US3883251A

US3883251A - Single photo epipolar scan instrument

Info

Publication number: US3883251A
Application number: US460637A
Authority: US
Inventors: Uuno V Helava
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1974-04-12
Filing date: 1974-04-12
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13
Also published as: CA1024898A; DE2515975A1; IT1037207B; JPS593685B2; GB1473017A; FR2267539B1; CH592867A5; JPS50142060A; DE2515975B2; FR2267539A1

Abstract

An instrument for scanning single photographs to generate and store image data along epipolar lines for subsequent processing and map making is disclosed. The instrument embodies an electronically controlled mechanical stage translating the photographic image relative to a stationary microdensitometer along epipolar lines and a storage unit for storing the image data generated by the microdensitometer. An alternate embodiment of the mechanical stage includes a rotary stage reducing the scanning along epipolar lines to a simple X or Y translation. Alternate embodiments of the microdensitometer includes linear arrays of detector elements permitting the scanning of adjacent lines parallel to the epipolar lines for removing Y parallax in the subsequent processing or for scanning a plurality of epipolar lines during a single X axis translation. The storage unit may store the image data in analog or digital form in accordance with the requirements of the associated processing equipment.

Description

United States Patent [1 1 Helava SINGLE PHOTO EPIPOLAR SCAN INSTRUMENT [75] Inventor: Uuno V. Helava, Southfield, Mich.

[73] Assignee: The Bendix Corporation, Southfield,

Mich.

[22] Filed: Apr. 12, 1974 [2]] Appl. No.: 460,637

UNITED STATES PATENTS 3,606.55] 9/l97l Becherer et al. 356/203 3,659.939 5/[972 Hobrough .a 250/558 X 3,741,664 6/l973 Torin 356/203 Primary Examiner-Palmer C. Demeo Attorney, Agent, or FirmJames R. Ignatowski [4 1 May 13, 1975 [57] ABSTRACT An instrument for scanning single photographs to generate and store image data along epipolar lines for subsequent processing and map making is disclosed. The instrument embodies an electronically controlled mechanical stage translating the photographic image relative to a stationary microdensitometer along epipolar lines and a storage unit for storing the image data generated by the microdensitometer. An alternate embodiment of the mechanical stage includes a rotary stage reducing the scanning along epipolar lines to a simple X or Y translation. Alternate embodiments of the microdensitometer includes linear arrays of detector elements permitting the scanning of adjacent lines parallel to the epipolar lines for removing Y parallax in the subsequent processing or for scanning a plurality of epipolar lines during a single X axis translation. The storage unit may store the image data in analog or digital form in accordance with the requirements of the associated processing equipment.

16 Claims, 7 Drawing Figures PATENTEU MAY I 31975 SHEET 2 OF 4 SINGLE PHOTO EPIPOLAR SCAN INSTRUMENT BACKGROUND OF THE INVENTION l. Field of the Invention Photogrammetry the science of making reliable measurements by the use of photographs, usually aerial photographs in surveying and map making.

2. Brief Description of the Prior Art The art of making maps from aerial photographs has made rapid progress over the past two decades, The art has developed from the hand measurement and hand computation stage to the present almost completely automatcd systems which are capable of matching conjugate image points, computing parallax data and drawing a variety oftypes of maps from a pair of stereo photographic images. The maps may range from a rela tively simple orthoprojection map which transposes the image detail ofthe photograph from its original projection, to an ortho-projection which both rectifies the image and corrects for perspective displacement, to complex contour maps giving elevation detail as well as rectification and correcting for perspective displacement. An early photogrammetric semi-automatic plottcr was disclosed by the instant inventor in US, Pat. No. 3.1 l6,555 in which conjugate image points on two stereophotographs were visually superimposed by the operator. In the context of this specification, conjugate image points are defined as identical image points on two different stereoscopic images. Electrical signals indicative of the displacement required to superimpose conjugate image points on two stereoscopic images along with other electrical signals were used to generate the desired map. Subsequently, electronic correlation methods for detecting conjugate image points from electro-optically derived signals generated by scanning the two stereoscopic images were developed. Typical electronic correlation methods are disclosed in US. Pat. No. 3,548,210 Automatic stereoplotter" W. E. Chapelle et al. This correlation may be performed in either the analog or digital domain. The advent of this correlation capability removed the human operator from the system making the stereoplotting instruments almost completely automatic. A further improvement to the automatic stereoplotter systems was the development of the epipolar line principle disclosed in US. Pat, No. 3,726.591 Stereoplotting Apparatus for Correlating Image points Disposed Along Epipolar Lines by U. V. Helava et al. The epipolar line principle significantly increased the ability to reliably scan conjugate imagery, reduced the complexity of the scanning pattern, and significantly reduced the complexity of the attendant scan and correlation apparatus.

The prior art has been almost exclusively directed to photogrammetric stereoplotters or stereomappers wherein the data from both stereoscopic images is si multaneously generated and the correlation of the data to determine conjugate imagery performed in real time. Although these automatic stereoplotter systems offer extremely favorable performance figures, the requirement for real time stereo operation makes them highly complex and very expensive.

In many practical map production tasks, such as the production of ortho-projection maps, it is possible to trade real time operation and the number of conjugate points processed for simplicity and lower costs. Therefore, the objective of the invention is a relatively simple single photo epipolar scan instrument for generating image data along epipolar lines by scanning only one photographic image at a time. This approach is possible because the epipolar scan principle permits reliable location of conjugate epipolar lines of imagery in a stereo pair, therefore, image coordinates of such epipolar lines can be readily determined and image scanning motions controlled accordingly eliminating the need for scanning both images simultaneously in real time.

SUMMARY OF THE INVENTION The disclosed scan instrument employs the epipolar scan principle which permits reliable location of conjugate epipolar lines of imagery on a pair of stereoscopic images, therefore, each photographic image of the stereoscopic pair may be scanned one at a time and the generated image data stored for subsequent processing and map making operations. The ability to scan and store the image data from each image separately with reliable retreival of conjugate imagery eliminates the requirement for simultaneously scanning both stereoscopic images, the requirement for on-line processing of the generated conjugate image data and the attendant complex and costly instrumentation.

The single photograph epipolar scan instrument com prises a base, a microdensitometer rigidly attached to the base detecting the image detail in a predetermined area in the photograph, a mechanical stage translating the photograph image relative to the microdensitometer, a control unit actuating the mechanical stage to translate the photographic image relative to the microdensitometer along epipolar lines and a storage unit storing the image data generated by the microdensitometer. The microdensitometer may scan one or more epipolar lines during each mechanical translation and may generate data along adjacent lines parallel to each epipolar line for the subsequent removal of Y parallax during the data processing.

The objective of the invention is to provide a simple scan instrument for generating image data along epipo lar lines and storing the data for subsequent data processing. Another objective of the invention is to generate image data along epipolar lines and adjacent parallel lines for the removal of residual Y parallax during the subsequent data processing. Another objective of the invention is an instrument capable of scanning a plurality of epipolar lines during each mechanical translation. These and other advantages of the invention will become apparent from the following discussion of the preferred and alternate embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective ofa preferred embodiment of the single photograph epipolar scan instrument;

FIG. 2 is a sketch illustrating the epipolar principle;

FIG. 3 is a perspective of an alternate embodiment of the single photograph epipolar scan instrument including a rotary stage;

FIG. 4 is an optical diagram illustrating the elements of the microdensitometer and integrated microscope;

FIG. 5 is an optical diagram illustrating the elements of an alternate embodiment of the microdensitometer having a linear array of detector elements;

FIG. 6 is an optical diagram illustrating the elements of an alternate embodiment of the microdensitometer capable of scanning a plurality of epipolar lines during each mechanical translation; and

FIG. 7 is a flow diagram showing the conversion of the generated analog signal to digital data for storage in a digital memory.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. I is a perspective view of a preferred embodiment of the disclosed single photo epipolar scan instrument. The scan instrument 10 comprises an X-Y measuring stage 12 mounted on a rigid base 14. The X-Y measuring stage 12 is comprised of a Y axis carriage 16 attached to and constrained to move parallel to the top surface 18 and base 14 in the Y direction and an X axis carriage 20 attached to the Y carriage l6 and constrained to move parallel to the top surface 18 of the base 14. The X and Y coordinates of the instrument are indicated by coordinate arrows 22 to the left of the instrument. The Y axis carriage 16 is supported along one edge by a rod 24 slidably inserted through a passage 26 formed along the one edge of the Y axis carriage 16. The rod 24 is supported at both ends by upstanding brackets 28 and 30 fixedly attached to the base 14. The other end of the Y axis carriage 16 is supported by a screw shaft 32 passing through a threaded passageway 34 formed along the other edge of the Y axis carriage 16. The ends of the screw shaft 32 are supported by

upstanding brackets

36 and 38 fixedly attached to the base 14. The rod 24 and screw shaft 32 are disposed parallel to the surface 18 of the base 14 and constrain the movement of the Y axis carriage to a movement in the Y direction parallel to the base. The ends of screw shaft 32 protrude beyond the

brackets

36 and 38 at each end respectively and are adapted to receive a Y handwheel 40 at one end and a Y axis servo drive 42 at the other end.

The X axis carriage is supported along one edge by a rod 44 slidably inserted through a passage 46 formed along the one edge of the X axis carriage 20. The rod 44 is supported at both ends by means of upstanding brackets 48 and 50 fixedly attached to the Y axis carriage 16. The other end of the X axis carriage 20 is supported by a screw shaft 52 passing through a threaded passageway 54 formed along the other edge of the X axis carriage 20. The ends of the screw shaft 52 are supported by upstanding brackets 56 and 58 fixedly attached to the Y axis carriage 16. The rod 44 and screw shaft 58 are disposed parallel to the surface 18 of the base 14 and constrain the movement of the X axis carriage to a movement in the X direction parallel to the base. The ends of screw shaft 52 protrude beyond the brackets 56 and 58 at each end respectively and are adapted to receive an X handwheel 60 at one end and an X axis servo drive 62 at the other end.

The Y axis carriage 16 may be moved along the Y axis in either direction by manually cranking the handwheel 40 or by electrically actuating Y axis servo drive 42. Because the X axis carriage 20 is attached to the Y axis carriage as previously described, mechanical movement of the Y axis carriage 16 in the Y direction correspondingly moves the X axis carriage 20 in the Y direction an equal amount. The X axis carriage 20 may be moved along the X axis in either direction by manually cranking the handwheel 60 or electrically actuating X axis servo drive 62. The X axis movement of the X axis carriage 20 is independent of the movement of the Y axis carriage 16.

The photographic image 64 to be scanned is fixedly attached to the X axis carriage by any conventional mounting means and is constrained to move therewith. The coordinated movement of the X axis carriage 20 and Y axis carriage 16 along the Y axis and the independent movement of the X axis carriage 20 along the X axis permit the photographic image 64 to be independently scanned along either axis independently or with one coordinated movement.

Although the X-Y stage 12 in the preferred embodiment is illustrated as using guide rods and screw shafts for constraining and driving the individual carriages along the X and Y axis respectively, it is well known in the art that other forms of X-Y carriages such as dove tail" or vee" carriages may be equally used. The manner in which the motion of the carriages are constrained and driven are immaterial to the invention.

The image detail on the photographic image 64 is converted to electrical signals by a microdensitometer 200 comprising an input 202 and a detector 204, the details of which are illustrated in FIGS. 4, 5, and 6. FIGS. 4, S and 6 show alternate embodiments of the densitometer capable of generating data along a plurality of lines during each X axis scan. The input 202 is fixedly attached to the base 14 and illuminates a predetermined area on the photographic image 64 from below. The incident light is modulated by the image detail on the photographic image 64 in the illuminated area. The detector 204 is fixedly disposed above the photographic image 64 to receive the light from the input modulated by the photographic image and generates electrical signals indicative of the image detail being illuminated. The detector 200 is rigidly supported above the photographic image 64 in optical alignment with the input optics by an angle support bracket 66, fixedly attached to base 14. The illuminated area may be a single point, a series of points, or a line image of a predetermined length as shall be discussed later with reference to FIGS. 4, 5, and 6.

For convenience of aligning the densitometer with selected points on the photographic image 64, the scan instrument 10 further includes a low power microscope system 300 integrated with the input 202 and the detector 204. The details of the low power microscope 300 are illustrated in FIG. 4 and will be discussed relative thereto.

The single photo epipolar scan instrument further includes a scan control unit 68 generating epipolar scan signals actuating the Y axis servo drive 42 and the X axis servo drive 62 to translate the photographic image 64 relative to the microdensitometer so that the area illuminated by the microdensitometer scans along epipolar lines on the photographic image. The scan control unit 68 generates the control signals on the basis of external information supplied to it in a suitable form. The form of the external information may be supplied from prepared programs, such as a punched tape, punched cards, or magnetic tape similar to any of the well known numerical control devices designed for driving machine tools. In a more sophisticated form, the scan control unit 68 would embody special purpose logic, such as a minicomputer, as is also common in numerical control machines for computing the required motion of the photographic image 64 which will cause the microdensitometer to scan along epipolar lines. It could then perform more complex tasks; for example, the external information may be less complete and the mini-computer would perform interpolation and even geometric computations, as done in existing stereomappers to obtain final data for driving the X-Y stage. The mini-computer would also be able to control and drive the memory unit 70.

Electronic logic circuitry for generating electric signals for the X and Y axes servo drives to scan along the epipolar lines when the pattern is known and drive signals for the memory unit 70 is well within the capability of the existing art and does not need to be discussed in detail.

The electrical signals indicative of the imagery scanned on the photographic image 64 along the individual epipolar lines is stored in a memory unit 70 for subsequent data manipulation. The electrical signals may be stored in an analog storage or the electrical signals may be converted to digital data and stored in a digital memory. The latter method offers several advantages which are obvious to those skilled in the art. Any digital storage means may be used, but magnetic tape or magnetic discs appear particularly suitable. Such memories may be used in conjunction with commercial general-purpose computers for efficient offline correlation and other processing. It is recognized special-purpose computers and auxiliary processors may also be used if deemed advantageous.

The operation of the single photo epipolar scan instrument is as follows: A photographic image for which the parameters of the epipolar scan pattern are known is mounted on the X axis carriage between the input 202 and detector 204 of the microdensitometer as shown in FIG. 1. With the aid of the low power microscope 300 the area illuminated by the densitometer is aligned with predetermined image points on the photographic image 64 by manually cranking X axis handwheel 60 and Y axis handwheel 40. The scan control unit 68 is then activated and generates scan control signals in accordance with the parameters of the epipolar line scan patterns inserted into the scan control unit 68. The scan control signals actuate the X axis servo drive 62 and the Y axis servo drive 42 to move the photographic image 64 across the area illuminated by the microdensitometer along the desired epipolar lines. The electrical signals generated by the microdensitometer are then stored in the memory unit 70 in either analog or digital form as the case may be.

After the first photographic image has been scanned and the data stored in the memory unit 70, the first photographic image is then removed from the X axis carriage and replaced with a second photographic image 64' which is the other photographic image of a stereoscopic pair. The same procedure is followed with the second photographic image 64' and the image data from the second photographic image is also stored in the memory unit 70. It would be obvious to a person skilled in the art that in many practical map making tasks. the storage of the data from the second photographic image may not be necessary ifthe required subsequent data processing can be performed in real time with the generation of the data from the second image. Under these circumstances, the data from the second image could be input directly into the processor and the conjugate data from the first image extracted from the memory unit 70 as required.

FIG. 2 is presented to better understand the epipolar line principle disclosed in the Helava et al. patent and used in the single photo epipolar scan instrument. Two

stereoscopic

photographic images

102 and 104 of a scene or land mass 106 taken from

different vantage points

108 and 110 at different elevations are shown. Corresponding epipolar lines 112 and 114 on

stereo images

102 and 104 are defined by an epipolar plane 116 which intersects the two photographic images. Epipolar plane 116 is defined by the

vantage points

108 and 110 and by one point 118 on the land mass 106. Different epipolar lines on

photographic images

102 and 104 such as

lines

120 and 122 can be generated by rotating epipolar plane 116 about the line connecting

vantage points

108 and 110 to the position designated as 124. The epipolar lines on stereo image 102 are straight lines that define a fan pattern radially emanating from point 126 lying in the plane of image 102. Point 124 is determined by the intersection of the projection of a line connecting

vantage points

108 and 110 with the plane of image 102. Similarly, the other epipolar lines on stereo image 104 comprises straight lines radially emanating from a point 128. Point 128 is a point in the plane of stereo image 104 where the projection of the line connecting

vantage points

108 and 110 intersects the plane of stereo image 104. The epipolar principle has the advantage that conjugate imagery on the two photographic images lie along conjugate lines which permits reliable location of conjugate imagery in a photographic stereo pair of images.

An alternate embodiment of the single photo epipolar scan instrument 10 is shown in FIG. 3. The alternate embodiment includes a rotational stage to simplify scanning of the fan pattern formed by the epipolar lines. The elements of FIG. 3 having counterparts in FIG. I have the same numerical indicia to avoid confusion. In addition to the base 14 and X-Y stage 12, the alternate embodiment includes rotational carriage 72. The rotational stage 72 comprises a base 74 having a circular aperture 76 adapted to rotatably receive rotary member 78 mounted to X axis carriage 20. A ring bearing (not shown) or other bearing member may be interposed between the base 74 and the rotary member 78 to permit the rotary member 78 to freely rotate within aperture 76 with insignificant lateral or horizontal movement. The periphery of the rotary member 78 has a plurality of teeth adapted to engage a worm gear 82 coaxially attached to shaft 84 and adapted to rotate therewith. Shaft 84 is rotatably supported at both ends by upstanding brackets 86 and 88 fixedly attached to base 74. The opposite ends of shaft 84 protrude through the brackets 86 and 88 and are adapted to receive angle handwheel at one end and angle servo drive 92 at the opposite end. Rotation of shaft 84 by either cranking handwheel 90 or electrically actuating servo drive 92 rotates the worm gear 83 which engages teeth 80 and rotates the rotary member 78. The photographic image 64 is mounted on the rotary member 78 and rotates therewith. In the embodiment of FIG. 3, the scan control unit 68 also generates control signals controlling the rotation of the rotatable stage 72.

The operation of the alternate embodiment is similar to the operation of the preferred embodiment of FIG. 1. However because of the addition of the rotary stage, the scan signals generated by the scan control unit have been simplified. The photographic image 64 is mounted on the rotary stage 78 as shown and oriented by viewing through the microscope 300 and cranking

handwheels

40, 60 and 90 as before. Instead of the scan control unit generating coordinated control signals for the X-Y stage to produce a composite motion of both stages to follow an epipolar line, the image is rotated by an appropriate signal to the rotary stage so that the epipolar line being scanned lies along the X axis, and the scanning of each epipolar line is a simple X axis translation. Each time the photograph is moved in the Y direction to the next sequential epipolar line, the ro tational stage is indexed so that the next sequential line is also along the X axis.

The details of densitometer 200 are illustrated in FIG. 4. The input optics 202 comprise a light source illustrated as a lamp 206 illuminating a pinhole aperture 208 in an opaque baffle 210 by means of a collector lens 212. The light from the lamp 206 passing through the pinhole aperture is focused at a point 214 on the photographic image 64 by a focusing lens 216.

The detector 204 comprises a collector lens 218 collecting the light incident at point 214 and modulated by the image detail on photographic image 64 and focuses the collected light on a detector 220. The detector 220 generates an electrical signal indicative of the intensity of the light received,

The low power microscope 300 is integrated with the densitometer optics as illustrated. The microscope comprises a light source indicated as lamp 302 illuminating the area around point 214 by means of beam splitter 304 and collector lens 218. The lamp 302 is disposed from the collector lens 218 a distance approximately equal to the focal length ofthe collector lens so that the photographic image 64 is illuminated with essentially parallel light. The parallel light passes through the photographic image 64 and is partially reflected by beam splitter 306 to the objective lens 308 of the mi croscope, The objective lens forms an aerial image 310 of the illuminated portion of the photographic image which is relayed to the microscope eyepiece 312 by means of relay lens 314. Deflection optics 316 such as a mirror or prism may be incorporated in the microscope to place the eyepiece 312 in a convenient position for the operator 318. It is recognized that appropriate housing and optical baffling (not shown) will be provided as is customary in optical instrument design.

An alternate embodiment of the microdensitometer capable of scanning a plurality of lines during each X axis epipolar scan is shown in HO 5. In the embodiment of PK). a light source 206 illuminates a narrow slit aperture 222 in an opaque baffle 224 by means of collector lens 226. The slit aperture 222 is disposed generally perpendicular to the X axis of the instrument. in the illustrated embodiment, the X axis is disposed normal to the plane of the drawing and passes through the centerline 228 ofthe illustrated optical system. The light passing through slip aperture 222 is focused on the photographic image 64 by means of lens 230. The length of the slit image on the photographic image 64 is sufficient to encompass image points designated as

points

232, 234 and 236 respectively. The light forming the slit image passes through the photographic image 64 and is modulated by the image detail on the photographic image. The modulated slit image on the photographic image 64 is focused on three

detectors

238, 240 and 242 disposed parallel to the slit aperture de tecting the modulated light emanating from

points

232, 234 and 236 respectively. The

points

232, 234 and 236 may be defined by the natural apertures of the detectors or may be defined by a series of pinholes (not shown) disposed in front of the detectors. Although the illustrated embodiment shows three separate detectors, the individual detectors may be embodied in a single integrated device such a linear array of charge cou pled devices, a linear array of bucket brigade devices, a linear array of channel electron multipliers having individual outputs for each channel electron multiplier, or other linear arrays of photodetectors. The elements of the microscope 300 are omitted from FIG. 5 to simplify the illustration.

During a single X scan of the photographic image, the image detail along the desired epipolar line defined by point 234 is detected by detector 240.

Detectors

238 and 242 detect the image detail on the photographic image 64 along lines parallel to the desired epipolar line a short distance in the Y direction on either side thereof. Because the lines are close together, the fan effect of the epipolar lines is negligible. Further during the subsequent processing of the data, the data of a neighboring line may be used to eliminate residual Y parallax that may occur due to other extraneous factors. Of course it should be recognized that more than the three illustrated detectors may be used permitting the generation of data along more than three parallel lines if desired. The three illustrated detectors are used I to only illustrate the principle and not limit the scope of the invention.

A still further embodiment of the microdensitometer 200 is illustrated in FIG. 5 having the capability of scanning a plurality of epipolar lines during a single X axis scan of the photographic image. The input optical system 202 is the same as that disclosed with reference to FIG. 4 and comprises light source 206, slit aperture 222 in an opaque baffle 224, collector lens 226 and lens 230 illuminating a line area on the photographic image 64 parallel to the Y axis. The line area on the photographic image 64 is of a sufficient length to include a plurality of epipolar lines. In the illustrated embodiment, three individual epipolar lines are indicated by

points

246, 248 and 250. in place of the fixed focal length lens 244 illustrated in FIG. Sis a variable magnification zoom lens 252 mechanically actuated by a servo drive 254 receiving signals from the scan control unit 68 which are indicative of the X position of the photographic image 64. The zoom lens focuses image points 246, 248 and 250 on discrete detector elements of a linear array of photodetectors 256. Again the detector may be a plurality of discrete detectors such as shown on FIG. 5 or may be an integrated array of linear detectors such as charge coupled devices, bucket brigade devices, or other types of array detectors having temporary storage and sequential readout capabilities known in the art, it being sufficient that the detector array 256 have at least one discrete detector element for each epipoiar line being scanned.

In a practical application an integrated linear array such as array 56 may have over [000 individual detector elements which may be readout in a serial or sequential fashion. This, however, is not a serious limitation since this serial readout with existing devices such as charged, coupled, or bucket brigade devices can be accomplished in approximately one microsecond. A more serious limitation is the fact that the sensors are integrating devices which require a predeterminable input (light level X integrated time) to achieve a satisfactory signal to noise level. Secondly, the motion of the X axis carriage will produce an undesirable smearing effect since the photograph is being moved during the integration time. Smearing can be controlled by gating the array but this is done at the expense of the integration time. This problem may be overcome by replacing the light source 26 with a high power gas discharge lamp producing 60 to I short duration high energy flashes per second. These flashes are short enough to freeze" the motion yet produce enough energy in each pulse to give good signal to noise ratios. The control unit 68 in this configuration includes additional circuitry to alternately generate the trigger signals for the discharge lamp and the readout signals for the integrated linear array.

The density data flow from a linear array having a large number of detector elements is very highv In fact the data flow is so high that the digital storage requirements can only be performed by very expensive state of the art computers. However. a low cost compromise is readily available. Instead of storing all of the data generated by the detector elements, the data from only selected detectors indicative of the desired epipolar lines need be stored. The selection control can be implemented by the control unit 68 associated with the scanner. By the selection process the requirement for the expensive memory may be eliminated.

The operation of the embodiment illustrated in FIG. 6 is as follows. With the photographic image displaced at one extreme of an X axis scan, the zoom lens is adjusted so that the desired epipolar lines are focused on the desired detector elements in the detector array. As the photographic image 64 is scanned along the X axis, the magnification of the zoom lens 252 is continuously changed by the servo drive 254 receiving signals from the scan control unit 68 indicative of the X axis position. The coordinated ehange in magnification of the zoom lens 252 with the X axis displacement of the photographic image 64 cause the individual detector elements of detector array 256 to detect imagery on the photographic image along convergent or divergent lines dependent upon the direction of the X axis scan and the direction of change in the magnification of the zoom lens 252. It is well within the purview of existing electronic and associated electro-optical elements to cause the individual elements in the detector array 256 to generate image data along epipolar lines, thereby permitting the plurality of epipolar lines to be scanned simultaneously during a single scan along the X axis.

When the memory unit 70 is an analog storage device. the analog signals from each detector element is input directly into the storage device along with a signal indicative of the scan position from the scan control unit. However if the detector is an integrated linear array and the light source is pulsed, the scan control unit 68 may sequentially generate trigger signals and readout signals at predetermined intervals, indicative of a predetermined distance along the X axis. The trigger signals on line 258 are applied to the light source 26 and the readout signals on line 260 are applied to the detector array 256 as previously discussed.

The signals from the individual elements are then input to the memory unit 70 where the signals from predetermined elements are selected and combined with appropriate digital addresses generated by the control unit 68 then stored in a predetermined order. The digital address signals are transmitted along line 262 from the control unit 68 to the memory unit 70.

It is obvious that the scanning of a plurality of lines of both sides of each epipolar line scanned to remove residual parallax transverse to the epipolar lines as discussed with reference to FIG. 5 may be accomplished with the embodiment illustrated in FIG. 6. These are shown as the lines 246', 248' and 250' emanating from both sides of the epipolar lines indicated by the

points

246, 248 and 250. However in the embodiment of FIG. 6, the alternate lines 246', 248' and 250' scanned will not be parallel to the epipolar lines scanned but will possess the fan pattern of the epipolar lines. The em bodiment of FIG. 6 is also not limited to scanning along three epipolar lines as illustrated but may scan a plural ity of epipolar lines during each X axis scan.

The memory unit shown in FIG. 1 may be either an analog or digital storage device, however. it is preferred that it be a digital storage. The generation of digital data from linear arrays of charge coupled devices or bucket brigade devices may be accomplished as discussed with reference to FIG. 6. However, analog data from analog detectors may be converted to digital data using any of the methods well known in the art. FIG. 7 illustrates one way this may be accomplished. The photographic image 64 is mechanically scanned along the X axis by the servo drive 62 in response to signals received from the scan control unit 68. As the photographic image moves relative to the microdensitometer consisting of input 202 and detector 204, the detector generates an analog electrical signal indicative of the imagery on the photographic image being scanned. The analog signals are amplified by amplifier 402 and the amplified signals are input to an analog to digital converter 404. Concurrent with the generation of the drive signals for the servo drive 62, the scan control unit generates sample signals at predetermined intervals indicative ofa predetermined distance of movement of image 64 along the axis. The sample signals are communi cated to analog to digital converter 404 along line 406 where they sample the analog signals at the predetermined intervals. The samples of the analog signals are then digitized using known techniques, then sequentially placed in a storage interface 408 such as a shift register were the digitized samples are temporarily stored until the scan is completed. At the completion of the scan, the scan control unit 68 generates a command signal on line 410 which empties as a block of digital data having an appropriate address as is common practice in the art. Electronic circuits to perform the above operations are well known in the art and need not be discussed in detail.

The single photo epipolar scan instrument has been described with reference to a preferred embodiment and alternate embodiments. Further, several alternate embodiments of the microdensitometer have also been described which show some but not all of the possible variations of the instrument. It is recognized that there are alternate ways that many of the functions may be performed or signals generated to achieve the stated objective of the invention, which are far to numerous to be discussed. The illustrated and discussed embodiments are only used to explain the invention and are not intended to limit the scope thereof.

What is claimed is:

l. A scan instrument for generating image data from a single photographic image along epipolar lines and storing the image data for subsequent data processing and map making comprising:

a rigid base;

stage means attached to said base for providing translatory motion along at least two mutually perpendicular axes relative to said base, said stage means adapted to receive said photographic image and translate said image along said mutually perpendicular axes;

microdensitometer means fixedly attached to said base for detecting the image details within a predetermined area on the photographic image and gen crating electrical signals indicative of the detected image details; I

control means for actuating said stage means to translate said photographic image relative to said densitometer causing said microdensitometer means to generate electrical signals indicative of the image details along a predetermined set of epipolar lines on the photographic image; and

means for storing the electrical signals generated by said microdensitometer means.

2. The scan instrument of claim 1 further including a microscope fixedly attached to said base for visually observing a portion of the photographic image in the immediate vicinity of the predetermined area being de tected by said microdensitometer to permit alignment of the photographic image with reference to the area detected by the microdensitometerr 3. The scan instrument of claim 2 wherein said stage means comprises:

a first stage, attached to said base and adapted to translate along one of said mutually perpendicular axes;

a second stage attached to said first stage and adapted to translate along the other of said mutually perpendicular axes, said second stage further adapted to receive and hold the photographic image;

and wherein said control means coordinately controls the translation of said first stage along said one axis and said second stage along said other axis to move the photographic image along each epipolar line in said set relative to the predetermined area being detected by said microdensitometer in a predetermined sequence.

4. The scan instrument of claim 3 wherein the epipolar scan pattern for the photographic image has been predetermined and a program coordinating the translation of said first and second stages for each epipolar line prepared, said control means is a program reader means actuating said first and second stages in accordance with said prepared program.

5. The scan instrument of claim 3 wherein the geometrical parameters of the photographic image are known, said control means includes means for inserting said geometrical parameter into said control means and logic circuitry for computing from the known geometrical parameters the coordinate translation of said first and second stages required to scan the photographic image along the desired set of epipolar lines relative to the predetermined area being detected by the microdensitometer.

6. The scan instrument of claim 3 wherein said stage means further includes a rotary stage attached to said second stage and adapted to rotate the photographic image in a plane parallel to said mutually perpendicular axes, and said control means further includes means for actuating said rotary stage to rotate said photographic image to align the epipolar lines along one of said mu tually perpendicular axes whereby the scan of each epipolar line by the microdensitometer is reduced to a line scan along the mutually perpendicular axis aligned with the epipolar line.

7. The scan instrument of claim 6 wherein the epipolar scan pattern for the photographic image has been predetermined and a program coordinating the translation of said first, second, and rotary stages for each epipolar line prepared, said control means is a program reader means actuating said first, second and rotary stages in accordance with said prepared program.

8. The scan instrument of claim 6 wherein the geometrical parameters of the photographic image are known, said control means includes means for inserting into said control means the geometrical parameters and logic circuitry for computing from the known geometrical parameter the coordinate translation and rotation of the first, second and rotary stage respectively to scan the photographic image along the desired set of epipolar lines relative to the predetermined area being detected by said microdensitometer.

9. The scan instrument of claim 3 wherein said mi crodensitometer comprises:

input means rigidly attached to said base and disposed on one side of said photographic image for illuminating with light said predetermined area on the photographic image; and

detector means rigidly attached to the base and disposed on the other side of said photographic image for detecting the light modulated by the image detail in said predetermined area and for generating electrical signals indicative of the intensity of detected light.

10. The scan instrument of claim 9 wherein said means for illuminating illuminates a point on the photographic image and said means for detecting detects the light modulated by the image detail on the photographic image at said point 11. The scan instrument of claim 9 wherein said input means for illuminating illuminates the photograph with the image of a narrow slit of light, said slit of light disposed transverse to one of said mutually perpendicular axes and wherein said means for detecting comprises a linear array of detector elements disposed parallel to said slit of light, one of said detector elements disposed to receive the light transmitted through the photographic image from a small portion of the slit image during the scan translation transverse to the slit image, said small portion being indicative of said epipolar line and the other detector elements of said linear detector disposed to receive other portions of the slit image transmitted by the photographic image, said other portions defining lines displaced a predetermined distance from said epipolar line and parallel thereto, thereby providing image data along the epipolar line and lines disposed both sides of and parallel to the epipolar lines for the removal of residual parallax during subsequent data processing.

12. The scan instrument of claim 11 wherein said linear array of detector elements is an integrated array of detector elements having storage and sequential readout capabilities, said input means includes discharge lamp producing short pulses of high intensity light in response to a trigger signal and said scan control means further includes means for sequentially generating trigger signals to trigger said discharge lamp and readout signals to sequentially readout said integrated array at predetermined intervals indicative of a predetermined translation of the photograph along the mutually perpendicular axis transverse to said epipolar lines.

13. The scan instrument of claim 9 wherein said input means illuminates the photographic image with the image of a narrow slit of light, said slit of light disposed transverse to one of said mutually perpendicular axes, said detector means comprises:

a linear array of detector elements disposed parallel to the slit of light;

a zoom lens having a variable magnification disposed between said photographic image and said linear array of detector elements for focusing the light transmitted by the photographic image across the detector elements;

and wherein said control means further includes means for actuating the zoom lens to change the magnification of the slit image focused across the detector elements as a function of the mechanical translation along said axes transverse to said slit area to cause the detector elements to detect imagery along a plurality of epipolar lines during each mechanical translation along said axis transverse to said slit image.

14. The scan instrument of claim 13 wherein said linear array of detector elements is an integrated array of detector elements having temporary storage and sequential readout capabilities, said input means includes a discharge lamp producing short pulses of high intensity light in response to a trigger signal, and said control means further includes means for sequentially generating trigger signals to trigger said discharge lamp and readout signals to sequentially readout said integrated array at predetermined intervals indicative of a predetermined translation of the photographic image along the mutually perpendicular axis transverse to said epipolar lines.

15. The scan instrument of claim 2 wherein said storage means is an analog storage means.

16. The scan instrument of claim 2 wherein said storage means is a digital storage, said digital storage means further including means for converting the electrical signals generated by the microdensitometer into digital data.

Claims

1. A scan instrument for generating image data from a single photographic image along epipolar lines and storing the image data for subsequent data processing and map making comprising: a rigid base; stage means attached to said base for providing translatory motion along at least two mutually perpendicular axes relative to said base, said stage means adapted to receive said photographic image and translate said image along said mutually perpendicular axes; microdensitometer means fixedly attached to said base for detecting the image details within a predetermined area on the photographic image and generating electrical signals indicative of the detected image details; control means for actuating said stage means to translate said photographic image relative to said densitometer causing said microdensitometer means to generate electrical signals indicative of the image details along a predetermined set of epipolar lines on the photographic image; and means for storing the electrical signals generated by said microdensitometer means.

2. The scan instrument of claim 1 further including a microscope fixedly attached to said base for visually observing a portion of the photographic image in the immediate vicinity of the predetermined area being detected by said microdensitometer to permit alignment of the photographic image with reference to the area detected by the microdensitometer.

3. The scan instrument of claim 2 wherein said stage means comprises: a first stage, attached to said base and adapted to translate along one of said mutually perpendicular axes; a second stage attached to said first stage and adapted to translate along the other of said mutually perpendicular axes, said second stage further adapted to receive and hold the photographic image; and wherein said control means coordinately controls the translation of said first stage along said one axis and said second stage along said other axis to move the photographic image along each epipolar line in said set relative to the predetermined area being detected by said microdensitometer in a predetermined sequence.

6. The scan instrument of claim 3 wherein said stage means further includes a rotary stage attached to said second stage and adapted to rotate the photographic image in a plane parallel to said mutually perpendicular axes, and said control means further includes means for actuating said rotary stage to rotate said photographic image to align the epipolar lines along one of said mutually perpendicular axes whereby the scan of each epipolar line by the microdensitometer is reduced to a line scan along the mutually perpendicular axis aligned with the epipolar line.

9. The scan instrument of claim 3 wherein said microdensitometer comprises: input means rigidly attached to said base and disposed on one side of said photographic image for illuminating with light said predetermined area on the photographic image; and detector means rigidly attached to the base and disposed on the other side of said photographic image for detecting the light modulated by the image detail in said predetermined area and for generating electrical signals indicative of the intensity of detected light.

10. The scan instrument of claim 9 wherein said means for illuminating illuminates a point on the photographic image and said means for detecting detects the light modulated by the image detail on the photographic image at said point.

11. The scan instrument of claim 9 wherein said input means for illuminating illuminates the photograph with the image of a narrow slit of light, said slit of light disposed transverse to one of said mutually perpendicular axes and wherein said means for detecting comprises a linear array of detector elements disposed parallel to said slit of light, one of said detector elements disposed to receive the light transmitted through the photographic image from a small portion of the slit image during the scan translation transverse to the slit image, said small portion being indicative of said epipolar line and the other detector elements of said linear detector disposed to receive other portions of the slit image transmitted by the photographic image, said other portions defining lines displaced a predetermined distance from said epipolar line and parallel thereto, thereby providing image data along the epipolar line and lines disposed both sides of and parallel to the epipolar lines for the removal of residual parallax during subsequent data processing.

13. The scan instrument of claim 9 wherein said input means illuminates the photographic image with the image of a narrow slit of light, said slit of light disposed transverse to one of said mutually perpendicular axes, said detector means comprises: a linear array of detector elements disposed parallel to the slit of light; a zoom lens having a variable magnification disposed between said photographic image and said linear array of detector elements for focusing the light transmitted by the photographic image across the detector elements; and wherein said control means further includes means for actuating the zoom lens to change the magnification of the slit image focused across the detector elements as a function of the mechanical translation along said axes transverse to said slit area to cause the detector elementS to detect imagery along a plurality of epipolar lines during each mechanical translation along said axis transverse to said slit image.