.

Description

United States Patent 1 Hobrough HEXAGONAL PATCH PRINTING FOR ORTHOPHOTO PRINTERS [75] Inventor: Gilbert L. Hobrough, Vancouver,

British Columbia, Canada [73] Assignee: Hobrough Limited, Vancouver,

British Columbia, Canada [22] Filed: Mar. 3, 1972 [21] Appl. No.: 231,574

[ Dec.4, 1973 3/1972 Kowalski 250/220 SP 4/1960 Bamet 356/2 [5 7 ABSTRACT A system is described for providing video signals from left and right stereo photographs which correspond to discrete, homologous areas thereof and which are compensated for parallax and other visual distortion errors. To print a portion of an orthophotograph corresponding to this video signal, a mask defining an hexagonal patch is interposed in the light path between a cathode ray tube for displaying the video sig nal, and a photographic negative. To construct the entire orthophoto, the negative is mounted on a photo printing device which moves the negative in discrete increments corresponding to selective scanning of corresponding areas in the left and right stero photographs.

7 Claims, 6 Drawing Figures F/PDM 5a .s'c/l/v 59 GENE/e4 roe VIDEO 55 01/7 PUT PATENTED DEC 4 I975 SHEET 1 BF 3 PATENTEDnzc 4 7975' SHEET '2 BF 3 GE/YEKA TOE 56 VIDEO 7 OUTPUT PAIENTEDBEc 4 ms 3,777,055

- SHEET 3 OF 3 HEXAGONAL PATCH PRINTING FOR ORTHOPHOTO PRINTERS FIELD OF THE INVENTION This invention. generally relates to the field of automatic orthophoto printers, and more particularly, to an improvement inthe printing of orthophotographs.

BACKGROUND OF THE'INVENTION An improved system which operates automatically to provide an orthophotograph for one or more pairs of stereo aerial photographs is described in my copending application entitled AutomaticOrthophoto Printer," U.'S. Ser. No. 760,435, filed'Sept. 18, 1968, now US. Pat No. 3,659,939 which is also assigned to the assignee of the present invention. This system greatly reduces the time necessary to produce an orthophotograph and includes first and second photo-scanning devices which are operated in synchronism to provide video signals for each of the two photographs making upa stereo pair. Homologous areas of the photographs are scanned, with the portion under consideration being termed the correlation zone. In order to reduce X and Y parallax of the video signalswithin the correlation zone, the system zincludes a correlation network' which operates on the video signals todetermine the amount of parallax error, and image transformation circuitry and raster shaping circuits controlled thereby for altering the scanning patterns of the two photoscanning devices. Oncethe correlation zones of the two photographs have beenbrought: into approximate registryby appropriatev photo positioning devices, the system alters the scan pattern of one or both photoscanning devices toreduce parallax and other errors to zero. One of the resultant video signals, which represents one image ofthe correlation zone, is supplied to a cathode ray-tube for imprinting on the photographic negative. By investigating a number of correlation zones, an orthophotograph can be formed.

In order to increase the speed of orthphotograph production, each correlation zone should be as large as possible. The correlation zone size is determined by the image transformation capability of the system, and the printing method employed. With'respect to the former, the complexity of the transformation that is required to eliminate parallax error .generallyincreases with an increase in the area of the correlation zone. Accordingly, even withthe 50th-order transformation capability of the system described in the aforementioned copending patent application, there is a finite limit upon this area.

The path method of printing has proved itself adaptable to systems such as described in the aforementioned copending patent application. In the patch method, an image corresponding to the entire correlation zone is displayedon the face of a cathode ray tube and imprinted at one point in time after transformation has been completed.

However, the patch printing method is subject to limitations on the size and shape of the correlation zone due to (a) distortions in the reproduced image at the extremities of the CRTs scan, (b) limitations of the correlation process, and v(c) limitations in matching patch boundaries mechanically and optically.

It is accordingly an object'of this invention to provide an improved patch printing :method for an automatic orthophoto printer.

Another object of this invention is to provide an improvement for an automatic orthophoto printing system which includes means for producing orthophotographs by the patch printing method in which the aforementioned limitationsv are minimized.

SUMMARY OF THE INVENTION These objects and others are achieved by providing means defining a hexagonal mask in a light path between the face of a cathode ray tube on which the transformed image is displayed and. the emulsion surface of a negative comprising the desired orthophoto.

DESCRIPTION OF THE DRAWINGS The above as well as additional advantages and objects will be more clearly understood with reference to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram showing an automatic orthophoto printing system;

FIG. 2 is a pictorial view showing the output cathode ray tubeand orthophoto printing mechanism of FIG. 1;

FIG. 3 is a plan view of the hexagonal-masbdefining means shown in FIG. 2;

FIG. 4 is another, exploded view of the apparatus illustratedin FIG. 2;

FIG. 5 is a reproduction of an orthophotograph which was producedusingthe patch printing method of the prior art; and

FIG. 6 isa representation of the same orthophotograph but producedusingthe hexagonal patch printing method of this invention.

DESCRIPTION OF A PREFERRED EMBODIMENT FIG. 1 is a system'diagram of the elements of a preferred embodiment-of the invention shown as an automated analytical plotter. Diapositives 12A and 128 corresponding to the stereo aerial photographs are mounted .on the carriages l7 and 18 of the scanner and

plate transport assemblies

41 and 42. The plates are adapted for movement in the X and Y directions by the X drive motors l9 and 20 and the

Y drive motors

21 and 22.

Light sources

23 and 24 illuminate the diapositives and provide light for the scanners 25 and 26 (which can be conventional TV pickup units). A scanning'printer 43 contains a cathode ray tube 59 and an optical system for printing on sensitive film 43A. A computer 29 which can be any of a number available on the market solves the basic resection-intersection equations and delivers stage coordinate commands to the

scanners

41 and 42 and to printer 43, on

lines

44X, 44Y, 45X, 45Y, and 46X, 46Y, respectively. The electronic viewer 47 enables an operator to observe the images being scanned. A steering control 48 delivers instructions to the computer during manual operations. The electronic correlator 49 generates X and Y parallax error signals in response to timing differences between corresponding elements of the left and right 'video signals on output lines 50 and 51 from

scanners

25 and 26.

The operation of the system illustrated in FIG. 1 is as follows. First, a sequential program establishes a pair of model coordinates for examination. Stage coordinate signals are delivered to the printer 43 along lines 46X, and 46Y, causing the sensitive film 43A in the printer 43 toassume a position corresponding to the selected model coordinate. Second, stage coordinates for the left and right scanners are computed on the basis of an initial or arbitrary terrain height (Z) evaluation for the center of the scanned area and such coordinate signals are delivered on

lines

44X, 44Y and 45X, 45Y to actuate the

transports

41, 42, respectively. The correlator operates on the left and right video signals, on lines 50 and 51 respectively, to determine the X and Y parallax errors of the scanned area. The X parallax error signal from the correlator is delivered to the computer along line 52. On the analysis of this signal, the computer center can order a modification of the initial Z value in a direction that will reduce the center X parallax error to zero. The computer re-evaluates the stage coordinates of the scanners on the basis of the new Z value and delivers modified stage coordinates to the left and right scanners on

lines

44X, 44Y and 45X, 45Y respectively. The motion of the transport is electronically compensated for by the simultaneous cancellation from the memory of the correlator of this center-point Z value. In this manner, the range of the correlators memory is optimized about the center point of the scanned area. The process of analysis of the X parallax error on line 52 and the determination of a new Z coordinate continues iteratively until the center-point X error (a zero-order signal) has been reduced to an acceptable level that has made optimum use of the correlators memory. An average Y parallax signal on line 53 is also delivered to the computer and is used during setup and orientation of the model to generate new stage coordinates for the scanners in the Y direction. After orientation the Y parallax signal should be zero I but during compilation of the model the computer responds to Y parallax error signals to compensate for the effects of film shrinkage, optical distortions, etc.

The printer 43 shown in FIG. 1 produces an orthophotograph on sensitive film 43A therein. The cathode ray tube in the printer 43 is scanned synchronously with the

scanners

25 and 26 and one of the video signals from the scannersis used to modulate the lightintensity of the scanning spot in the printer. In FIG. 1, the video signal from a left or right scanner is delivered along line 50 or 51 through the scanner selector switch 54 and along line 55 to printer 43. Normally, the left video signal is selected for printing areas towards the left of the model and the right video signal is selected for printing areas towards the right of the model. For this purpose a left-right signal from computer 29 is delivered to selector switch 54 along line 55A. The computer also delivers an inhibit signal on line 56A that is combined in summing circuit 57A with the video signal from switch 54. The inhibit signal blanks the light output from cathode ray tube 59 to zero except during the desired printing period.

The scan generator 56 produces deflection wave forms required for scanning the diapositives and sensitive film. Te scanning pattern or raster is normally square, but as discussed below the raster signals for

scanners

25 and 26 are shaped as required for registration. In FIG. 1 the deflection wave forms from scan generator 56 are delivered along line 58 to the printing cathode ray tube 59, and via

lines

57 and 59A to the raster shaper 62 for the left scanner camera, and via

lines

57 and 60 to the raster shaper 63 for the right scanner camera. Scanning reference signals are delivered via

lines

57 and 61 to the correlator 49.

The raster shapers 62 and 63 both receive AZ signals from the correlator 49 along lines 64 and 65. Raster shapers 62 and 63 also receive signals from computer 29 along lines 66 and 67 respectively.

The raster shapers 62 and 63 modify the square raster wave forms from the scan generator delivered on

lines

59A and 60 to produce raster wave forms on lines 66A and 67A that produce in

scanners

25 and 26 rasters that are distorted by high order transformations from their normal square shape. By this means the left and right stereo images are transformed in such a manner that the video signals on lines and 51 become more similar, and the image in the scanning printer 43 reflects the corrections for scale and other distortions arising out of nonorthogonal conditions when the pictures were taken.

A parallel line or TV scanning pattern can be conveniently used in the system of the present invention. The scanning lines run parallel to the X axis of the model so that the X parallax may be detected simply by means of timing differences between the left and right video signals. The number of transformation elements, i.e., measurements of time differences in the raster, is dictated by the degree of distortion or transformation that must be applied to accommodate terrain irregularities. The transformation degree that can be achieved is very high, e.g., equivalent to that of a SOth-order system, and is not a limiting fastor to raster size. The number of transformation elements, the size of the raster, and the video information content of the raster are a function of the precision with which the scanning rasters can be controlled. Various system parameters can be adjusted to optimize precisionlimitations. If a standard scanning raster is used, then the magnification from the film plane to the scanning raster can be selected to optimize the system resolution. A raster conforming to American TV standards is convenient for the subject invention.

The American TV (RETMA) raster parameters referred to are as follows:

Line period 63.5 microseconds Field period 1/60 second Single interlace with two fields per frame, and thus a frame period 1/30 second Aspect ratio width/height The ends of the raster can be masked to provide a square format.

Although the

scanners

41, 42 and scanning printer 43 are shown to include vidicons and a cathode ray tube, they also may comprise flying scanners well known in the art.

Present aerial photographs have a resolution of about 20 line pairs/mm or 1,600 resolution elements per square millimeter. A 320 X 320 resolution element raster at photo scale would thus be 8 mm square, 8 mm also being convenient for the subject invention with the optical system of the scanners being chosen appropriately to match the film to the pickup system.- Since the overlap or model area of the diapositives is approximately X 220 mm, i.e., 22,000 square mm total, it will be seen that the scanners will scan only a small portion of the overlap at any instant and that 22,000/64 or approximately 350 patches of raster size must be investigated to produce a complete orthophotograph of the model area.

Owing to the absence of adequate transformation means in prior art systems for adjusting the scan raster of the scanners, such orthophoto printers using the patch method of printing have been forced to employ a patch area of less than about 1 square mm in order to avoid visible discontinuities between adjacent patches. This small patch size has seriously restricted the speed of operation of such instruments. However, using the teachings of the present invention for image transformation, a patch size of greater than 8 mm square at photo scale is made possible, and hence a much higher speed of operation can be obtained than has been possible hitherto.

A preferred embodiment of the printer 43 is shown in more detail in FIGS. 2-4. The positioning mechanism of this device is described and claimed in more detail in my copending application entitled Photo Positioning Device, Ser. No. 44,305, filed June 8, 1970, now U.S. Pat. No. 3,687,547 which is also assigned to the assignee of the present invention.

A frame assembly 70 is adapted to hold the photographic film 43A, whose emulsion is to be exposed to the orthophotograph. The frame assembly 70 rests upon a flat base assembly which includes a plate 71 and is provided with a suitable surface to provide easy movement of the frame 70 acrossthe plate 71. Bearing feet or pads have been used on the underside of one frame assembly 70 and were found to work well. A pair of geared driving

racks

72 and 73 each carry at one end thereof a frame engaging end member 74, 75, respectively. Members 74 and 75 each carry a pair of rollers 76 which rotate about horizontal axes and ride on the upper surface of the plate 71. Second pairs of rollers 77 supported for rotation about a vertical axes and each of the members 74 and75 engage the

edges

102, 103 of the frame assembly 70. The outer ends of the

racks

72, 73 are supported by rollers 78. The

edges

102, 103 of the frame assembly 70 are'flat surfaces which intersect at an angle of 90 for the particular system illustrated herein. The racks 72=and 73 are maintained perpendicular to the

surfaces

102 and 103 and therefore the racks, if extended, would intersect at an angle of 90.

The frame 70 is maintained in engagement with each of the rollers 77 by any suitable assembly. In the preferred embodiment, the

opposite corners

79, 80 of the frame 70 have the ends of

cables

81 and 82 secured thereto. Cable 82 passes around a guide 83 supported on plate 71, and then around guide 84 also supported on plate 71. In a similar manner, the cable 81 passes around the guide 84. Two cables extend from guide 84 around a guide 85 supported for rotation about a horizontal support located in the plane of the plate 71, through an opening in the plate 71 adjacent guide 85, and around a pulley 86 having a weight 87 secured thereto. Through pulley 86, the cables extend through an opening, not illustrated, in plate 71, around an adjustment eccentric 88, and are secured by their respective ends to clamps 89 attached to the plate 71. The arrangement is such that the weight 87 acting through the

cables

81 and 82 provides a yielding force to the frame 70 which arches the

edges

102 and 103 into engagement with the rollers 77 associated with

drive racks

72 and 73. Rotation of the eccentric 88 is used for initial adjustment of the cables.

A drive gear 91 secured to the drive shaft of a reversible electric motor 463 engages the rack 72. In a similar manner, a drive gear 1 12 secured to the drive shaft of a second reversible electric motor 46A engages the drive rack 73. The operation of the reversible electric step motors 46A, 46B is interrupted by operation of an associated control switch by arms 93, 111 having

rollers

94 and 112 engaged with the non-toothed edge of the associated

racks

72 or 73. The arms 93 and 111 are pivoted on pins secured to the plate 71. The

switches

97 and 113 associated with the arms 93 and 111 are adapted to be operated whenever the respective arm is moved clockwise. The end members 74 and on the

racks

72 and 73 have beveled surfaces, such as surface 92 on member 74, which engage the

rollers

94 and 112 whenever the racks reach their maximum extent of outward movement. Therefore, the

associatedswitch

97 or 113 will be actuated to interrupt further drive of the rack. Corresponding beveled surfaces, such as surface 92A on rack 72, on the outer ends-of the

racks

72 and 73 serve the same purpose when the maximum extent of inward travel has been reached.

As seen in FIGS. 2 and 4, a lens 101 is aligned with the intersection of the lines of travel of

racks

72 and 73 so that the center of printing corresponds to this intersection. More specifically, this intersection occurs at the intersection of the pitch lines of the drive racks 72 and 73.

The film 43A can be held in position in the frame 70 by various means. For purposes of illustration, the film 43A is secured to a backing plate 70A. A corner stay 98 is shown as being in engagement with one corner of the plate 70A with springs 99, 100 urging the corner stay 98 and plate 70A towards the opposite corner of the frame 70.

Theorthphotograph is constructed by first establishing a pair of model coordinates within the computer 29, then delivering stage coordinate signals via lines 46X, 46Y to the motors 46B, 46A of the printer 43, so as to cause the frame 70, and therefore the film 43A, to assume a position with respect to the optical center lens 101 corresponding to the selected model coordinates. At this point in time, the cathode ray tube 59. is blanked by the inhibit signal appearing on line 56A. Subsequently, the computer causes the

scanners

25 and 26 to reduce the center-point X parallax to an acceptable level and causes the scanner transports to reduce the Y parallax to zero by movements in response to stage coordinate signals delivered on

lines

44X, 44Y, 45X, 45Y. Thereafter, the higher order X parallax is reduced to zero in response to signals from the correlator 49, and subsequent operation of the raster shapers 62 and 63.

When X parallax and other errors are eliminated, the inhibit signal is removedfrom line 56A and the video output of either

scanner

25 or 26, as determined by the left-right signal on line 55A, is coupled via line 55 to the cathode ray tube 59. Accordingly, the corrected video signal appears as an image 104 on the face of the scanner 59. This image 104 will be coupled through the lens 101 to expose a portion of the film 43A. After exposure iscomplete, the computer 29 selects new model coordinates and delivers appropriate stage coordinate signals via lines 46X, 46Y, so that the printer 43 assumes a new position. Thereafter, the cycle is repeated.

When the entire overlap area of the stereo photographs has been treated, the orthophotograph appears, as in FIG. 5, to comprise a plurality of adjacent, square patches 110.

If each of the patches reproduces its corresponding correlation zone with absolute fidelity, and if the patches 110 are precisely aligned with each other, the boundaries between patches would be practically indistinguishable. However, errors in alignment do occur,

despite the use of a precise and accurate plotting device such as illustrated in FIG. 2. The aforementioned difficulties of obtaining a uniform, non-distorted trace on a cathode ray tube contribute to distortions in position as well as light intensity at the extremities of each patch. Accordingly, the boundaries between adjacent patches often appear as a plurality of vertical and horizontal lines, 111, 112.

Although in most cases these lines are but mildly distracting, they become of significance when they coincide with an important feature of the orthophotograph. For example, the vertical line 111A in FIG. tends to obscure a portion of a runway 113 depicted therein. This distortion may materially lessen the value of the orthophotograph in cartographic applications, wherein very accurate detail is required.

Accordingly, the method of the invention allows construction of an orthophotograph by a hexagonal patch.

With reference now back to FIGS. 2-4, a plate 106 includes a plurality of apertures 107 for receiving a corresponding plurality of pins 105 which are secured in plate 71. Plate 106 also defines a centrally-located, hexagonal aperture 108 whose area corresponds to a desired area of each patch making up a composite orthophotograph. The plate 106 is generally positioned so as to align the center of aperture 108 with the center of optics 101. Therefore, the hex patch which is printed is centered on the image 104 reproduced by CRT 59.

To construct the orthophotograph, the model coordinates are selected by the computer 29 so that the frame 70 is first moved in uniform increments along the Y axis until the Y-dimension of the orthophotograph has been traversed. Then, the X model coordinate is moved by an appropriate increment, and the Y model coordinate is moved by an increment that is out of phase with the adjacent Y coordinate in a direction opposite to that previously traversed. Printing thereafter proceeds in uniform increments along the Y axis in the opposite direction until the Y-dimension is again traversed, at which time the cycle is repeated. The X and Y increments should be chosen in view of the dimensions of hexagonal aperture 8 so that adjacent patches are juxtaposed.

A resultant composite orthophotograph is seen to comprise, in FIG. 6, a plurality of adjacent, hexagonal patches 114. Although problems of patch misalignment may still occur, the tracing errors occurring at the edges of the image 104 are reduced due to the masking effect of plate 106. More important, misalignment and tracing error are much less apparent in the orthophotograph of FIG. 6, in that there are no continuous straight lines extending across the photograph for the observers eye to follow. In addition, important features of the overlap area are not obliterated, as might be in the case using a rectangular patch such as in FIG. 5.

Because inaccuracies may yet arise from CRT tracing error and from the difficulty of effecting a complete transformation over a given overlap area, the size of the hexagonal aperture 108 may be varied to allow more precision and accuracy in the composite orthophotograph. Accordingly, a number of plates 106 may be provided, each having a different-sized hexagonal aperture 108. As the aperture size is changed, the programmed model coordinates in the computer 29 must also be changed to assure accurate spacing of the patches 114.

While this invention has been described with reference to a preferred embodiment thereof, it is to be clearly understood by those skilled in the art that the invention is not limited thereto, but rather is intended to be bounded only by the limits of the appended claims.

What is claimed is:

1. A method for printing an orthophotograph from the overlap area of a pair of stero photographs onto a sensitized film, comprising the steps of scanning a patch on each of said pair of stereo photographs about a point established by a predetermined set of model coordinates, each patch comprising a portion of said overlap area representing homologous areas of said pair of stereo photographs, providing an image from said scanning which corresponds to said homologous areas and which is compensated for parallax and other distortion errors, masking the edges of said image to provide a hexagonal image, and exposing a portion of the sensitized film to said hexagonal image, further comprising the steps of repeatedly modifying said set of model coordinates by predetermined increments, and correspondingly adjusting said areas of scanning and the relative positions of said sensitized film and said hexagonal image so that adjacent patches of said pair of stereo photographs are successfully investigated and printed.

2. In an orthophoto printing system comprising in combination a photo positioning means for holding first and second photographs making up a stereo pair, a scanner means including first and second scanners aligned with said photographs and each including raster signal means for controlling scanning of a selected patch on each photograph, each patch being an area of a photograph covered in one complete scan cycle with the scan pattern for each scan cycle being a plurality of adjacent parallel scan lines, a printing means including a scanning display means and means holding a segment of sensitized film in alignment with said scanning display means, said scanning display means including means providing an image corresponding to the undisturbed scan pattern of one of said vidicons for the exposure of a patch of film made up of a plurality of adjacent lines, means connecting said scanning display means with said scanner means to render said scanning display means under the control of signal information derived from said scanner means, signal correlating means coupled with said scanner means and operative to derive error signals proportional to the timing differences between homologous components of the video signals provided by said first and second scanners, means connecting said correlating means to said raster signal means in response to said error signals to alter the scan pattern for at least one of said first and second scanners, and signal memory means connected between said correlating means and said raster signal means for storing the error signals derived from a complete area being scanned by said scanner means, said signal storage means providing output signals to control the alteration of the raster of at least said one of said scanners during the operation of said scanning display means with the image for said scanning display means remaining the same as an undisturbed scan pattern of one of said scanners, an improvement in said printing means comprising means defining a hexagonal aperture, said means being interposed between said scanning display means and said sensitized film for masking the edges of said image of said scanning display means, to reproduce on said sensitized film a hexagonal patch corresponding to a portion of said undisturbed scan pattern of one of said vidicons.

3. The improvement as recited in claim 2, further comprising means repeatedly moving said photographs and said sensitized film with respect to said scanner means and said scanning display means, respectively, in predetermined increments dependent in part on the size of said hexagonal aperture, said movements being effected after the completion of each raster alteration caused by said signal storage means.

4. The improvement as recited in claim 3, further comprising means blanking said scanning display means until the completion of each raster alteration caused by said signal storage means.

5. An automatic orthophoto printing system, comprising means for providing a video signal from a pair of stereo photographs which corresponds to patches thereof representing homologous areas in a portion of the total area of said stereo photographs and which is compensated for parallax and other visual distortion errors, a scanning display means for displaying an image corresponding to said video signal, means masking said image to produce a hexagonal image, means exposing a sensitized film to said hexagonal image, a photo positioning means for adjusting the relative position of said hexagonal image displayed on said scanning display means in said sensitized film, and further including means for repeatedly moving the centers of said patches and the relative positions of said sensitized film and hexagonal image in discrete increments to construct an orthophotograph.

6. A system as recited in claim 5, wherein said scanning display means comprises a cathode ray tube.

7. A system as recited in claim 5, wherein said scanning display means comprises a flying spot scanner.