Reseau apparatus for photogrammetry devices

A mensuration apparatus for converting film images and paper drawings into digital photogrammetric arrays to be computer processed, displayed, mensurated and analyzed. This mensuration apparatus includes a table on which a translatable camera and a reseau assembly are mounted. The reseau assembly includes an object mounting plate for mounting an object such as a photograph, map, or the like, and a grid mark system for superimposing grid marks on the object. The translatable camera includes a solid state camera having a two-dimensional array of light sensor elements mounted over the reseau assembly in a translatable mounting apparatus. Said translation camera can be moved as any desired position over the reseau assembly, as well as toward and away from the reseau assembly, forming three coordinate systems, which are correlated together for precise mensuration of an object image digitized by the solid state camera.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to digital photogrammetric apparatus and more 
specifically to a reseau grid for photogrammetric mensuration apparatus 
that can be effectively invisible and does and does not block or distort 
photogrammetric images. 
2. Background of the Invention: 
The photographic art for aerial surveillance, geological and archaeological 
study, mechanical, industrial, and architectural design and analysis, and 
other uses has become very well-developed over the past several decades so 
that sharp, clear photographic images of the earth's surface and of 
objects on the earth's surface are obtainable from aerial photography, 
satellite photography, and the like. In fact, there already are in 
existence virtually countless aerial photographs in files of national, 
state, and local government agencies, corporations, and individuals for 
purposes ranging widely from such things as military reconnaissance, 
surveillance and measurement of agricultural land and crop conditions, 
monitoring municipal development and growth patterns, map making, geologic 
assaying, land management, and the like. Additional photographing and 
re-photographing for subsequent comparison with previous conditions are 
being done on an increasing basis. 
For many purposes, however, analysis of such photographic images cannot be 
done by visual observation with sufficient accuracy or efficiency. For 
example, in spite of having exceptionally clear aerial photographic images 
available, it may be quite impossible, even with accurate graphic 
instruments and a magnifying glass, to measure the wing-span of an 
airplane parked on an airport apron, the square feet of pavement on all of 
the streets in a city, or the areas of potholes in a wetlands inventory of 
a prairie. 
Therefore, to improve their accuracy and efficiency, persons skilled in the 
art of photogrammetry have found that computers can be a very useful tool 
for enhancing the photographic images or parts of the images and to 
augment the analysis. To do so, the photographic image is converted into a 
digital format that can be stored, processed, and displayed on a computer 
controller graphic display output, such as a cathode ray tube (CRT), hard 
copy printer, plotter, or the like. 
A common method of converting a hard copy image to a digital array is to 
use a point sensor, such as a charge-coupled device (CCD), charge 
injection device (CID), or photodiode to scan the surface of the hard copy 
and measure the light either transmitted through, or reflected from, 
various points on the hard copy. The hard copy in this kind of process is 
usually mounted on a rotating drum or on a flat table that is movable in 
orthogonal X-Y directions. A large pixel array, such as a 20,000 by 20,000 
pixel area, can be acquired, which may, for example, be the pixel array 
needed to represent the information on a 9".times.9" (23 cm .times.23 cm) 
film image, assuming individual pixels of about 12.5 .mu.m diameter. 
Some systems use a linear detector or sensor array, instead of a single 
point sensor for the digital data acquisition. In such linear systems a 
large number (e.g., 1750) of individual light sensitive elements are 
grouped together in a linear row, and this linear array or row of sensors 
is used to sweep scan a path over the surface of the hard copy. 
Precise mechanical motion control is required for both the individual scan 
lines of a single point sensor and the groups of scan lines or sweep path 
of linear arrayed sensors in order to obtain a meaningful and useable 
pixel array of the photogrammetric image. Such mechanical accuracy, while 
necessary for accurate pixel designation and resolution, cannot be 
obtained economically in the degree that would be required for resolution 
commensurate to pixel sizes of less than, for example, 50 microns. Also, 
typical operations problems with such systems usually result from 
inability to achieve and maintain the mechanical accuracy needed over long 
periods of time. Consequently, the large data arrays required and the high 
cost to obtain the necessary mechanical accuracy have kept the use of 
digital image processing and photographic images in laboratories only and 
away from general commercial application and use. 
In recent years, several manufacturers have made available semiconductor 
chips on which a plurality of CCD's or CID's are arranged in a 
two-dimensional, rectangular array and mounted in a solid state camera, 
such as a "TM-540", manufactured by Pulnix, of Sunnyvale, CA. These solid 
state cameras with rectangular sensor arrays can detect and measure light 
from a fixed frame or rectangular portion of the image that a person 
desires to digitize for computer use. When such cameras are used in 
conjunction with an analog to digital converter (sometimes called a "frame 
grabber" device), the signal point or linear array scanning is no longer 
required to acquire a pixel array of digital values for a photogrammetric 
computer image of a hard copy photograph, transparency, drawing, or the 
like. The physical spacings and sizes of the pixels are fixed by the 
geometric CCD or CID array and by the magnification of the hard copy image 
to the CCD or CID array. 
These "frame grabbing" solid state cameras typically have rectangular 
arrays, such as, for example, about 510.times.492 CCD's or CID's. When 
properly focused on an image, each CCD or CID in the array detects light 
intensity from an individual spot or pixel area on the film image. Thus, a 
solid state camera that has an array of 510.times.492 CCD's on a 
rectangular chip will convert the portion of a film image within a focused 
frame to a square pixel array of 510.times.492, i.e., about 250,920 light 
intensity measurements or signals. Such an array of intensity measurements 
can, of course, be recorded and displayed by a computer on a CRT in the 
same pixel array to provide a computer image reproduction of the portion 
of the film image within the focused or "grabbed frame". There has been a 
recent announcement by at least one manufacturer that a solid state CCD 
camera with a 1,000.times.1,000 pixel array will soon be available, which 
will provide larger "grabbed" frames, more accuracy, or a combination of 
both. 
While the "frame grabbing" solid state cameras with rectangular CCD or CID 
arrays eliminate scanning, as described above, they are applicable only 
where a limited size pixel array is needed. For example, such a "frame 
grabber" may be useful in focusing onto, and acquiring a digital image of, 
a particular small object, such as an airplane, that can be seen in an 
aerial photograph of a ten square kilometer area. However, they have not 
been useful before this invention for "grabbing" and digitizing larger 
film image areas. In order to "grab" and digitize a larger film image 
area, the solid state camera had to be focused over a larger film area, 
thus sacrificing detail accuracy, since each pixel size within the array 
also is focused over a larger area. 
There are at least two products now available that can create a large pixel 
array by combining a "frame grabbing" two-dimensional image array with a 
scanning motion. In such systems, individual frames or sub-areas of larger 
macro-areas of film or paper photographs can be "grabbed" or digitized and 
stored. Then, adjacent frames can be "grabbed" and positioned correctly in 
the computer memory by either (1) moving the "frame grabbing" solid state 
camera very precisely to a predefined adjacent position mechanically and 
then "grabbing" the pixel array for that adjacent position, or (2) by 
moving the camera less precisely to "grab" the image at the adjacent 
location and relying on a precisely located grid mark or pattern of grid 
marks to geometrically relate one "grabbed" sub-area to the next "grabbed" 
sub-area. The "Autoset-1" manufactured by Geodetic Services Incorporated, 
of Melbourne, Florida is an example of the former of these techniques, and 
the "Rolleimetric RS", manufactured by Rollei Fototechnic GmbH, of 
Braunschweig, West Germany, is an example of the latter technique. 
In general, reasonable priced opto-mechanical scanners have not been able 
to achieve the accuracy considered to be necessary for many of the 
newly-evolving applications. Scanners that could achieve high geometric 
resolution are slow and often force a user to resort to an off-line 
scanning process separate from the process of actually using and analyzing 
the data. 
Frame grabbing solid state camera systems, as described above, provide a 
higher degree of accuracy within a small frame pixel array sub-area. 
However, combining frame grabbing with scanning to get digital data over a 
larger macro-area again usually sacrifices accuracy for economy or economy 
for accuracy due to the need for highly accurate mechanical position 
control. The Rollei system mentioned above, and further described in the 
West German Pat. No. DE 3428325, is considered to be a significant 
advancement in this regard by teaching the use of reseau grids in 
combination with a "frame grabbing" solid state camera, but it still 
requires manual identification of reseau grids or crosses. Also, the 
reseau crosses or grids are visible in the image and obliterate some of 
the contents of the photographic image where the grid marks are located. 
Also, the process of using a reseau in that manner is slow. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a fast, 
accurate, yet relatively inexpensive image digitizing and mensuration 
system for analyzing hard copy photographic, transparency, paper drawing, 
radar, and other images. 
A more specific object of the present invention is to provide an improved 
mensuration frame grabbing system for digitizing and analyzing hard copy 
photographic, transparency, paper drawing, radar, and other images. 
A still more specific object of the present invention is to provide an 
improved reseau grid for a mensuration frame grabbing system in which the 
reseau grid does not obscure or cover any part of the image and does not 
become a part of the image. 
Another specific object of the present invention is to provide a frame 
grabbing digitizing mensuration system that uses a reseau grid location 
reference system in which individual reseau detection and location is 
automatic. 
Still another specific object of this invention is to provide an image 
digitizing system in which one or more specific sub-areas of a large 
macro-area image can be converted to digital format without having to 
convert the entire macro-area image to digital format if not desired, thus 
avoiding the use of unnecessary computer storage and off-line creation of 
a large pixel array and allowing mass storage of currently uninteresting 
image to be kept on film only, yet which also has the capability of 
digitizing an entire large format macro-area image, if desired, in an 
efficient, accurate manner. 
A further specific object of the present invention is to provide a system 
that can quickly and accurately digitize a select feature shown in stereo 
photographs, correlate the digital images, and display them in a stereo 
image, such as a three-dimensional display or other stereo overlapping 
images, on a CRT, graphic display device, or the like. 
A still further object of the present invention is to provide a relatively 
inexpensive, compact apparatus for digitizing and analyzing hard copy 
images in which all parts of a large hard copy image are kept visible and 
stationary at all times. 
Additional objects, advantages, and novel features of this invention are 
set forth in part in the description that follows, and in part will become 
apparent to those skilled in the art upon examination of the following 
specification or may be learned by the practice of the invention. The 
objects and advantages of the invention may be realized and attained by 
means of the instrumentalities and in combinations particularly pointed 
out in the appended claims. 
To achieve the foregoing and other objects and in accordance with the 
purposes of the present invention, as embodied and broadly described 
herein, the apparatus of this invention includes a transparent reseau 
plate that has grid mark grooves in one of its surfaces, side lights 
around the edges of the reseau plate for illuminating the grid marks, and 
a bottom light for illuminating the object. The apparatus can also include 
a transparent object mounting plate over the bottom light for holding the 
object. The grid mark grooves can be etched into the reseau plate surface. 
A diffusion plate for evenly distributing the bottom light on the object 
can be placed between the bottom light and the object mounting plate. The 
side lights and bottom lights can be turned on and off in sequence to 
illuminate the grid marks and the object as desired.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The mensuration frame grabbing apparatus 10 according to the present 
invention is comprised of a translation mounting structure in which a 
solid state camera 140 can be moved in orthogonal X, Y and Z directions in 
relation to a reseau assembly 150. An object or image 176 to be digitized 
for computer storage, manipulation, and analysis, such as a photograph, 
map, film transparency, radar image, or the like can be mounted in the 
reseau assembly. The reseau assembly 150 includes a reseau plate 160 that 
contains a plurality of grid mark grooves 162, preferably in the shape of 
crosses, which are utilized to mark and coordinate spatial locations of 
the image on the object 176, as will be described in more detail below. 
One of the significant eatures of this invention is the manner in which 
the grid mark grooves are created and utilized, as will be described in 
more detail below. 
Referring now to FIGS. 1, 2, 3, and 4, the mensuration frame grabbing 
apparatus 10 has a superstructure frame or table 11 that is comprised of 
four upright corner members 12, 14, 16, and 18. The tops of these corner 
frame members 12, 14, 16, 18 are connected together in a rectangular 
manner by an elongated top front frame member 20, an elongated top rear 
frame member 24, an elongated top left side frame member 28, and an 
elongated top right side frame member 32. Similarly, the bottom ends of 
the corner frame members 12, 14, 16, 18 are connected together by an 
elongated bottom front frame member 22, an elongated rear bottom frame 
member 26, an elongated bottom left side frame member 30, and an elongated 
bottom right side frame member 34. This superstructure forms the framework 
or table 11 on which the other operating components of the apparatus 10 
are mounted. Footpads 36, 37, 38, 39 are provided under the corners for 
supporting, leveling, and, if preferred, cushioning the apparatus from 
shock and vibration. 
The top front frame member 20 and the top rear frame member 24 of the table 
11 described above also function as the X direction translation structure 
for the camera carriage assembly 100, as will be described in more detail 
below. A Y-axis translation platform assembly 50 is supported by the frame 
members 20, 24 and provides the Y axis translation mounting for the camera 
carriage assembly 100. A double Z-axis mounting structure 80 is mounted in 
the platform assembly 50, as will be described in more detail below. 
The camera carriage assembly 100 is mounted in the double Z-axis mounting 
structure 80 in such a manner that it moves vertically upwardly and 
downwardly in relation to the reseau assembly 150. Also, a lens carriage 
assembly 120 is mounted on the camera carriage assembly 100 within the 
double Z-axis mounting structure 80 in such a manner that also is movable 
upwardly and downwardly in the Z-axis direction in relation to the camera 
carriage assembly 100. As a result, when a solid state camera 140 is 
mounted on the camera carriage assembly 100, and the lens assembly 142 is 
mounted on the lens carriage assembly 120, both the camera 140 and the 
lens assembly 142 can be moved in unison upwardly and downwardly in 
relation to the reseau assembly 150, or the lens assembly itself can be 
moved upwardly and downwardly in the Z-axis direction in relation to both 
the camera 140 and the reseau assembly 150, as desired. This double Z-axis 
translational ability allows optimum camera positioning and lens focusing 
for achieving an optimum of desired magnification and high-quality 
transformation of selected parts of the image on object 176 into digital 
data for computer storage, manipulation, recall, and display. 
With continuing reference to FIGS. 1, 2, 3, and 4, the top front frame 
member 20 and the top rear frame 24 are each fabricated preferably of 
elongated channel-shaped structures. An elongated trackway or rail 40 is 
positioned substantially along the entire length on the top surface of 
frame member 20. Likewise, a similar elongated rail or trackway 42 is 
positioned along substantially the entire length on the top surface of 
frame member 24. These trackways 40, 42 serve as the support surface for 
the platform assembly 50 in such a manner that the platform assembly 50 
can translate leftwardly and rightwardly in the direction of the X-axis. 
The X-axis drive assembly 70 is positioned in the channel-shaped frame 
member 20 and is connected to the platform assembly 50, as will be 
described in more detail below, for moving the platform assembly 50 in a 
very controlled manner in the direction of the X-axis. 
The platform assembly 50 has a rigid frame structure comprised of elongated 
left side channel member 56 and elongated right side channel member 58 
connected together in spaced apart relation to each other by front channel 
member 52 and rear channel member 54 to form a rigid rectangular frame 
structure. Cage guides 60, 62, 64, 66 are permanently affixed under 
opposite corners of the rectangular frame structure of platform assembly 
50 to support the platform assembly 50 in a confined, slideable manner on 
the trackways 40, 42. Specifically, the front cage guides 60, 62 are 
slideably mounted on the front trackway 40, and the rear cage guides 64, 
66 are slideably mounted on the rear trackway 42. These trackways and cage 
guides are configured in such a manner that the platform assembly 50 can 
slide longitudinally leftwardly or rightwardly in the direction of the 
X-axis, but it is constrained against movement in any other direction. 
As best seen in FIG. 2, the X-axis drive assembly 70 is mounted in the 
channel-shaped frame member 20. A bracket 79 is rigidly attached to the 
underside of front frame member 52 of platform assembly 50 and extends 
downwardly to a position adjacent the channel member 20. A stepper motor 
72 mounted in the channel member 20 is connected by a coupler 73 to an 
elongated lead screw rod 76 that extends substantially along the length of 
channel member 20. The screw rod 76 is supported at each end by journal 
bearings 74, 75, which are also attached to the inside of the 
channel-shaped frame member 20. The screw rod 76 also extends through and 
engages a ball nut 78 that is attached to the bracket 79. Therefore, when 
the screw rod 76 is turned in one direction by the stepper motor 72, the 
ball nut 78 and bracket 79 pull the platform assembly 50 in one direction 
along the X-axis, and when the stepper motor 72 turns the screw rod 76 in 
the opposite direction, the platform assembly 50 is likewise moved in the 
opposite direction along the X-axis. 
Referring again to all of FIGS. 1, 2, 3, and 4, it can be seen that the 
double Z-axis mounting structure 80 is positioned in the space between the 
left and right frame members 56, 58 of platform assembly 50. The principal 
structural component of the double Z-axis is preferably an elongated, 
rigid channel member 82, which provides a mounting structure for a camera 
carriage assembly 100 and a lens carriage assembly 120, both of which will 
be described in more detail below. 
As best seen in FIG. 5, in conjunction with FIGS. 1 and 4, the channel 
member 82 of the double Z-axis mounting structure 80 is positioned between 
the left and right frame members 56, 58 in such a manner that it can be 
moved or translated in the direction of the Y-axis. A pair of angle iron 
brackets 84, 88 rigidly affixed to opposite sides of the channel member 82 
extend outwardly in opposite directions into the channel frame members 56, 
58, respectively. A pair of rails or trackways 68, 69 are positioned over 
the angle iron brackets 84, 88 and affixed to the respective top flanges 
of the channel frame members 56, 58. A left cage guide 86 is affixed to 
the top flange of the angle iron bracket 84 in a position to slideably 
engage the trackway 68. Likewise, a right cage guide 89 is affixed to the 
top flange of angle iron bracket 88 in a position to slideably engage the 
trackway 69. Therefore, the double Z-axis mounting structure 80 is 
effectively suspended from the trackways 68, 69 in such a manner that it 
is slideably movable forwardly and backwardly along the direction of the 
Y-axis, but is restrained against movement in any other direction in 
relation to the platform 50. 
The double Z-axis mounting structure 80 is moved back and forth in the 
direction of the Y-axis by the Y-axis drive apparatus 90. This Y-axis 
drive mechanism 90 is comprised of a stepper motor 92 connected to an 
elongated screw rod 96 by a coupling 93. The screw rod 96 is mounted in 
the left channel frame member 56 of platform 50 by journal bearings 94, 95 
positioned respectively at opposite ends of the screw rod 96. The 
midportion of the screw rod 96 passes through an ear 85 in bracket 84. A 
ball nut 98 in the ear 85 engages the threads of the screw rod 96 in such 
a manner that rotational movement of the screw rod 96 moves the channel 
member 82 of the double Z-axis mounting structure 80 along the Y-axis. 
Therefore, actuation of the stepper motor 92 in one direction causes the 
double Z-axis mounting structure 80 to move forwardly in the platform 50, 
and actuation of the stepper motor 92 in the opposite direction causes the 
double Z-axis mounting structure 80 to more rearwardly in the platform 50. 
Referring now primarily to FIGS. 4 and 5, the double Z-axis mounting 
structure 80 includes a camera carriage assembly 100 and a lens carriage 
assembly 120. Both the camera carriage assembly 100 and the lens carriage 
assembly 120 have separate drive assemblies 110, 130, respectively, to 
move them upwardly and downwardly either together or semi-independently in 
the direction of the Z-axis. Specifically, the camera carriage assembly 
100 is slideably mounted in the channel member 82 in such a manner that it 
can be moved upwardly and downwardly in the direction of the Z-axis by the 
camera assembly drive apparatus 100. The lens carriage assembly 120 is 
slideably mounted on the camera carriage assembly 100 in such a manner 
that it can be moved upwardly and downwardly in the direction of the 
Z-axis in relation to the camera carriage assembly 100 by the lens 
carriage drive apparatus 130. The solid state camera 140 is mounted on the 
camera carriage assembly 100, and the lens assembly 142 is mounted on the 
lens carriage assembly 120. Therefore, the distance between the lens 142 
and the camera 140 can be adjusted for desired magnification by actuating 
the lens carriage drive mechanism 130. Then, when the desired distance 
between the lens 142 and camera 140 is attained, the entire assembly of 
the camera 140 and lens 142 can be moved as a unit upwardly and downwardly 
in relation to the reseau assembly 150 for proper focusing. 
The camera carriage assembly 100 is comprised of a vertically oriented 
plate 102 positioned in the channel member 82 with a horizontal camera 
mounting bracket 108 extending laterally outwardly from the plate 102. A 
pair of trackways 103, 104 are affixed to the inside surface of the web 
portion of channel member 82. Each of the trackways 103, 104 is positioned 
in a vertical orientation and in parallel spaced apart relation to each 
other. A pair of cage guides 106, 107 are affixed to the plate 102 in 
positions where they slideably engage the trackways 103, 104, 
respectively. Therefore, the plate 102 and camera mounting bracket 108 are 
movable upwardly and downwardly on the trackways 103, 104, while being 
restrained against movement in any other direction in relation to the 
channel member 82. The solid state camera 140 is mounted on the camera 
mounting plate 108 so that it also moves upwardly an downwardly along with 
the plate 102. 
The camera carriage drive assembly 110 is comprised of a reversible stepper 
motor 112 connected to an elongated screw rod 116 by a coupler 113. The 
screw rod 116 extends through an ear 115 affixed to the plate 102 where it 
is threadedly engaged by a ball nut 118 mounted in the ear 115. A bearing 
block 114 attached to the channel member 82 supports the screw rod 116. 
Therefore, actuation of the stepper motor 112 in one direction moves the 
camera carriage assembly 100 upwardly, and actuation of the stepper motor 
112 in the opposite direction moves the camera carriage assembly 100 
downwardly in relation to the channel member 82. 
The lens carriage assembly 120 is comprised of a vertically oriented plate 
122 positioned adjacent the forward surface of the plate 102 of camera 
carriage assembly 100. A horizontal shelf 128 extends outwardly and 
laterally from the bottom edge of plate 122 to a position directly under 
the camera 140, and a brace member 129 helps to support the shelf 128 in a 
rigid, nonmovable manner in relation to the plate 122. An elongated 
trackway 124 is affixed in a vertical orientation to the front face of 
plate 102. A cage guide 126 is affixed to the rear surface of plate 122 in 
a position where it slideably engages the trackway 124. Therefore, the 
lens carriage assembly 120 is moveable upwardly and downwardly on trackway 
124 in relation to the plate 102, but it is restrained from movement in 
any other direction in relation to plate 102. The lens assembly 142 is 
mounted on the shelf 128 directly under the camera 140 so that it also 
moves upwardly and downwardly along with the lens carriage assembly 120 on 
the trackway 124. 
The lens carriage drive assembly 130 is comprised of a reversible stepper 
motor 132 mounted on the plate 102 and connected by coupler 133 to an 
elongated screw rod 136. A journal bearing 134 attached to the plate 102 
supports the screw rod 136. The screw rod 136 also extends through a 
bracket 135 rigidly attached to the front face of plate 122. A ball nut 
138 mounted in bracket 135 trhreadedly engages the screw rod 136. 
Therefore, actuation of the stepper motor 132 in one direction causes the 
lens carriage assembly 120 to move upwardly in relation to the camera 
carriage assembly 100, and actuation of the stepper motor 132 in the 
opposite direction causes the lens carriage assembly 120 to move 
downwardly in relation to the camera carriage assembly 100. An expandable 
and contractable tubular envelope or light shroud 144 is shown attached at 
its upper end to the camera mounting bracket 108 and at its bottom end to 
the lens shelf 128. This envelope 144 keeps extraneous light out of the 
optical path between the lens 142 and camera 140. 
Referring again to FIGS. 1 through 5, the reseau assembly 150 can be 
mounted by brackets 152, 153, or any other appropriate mounting structure, 
to the frame members 22, 26 in such a manner that the reseau assembly 150 
is positioned under the solid state camera 140 and lens 142. Therefore, as 
can be appreciated from the description above, the X-axis drive assembly 
70 and Y-axis drive assembly 90 can move the camera 140 and lens 142 to 
any desired position over the reseau assembly 150. Further, the camera 
carriage drive assembly 110 can move the camera 140 and lens 142 in unison 
upwardly and downwardly in relation to the reseau assembly 150 as desired. 
Further, as described above, the lens carriage drive assembly 130 can move 
the lens 142 upwardly and downwardly in relation to the camera 100 as 
desired. 
The reseau assembly 150 is best described by reference primarily to FIG. 6 
in combination with FIGS. 1, 3, and 4. A transparent object support plate 
172 is mounted horizontally in the lower fixed portion 156 of a frame 154. 
An object 176, such as a photograph, film transparency, map, or the like 
can be positioned on the upper surface of the object support plate 172. A 
reseau plate 160 is then positioned directly on top of the object 176 and 
clamped in place by the upper portion 155 of frame 154. The upper portion 
155 of frame 154 is hinged to the bottom portion 156 by a hinge assembly 
157 to accommodate convenient removal of the reseau plate 160 and object 
176 from the surface of the object support plate 172. The reseau plate 160 
includes a plurality of grid marks 162, preferably in the shape of 
crosses, in a precisioned measured pattern on its bottom surface. The 
structures and usage of these grid marks 162 will be described in more 
detail below. 
A bottom light assembly 180 is positioned under the reseau assembly 150. 
This bottom light assembly 180 can be comprised of a plurality of 
fluorescent bulbs 186 or other suitable light sources. The fluorescent 
bulbs 186 are shown mounted in sockets 184 attached to brackets 182. These 
bottom assembly lights include power and switch components (not shown) for 
turning the bottom lights on and off as desired. A translucent diffusion 
plate 174 is preferably positioned under the object support plate 172 and 
mounted in lower portion 156 of frame 154. The diffusion plate 174 
disperses light from the bottom light assembly uniformly over the entire 
surface area of the object support plate 172. 
As best shown in FIGS. 6 and 7, with secondary reference to FIG. 1, the 
reseau assembly 150 also includes a side light source preferably in the 
form of a fluorescent light tube 170 positioned in a trough 158 in the 
bottom section 156 of frame 154 and extending around the perimeter of the 
reseau plate 160. A light canal 159 in the form of a space between the 
upper and lower sections 155, 156 of frame 154 allows light rays 190 from 
the side light 170 to reach the edge of reseau plate 160. 
A significant feature of this invention is the combination of the structure 
of the grid marks 162 with the sidelights 170 to make the grid marks 
visible or invisible as desired. Referring now to FIGS. 7 and 8, the 
preferred grid mark structure 162 of the present invention is in the form 
of a "+"-shaped groove precision etched into the bottom surface of the 
reseau plate 160. The bottom surface is preferred so that the grid marks 
are positioned directly on the optical plane of the object 176, thus 
eliminating fuzziness due to focusing on the plane of the object. These 
etched grooves preferably have a generally trapezoidal cross-sectional 
configuration with generally inwardly slanted opposite sidewalls 163, 164 
intersected by a generally flat top wall or surface 165. The width of the 
open bottom of the groove is preferably in the range of 25 to 100 .mu.m, 
and the depth of the groove is preferably in the range of about 2 to 10 
.mu.m. 
Because of the shape of the groove of this reseau grid mark 162, a 
substantial part of the light rays 190 directed horizontally through the 
plane of the transparent reseau plate 160 from the side lights 170 are 
reflected and refracted upwardly from the slanted sides 163, 164 of the 
reseau mark groove 162. The upwardly reflected and refracted light rays 
from the slanted surface 163 are indicated schematically in FIG. 8 as 
light rays 191, 192. Likewise, the upwardly reflected and refracted light 
rays from slanted surface 164 are indicated schematically as rays 193, 
194. 
These upwardly directed light rays 191, 192 from slanted surface 163 and 
light rays 193, 194 from the slanted surface 164 are directed into the 
lens 142 positioned over the surface of the reseau plate 160. The CCD or 
CID detectors in a rectangular array in the solid state camera 140 (not 
shown in FIGS. 7 and 8) can, of course, detect the spatial positions and 
intensities of these upwardly directed light rays 191, 192, 193,194 very 
accurately, particularly when the bottom lights 180 are turned off so that 
the only source of light is from the side light 170. As shown in FIG. 8, a 
plot 202 of light intensity in relation to spatial location on the edge of 
a transverse plane cutting through the grid mark 162 as "seen" or detected 
by the solid state camera 140 results in two peak intensities 204, 206 
spaced apart from each other in the same spatial distance as the distance 
between the slanted sides 162, 164 of the etched reseau groove 162. 
Such a solid state camera "view" in terms of light intensity can be 
converted to digital data corresponding to specific pixel locations on the 
surface of the reseau plate 160 for processing. The processing can include 
setting a threshold intensity 208 above which the peak intensities 204, 
206 are recorded and stored by computer in correlation with their spatial 
locations, and below which the intensities are ignored. The resulting 
image recorded and stored in the computer, therefore, corresponds to the 
edges of the grid mark grooves 162. The edge boundaries 195, 196 of the 
recorded peak 204 above the threshold 208 can essentially correspond with 
the lateral extremities of the slanted surface 163 so that the width 
between the boundary edges 195, 196 represents the width 197 of the 
spatial location recorded on that side of the reseau grid mark 162. 
Likewise, the edge boundaries 198, 199 of the peak 206 above the threshold 
208 correspond generally with the lateral extremities of the slanted 
surface 164 and define the width 200 in spatial location of that side of 
the grid mark 162. The resulting data and computer memory therefore 
corresponds with the boundary lines of the grid mark 162, as illustrated 
in FIG. 9. As described above, the intensity peaks 204, 206 correspond 
with the grid mark boundary lines 197, 200. Likewise, additional intensity 
peaks 228, 230, 232, 234, 236, 238 correspond in spatial location with 
boundary lines 229, 231, 233, 235, 237, 239, respectively, of the grid 
mark 162. 
An alternate embodiment grid mark 162.degree. is shown in FIG. 10. This 
alternate grid mark 162' is similar to the preferred embodiment grid mark 
162 described above in that it is formed by etching a groove into the 
bottom surface of the reseau plate 160. However, in this alternate 
embodiment grid mark 162', the side surfaces 163', 164' and the top 
surface 165' are etched in such a manner that they are more rough and 
irregular instead of substantially smooth surfaces. Therefore, the light 
rays 190 traveling longitudinally through the transparent reseau plate 160 
from the sidelights 170 are more scattered as they are reflected and 
refracted generally upwardly through the top surface of the reseau plate 
160. For example, as illustrated in FIG. 10, the scattered generally 
upwardly directed light rays 210 result from the longitudinal light rays 
190 incident on the right side 163' and top 165' of the etched grid mark 
162'. Likewise, the generally upwardly directed scattered light rays 212 
result from the longitudinal light rays 190 incident on the right side 
164' and top 165' of the grid mark 162'. As a result, the light intensity 
"seen" or detected by the solid state camera 140 may still have two spaced 
apart peaks 222, 224 generally corresponding in spatial location with the 
sides 163' 164' of grid mark 162', but the intensity 223 between the two 
peaks 222, 224 also remains substantially higher than the background light 
intensity level 220. Therefore, the threshold intensity level 226 can be 
set between the valley intensity level 223 and background intensity level 
220. In this manner, the recorded spatial locations of pixels having light 
intensity greater than the threshold 226 is bounded by the edges 214, 215 
corresponding to the entire width 216 of the grid mark 162'. The result, 
as shown in FIG. 11, is that the spatial conditions recorded by the solid 
state camera where the light intensity is above the threshold 226 
corresponds with the entire width of the grid mark 162' showing as a broad 
line 216. Similar light intensity levels at peaks 262, 264 and the valley 
263 therebetween above the threshold 226 are recorded in the computer 
memory as the broad line 265 corresponding with the cross portion of the 
grid mark 162'. Consequently, the grid mark 162' stored in the computer 
memory as the full width grid mark 162' rather than just the borderlines 
of the grid mark that were shown for the preferred embodiment 162 in FIG. 
9. 
An advantage of the grid marks 162 and 162' as described above is that 
after they have been recorded in the computer memory, they can essentially 
become invisible so as not to interfere with or block out any part of the 
image on the object film, transparency, or photograph 176 as its image is 
being digitized and recorded in the computer memory. These grid marks 162 
and 162' can be made invisible simply by turning off the side light 170. 
Because the slanted sides 163, 164 are fairly steep, there is virtually no 
noticeable interference with the light rays 188 produced from the bottom 
light 180, as shown in FIG. 7, as those bottom light rays 188 travel 
upwardly through the reseau plate 160 to the camera lens 142. Therefore, 
after the object 176 is positioned on the object support plate 172 and the 
reseau plate 160 is positioned on top of the object 176, the whole 
assembly can be clamped into position with the top portion 155 of frame 
154. Then, with the bottom light assembly 180 turned off and the 
sidelights 170 turned on, the camera 140 can be turned on to detect the 
precise position of the grid marks 162 or 162'. This data corresponding 
with the positions of the grid marks 162 or 162' is then sent to and 
stored in the computer memory. After the grid mark positions have been 
recorded and stored in computer memory, the sidelights 170 are turned off 
and the bottom lights 180 are turned on. With the sidelights 170 off and 
the bottom lights 180 on, the camera 140 can be used to detect the light 
intensities of the bottom light rays 188 allowed through the various parts 
of the object 176 as dictated by the image thereon, which intensity data 
is then sent to the computer processed and put into computer memory as 
digital data corresponding with the image on the object 176. As mentioned 
above, this data corresponding with the image on the object 176 does not 
include the data corresponding to the grid marks 162 or 162'. Therefore, 
the entire image detected from the object 176 is recorded in memory 
without any portion thereof being blocked out or interfered with by the 
grid marks 162 or 162'. Yet the computer memory has stored therein data 
relating to the precise spatial location of the grid marks 162 or 162' in 
relation to the image from the object 176 for use in locating, scaling, 
measuring, analyzing, correlating, or displaying the image in precise 
terms. 
Another alternative embodiment grid mark 162" according to the present 
invention is shown in FIG. 12. This alternative grid mark 162" is made by 
etching a groove in the bottom surface of the reseau plate 160, similar to 
that described in the preferred embodiment grid mark 162 shown in FIG. 8 
above. However, in this alternate embodiment grid mark 162", the groove is 
filled or partially filled with an opaque substance, such as ink 168. 
Therefore, the light rays 188 emanating from the bottom lighting system 
180 cannot pass all the way through the reseau plate 160 to reach the 
camera 140 where those light rays 188 are blocked by the opaque ink 168 in 
the grid mark 162". 
Consequently, as shown by the plot 271 in FIG. 12, the intensity of the 
light detected by the solid state camera falls off almost to zero, as 
indicated by the valley 272 in the plot 271 where the light rays 188 are 
blocked by the grid mark 162". The computer can be programmed, therefore, 
with a threshold intensity level 270 below which the computer will 
recognize it as a grid mark. As a result, the spatial location between the 
broken lines 273, 274 can be interpreted by the computer to correspond 
with the grid mark 162". While this alternate embodiment opaque grid mark 
162" is functional, it has the disadvantage of also blocking out and 
making illegible any part of the image on the object 176 that happens to 
lay just under the grid mark 162". Of course, the sidelights 170 are not 
required for use of this alternate embodiment grid mark 162". 
Three planar coordinate systems are used in association with mensuration 
operations with the apparatus 10 according to this invention. These three 
coordinate systems are illustrated in FIG. 15 in conjunction with the 
reseau plate 160, grid marks 162, and a view frame 240 as "seen" by the 
camera. First, there is a table coordinate system, indicated at 280, which 
is a measure or indication of the physical position or spatial location of 
the camera 140 and lens 142 on the X-axis and Y-axis in relation to the 
table 11 and platform 50. Specific locations of the camera 140 and lens 
142 on this table grid system are indicated by either (1) keeping track of 
stepper motor turns, which result in specifically measured linear movement 
increments, or (2) locator devices, such as electro-optic devices (not 
shown) mounted on the structure. Second, there is the image coordinate 
system, indicated at 282, which is a measure or indication of the spatial 
locations of parts of the image in relation to other parts of the image or 
to a benchmark on the image. Specific locations on this image coordinate 
system 282 are provided by the array grid marks 162 on the reseau plate 
160 as discussed above. Third, the frame coordinate system, indicated at 
284, is a measure or indication of the locations of specific pixels of 
light intensity within the frame "seen" by the solid state camera. 
Specific locations of pixels in this frame coordinate system are indicated 
by the specific CCD or CID light sensor element within the array of such 
light sensor elements in the camera. As discussed above, typical chips 
commonly used in the solid state "frame grabbing" cameras have a plurality 
of light sensor elements arranged in rectangular two-dimensional arrays 
of, for example, 510.times.492, although arrays of 1000.times.1000 light 
sensors are also coming available. These three coordinate systems 280, 
282, 284 are all synchronized and utilized together according to this 
invention, to achieve precise spatial integration and mensuration of parts 
of all of the image on an object 176. In addition, the position of the 
camera 140 and lens 142 in the Z-axis is also integrated with these planar 
coordinate systems for magnification and scale used in a particular 
operation or image analysis. 
As discussed above, the camera 140 and lens 142 are driven to desired 
positions in the X-Y plane on the table coordinate system by the X-axis 
drive apparatus 70 and the Y-axis drive apparatus 90. The lens 142 is 
driven upwardly and downwardly in the Z-axis direction in relation to the 
camera 140 by the lens carriage drive assembly 130. The camera 140 and 
lens 142 are driven in unison upwardly and downwardly in the Z-axis 
direction by the lens carriage drive apparatus 110. Each of these drive 
apparatus 70, 90, 110, 130 has a stepper motor 72, 92, 112, 132, 
respectively, with an encoder mounted on each stepper motor to detect 
motion of the respective motor shafts. An accurate record of rotation 
increments of each stepper motor is available from each respective stepper 
motor controller, which is a standard component of known stepper motor 
systems. 
Each of these drive apparatus 70, 90, 110, 132 also has a home position 
locator or sensor to detect when the drive apparatus, thus the component 
driven in the X, Y, or Z axis, is in a "home" position. While these home 
position locators or sensors are not shown in the drawings, such sensitive 
sensors as opto-interruptors and the like are well-known and readily 
available items. For example, an LED and a photodiode can be mounted in 
spaced apart relation to each other on a frame member 20 of the table 
structure 11, and an opaque object can be mounted on the platform 50 in 
alignment with the space between the LED and the photovoltaic cell and 
adjusted so that it blocks the light from the LED from reaching the 
photodiode when the "home" X-axis position of the platform 50 is reached. 
The interruption of light is detected and can be processed to a "stop" 
signal in a manner known to persons skilled in the electronics art for 
deactuating or turning off the stepper motor 72. Likewise such 
opto-electronic "home" position sensors can be mounted on the platform 50 
and channel member 82 for turning off the stepper motor 92 when the Y-axis 
"home" position is reached, on the channel member 82 and camera carriage 
assembly 100 for turning off stepper motor 112 when the camera Z-axis 
"home" position is reached, and on the camera carriage assembly 10 and the 
lens carriage assembly 120 for turning off stepper motor 132 when the lens 
Z-axis "home" position is reached. 
An axis position controller system 350 is illustrated in the block diagram 
of FIG. 13. One of these controller systems 350 can be used for each drive 
apparatus 70, 90, 110, 130. These axis position controller systems 350 not 
only control the physical positions of the camera 140 and lens 142 in the 
X, Y, and Z axes, but they also provide the spatial location and 
magnification data to the computer system 100 for use along with the pixel 
position and light intensity data from the solid state camera 140 in 
mensuration and image display functions. 
A block diagram of a control system 310 called "CPRIME" according to this 
invention interfaced with a VAX 11/780 computer system 300 is shown in 
FIG. 14. This operator system 310 for the mensuration frame grabbing 
apparatus 10 includes four axis position controller systems 350, such as 
that shown in FIG. 13--one for each drive system. For convenience in 
describing this control system 310, the X-axis controller system is 
designated 351, the Y-axis controller system is designated 352, the camera 
Z-axis controller system is designated 354. Thus, the X-axis controller 
system 351 controls the X-axis drive 70, the Y-axis controller system 352 
controls the Y-axis drive 90, the camera Z-axis controller system 353, 
controls the camera carriage drive 110, and the lens Z-axis controller 
system controls the lens shelf drive 130. A standard interface 312, such 
as an RS-232C interface, is provided to connect the terminal drive 306 of 
computer 300 to the controllers 351, 352, 353, 354 via the address bus 
314, control bus 316, and data bus 318. The camera 140 is connected 
through a CDAX switch 320 to the frame grabber analog-to-digital converter 
304, such as a Gould FD- 3000 (trademark), can be a component of the 
computer system 100. An operator station 302, preferably comprising a 
keyboard and a CRT or graphical display device, is also connected to the 
terminal drive 306 of the computer 306. 
As mentioned above, where stereo mensuration or comparator mensuration is 
desired, two twin mensuration frame grabbing systems 10 according to the 
present invention are used. The second of the twin system 500 is not 
illustrated in detail because it can be essentially identical to the 
mensuration frame grabbing system 10 described in detail above. However, 
the control system 510 for the twin mensuration frame grabber system 10 is 
shown in the schematic diagram of FIG. 14 tied into the computer system 
100 in the stereo embodiment according to this invention. Specifically, 
the control system 510 of the twin mensuration frame grabbing system 500 
is shown in FIG. 14 much the same as the control system 310 of the 
mensuration frame grabbing 10. It includes four axis controllers, an 
X-axis controller 551, a Y-axis controller 552, and a lens Z-axis 
controller 554, for controlling the corresponding X-axis, Y-axis, camera 
carriage, and lens shelf drives (not shown) of the twin mensuration frame 
grabbing system 500. An interface 512 connects the controllers 551, 552, 
553, 554, via address bus 514, control bus 516, and data bus 518 to the 
terminal driver 306 of computer 300. Also, the solid state camera 540 of 
the twin mensuration frame grabbing system 500 is connected to the frame 
grabber A/D converter 304 through the CDAX switch 320. 
In order to obtain meaningful data from the mensuration frame grabbing 
system, it is necessary to orient the image with the table coordinate 
system. This initializing or "inner orientation" is accomplished after the 
object 176 and reseau plate 160 are loaded in the frame 154 and mounted in 
the table 11 by allowing the camera to seek its "home" position as defined 
by the opto-interrupter limit sensors mounted on the structure as 
described above. This "home" position in the X-Y plane establishes a zero 
point on the table coordinate system in the X and Y axes. 
In stereo mensuration, the bottom lights 180 are switched on and the side 
lights 170 are initially switched off as the camera 140 of one of the twin 
mensuration frame grabbing systems 10 is driven in the mono mode by drives 
70, 90 over its respective reseau assembly 150 until it is focused on the 
desired photo or other image area of the respective object 176. As the 
camera 140 moves, it grabs a frame of a portion of the image about every 
1/30th of a second. These image frames are constantly viewable on the 
computer CRT 302, so the operator can see when the camera 140 is focused 
on the desired image area on the object 176. 
Once the camera 140 of the first frame grabbing apparatus is focused on the 
desired image area, that image is grabbed and stored in computer memory 
and displayed on the CRT of the operator station 302. Then the bottom 
lights of the other of the twin mensuration frame grabbing systems 500 are 
turned on, and the camera of the system 500 is driven over its respective 
reseau assembly, which contains the photograph or other hard copy image 
that is the stereo conjugate of the photograph or other hard copy image 
that is mounted in the reseau assembly of the first system 10 until the 
camera of the second system 500 is focused on the corresponding image 
area. During this process, the digital data of image frames grabbed by the 
twin system 500 is merged by the computer and displayed together with the 
computer stored image grabbed by the first system 10. In this manner, 
stereo parallax removal from the two conjugate stereo images can be 
accomplished easily and precisely by the operator viewing the superimposed 
conjugate images, in spite of the somewhat less precise mechanical 
positioning information available from stepped increments of the 
respective axis drives. In other words, while the respective cameras 140, 
540 of the twin mensuration frame grabbing systems 10, 500 can be driven 
to about the same positions, either separately or concurrently, to the 
desired image area of the conjugate films to be viewed and analyzed, the 
precise conjugate position of the second camera 540 over the desired image 
area on the film in relation to the position of the first camera 140 does 
not have to be accomplished by precise placement of the respective 
conjugate films in the respective frame grabbing apparatus 10, 500 or by 
precisely coordinated and measured movement of the respective cameras 140 
540 to those conjugate areas of the films. Further, stereo-parallax 
removal does not have to be accomplished by the common, but slow and 
cumbersome method of shifting one of the images by software and rewriting 
it to the display, which is far too slow for real-time stereo-parallax 
removal. Instead, stereo-parallax removal is accomplished according to the 
present invention by hardware scroll, i.e., moving the second camera 540 
in relation to the image of the desired area grabbed by the first system 
10 and stored in computer 100 as both this stored image from the first 
system 10 and the image from the scrolling second camera 540 are displayed 
together superimposed on each other. In this manner, the operator can see 
on the CRT precisely when the conjugate image areas on the respective 
films or other objects on each of the two mensuration frame grabbing 
apparatus 10, 500 come together in a precise, sharply focused, stereo 
image. 
When both of the cameras are stopped on the desired stereo-viewable pair of 
conjugate images, the bottom lights 180 are turned off for a short time, 
so there is no film illumination. Simultaneously, the side lights 170 are 
turned on for grid illumination. With the side lights 170 on, each camera 
140 "grabs" a frame at the location where it was stopped, thus grabbing an 
image of the grid marks 162 within the frame "seen" by the camera 140. 
Each camera 140 feeds that "grabbed" image of the grid marks 162 to the 
computer. The computer can discern the specific spatial locations of the 
grid marks 162 in the frame coordinate system by the specific pixels of 
CCD light sensors in the CCD array in the camera 140 that sense the grid 
marks 162. Therefore, the grid marks 162 are automatically located within 
the frame and frame coordinates are computed. These frame coordinates are 
then used to compute coefficients of transformation for transforming the 
spatial locations of the grid marks 162 within the "grabbed" frame to 
table coordinates in relation to the "home" position using the known table 
coordinates of the grid marks. Thereafter, the grid marks 162 provide the 
image coordinate system so that any portion of the object 176 image within 
a "grabbed" frame that includes any grid marks 162 can be located in 
precise spatial orientation to other image portions "grabbed" or to the 
"home" position. The spatial measurements of subsequent camera 140 
movements by the encoder input and direction sensing logic shown in FIG. 
13 need only be accurate enough for the microprocessor to determine which 
grid marks 162 are within the subsequent "grabbed" frames. 
Since the sizes and distances between all the grid marks 162 etched into 
the reseau plate 160 are known very precisely and are also fed into the 
computer, the computer can precisely check and adjust the exact spatial 
locations of grid marks 162 in the subsequently "grabbed" frames to the 
grid marks 162 in previously "grabbed" frames or to the "home" position. 
In other words, using the coefficients of transformation and the known 
table coordinates of the grid marks 162, the image coordinates and 
segments "grabbed" can be related geometrically to the table coordinate 
system. 
After the image of the grid marks 162 within the "grabbed" frame for each 
camera 140, 540 are stored in computer memory, as described above, the 
side lights 170 are turned off, and the bottom lights 180 are turned back 
on. Then, without moving the cameras 140, 540 the same frame positions are 
"grabbed" again, this time "grabbing" the portion of the object 176 image 
within the frame. This image within the frame "grabbed" by each camera 
140, 540 is also sent to the computer 100 with each feature of the image 
"grabbed" being sensed in pixels by light intensity focused on individual 
CCD light sensors in the CCD array of each of the cameras 140, 540. 
Therefore, each camera 140, 540 feeds two images to the computer 100 for 
each frame position, i.e., the grid mark 162 image within the frame and 
the portion of the object 176, image within the frame. Since the cameras 
140, 540 do not move between "grabbing" these two images, the grid marks 
162 are in computer memory in precise spatial position on the "grabbed" 
segment of the object 176 image. However, since they were "grabbed" 
separately, first one and then the other, the grid marks 162 to not block 
out or distort any part of the object image. 
If the system has been initialized properly, as described above, such as by 
observation of a benchmark or even the film edge, the table coordinates 
can be transformed into film or image coordinates. For example, as 
illustrated in FIG. 15, if a frame 240 was "grabbed" at the "home" 
position, illustrated by dot 242 in the center of the frame 240, five grid 
marks 162 are "grabbed" in the frame 240. Each of those grid marks 162 are 
recognizable by the computer as being the grid marks 162 expected to be in 
a frame "grabbed" at "home" position 242 by the general positioning of the 
reseau plate 160 in the table 11. Even if the reseau plate 160 is not 
placed precisely in the same place each time, it is close enough if it is 
placed so at least the same reseau grid marks 162 can be captured within a 
frame "grabbed" at "home" position 242. This is not to say that a frame 
has to be "grabbed" at "home" position each time the apparatus 10 is 
initialized, but it could be used as a check on proper reseau plate 160 
positioning. As long as the reseau plate 160 is positioned each time close 
enough that the same grid marks 162 would be in the frame "grabbed" at 
"home" position if such a frame was "grabbed", spatial positions can be 
taken from any other grid marks 162 that appear in any other frame 
"grabbed" over other parts of the reseau plate 160, because the spacings 
and sizes of all the grid mark 162 on the reseau plate 160 are known 
precisely. 
To illustrate further, the four grid marks 162 "grabbed" in frame 240 at 
"home" position 242 in FIG. 15 are not shown exactly centered in the frame 
242. However, since the camera 140 is centered on the "home" position 240 
and the frame coordinate system is fixed by the CCD array in the camera, 
the actual pixels in which the five grid marks 162 in frame 240 can be fed 
to the computer 100, and a correction factor can be determined to "adjust" 
the positions of the grid marks 162 by software to ideal positions as if 
they were centered exactly around the "home" position 242, i.e., 
initializing the image coordinate system to the table coordinate system. 
Then, when the camera 140 is moved by stepper motors 72, 92 to an 
alternate position and a frame 240' is grabbed at that alternate position, 
the encoders of the stepper motors, 72, 92, along with the logic 
illustrated in FIG. 13, will keep track of distances and directions the 
camera 140 is moved. By correlating those distances and directions with 
the known spatial settings of the grid marks 162 on the reseau plate 160 
and keeping track of each such grid mark 162, e.g., by sequential (i,j) 
numbers in a cartesian coordinate system, and by applying the correction 
factor determined above, the computer will know or recognize which grid 
marks 162 show up in the image "grabbed" in the alternate 240'. Since the 
(i,j) image coordinates of those grid marks 162 within alternate frame 
240' are known along with their precise spatial position from "home" 
position, the computer can further correct or update actual table 
coordinates and pixel locations in relation to the image coordinates at 
that alternate "grabbed" frame 240' location. Therefore, when the side 
light 170 illumination of grid marks 162 is turned off and the bottom 
light 180 is turned on, the image segment "seen" by the camera 140 can be 
loaded precisely in spatial relation to any other "grabbed" image segment. 
Also, once the stereo initialization is completed, the cameras 140, 540 can 
be moved over the two conjugate images, respectively, and, upon stopping 
the cameras 140, 540 over a desired image segment, proper table and image 
coordinates for each pixel of the image segment can be obtained as 
described above so that stress-free stereo observation is feasible. Then, 
mensuration of image points can be done with a movable cursor in the 
digital image display. The image display is fixed or frozen in a desired 
scale, and the cursor movement is scaled to correspond with the scale of 
the image. As the cursor is moved over the frozen image, the distances 
moved to scale can be displayed. 
The mono-comparator mode of operation differs from the stereo mensuration 
mode described above only in that a single mensuration frame grabber 
apparatus 10 is used instead of two of them. The purpose of the 
mono-comparator mode is to create image coordinates of features that are 
desired to be analyzed or measured. A movable cursor can be used to point 
to specific points or features in a fixed or frozen image segment 
"grabbed" by the camera 140 and for mensuration of features in the image. 
The cursor can be moved manually or by automatic sweep to a target feature 
using pattern recognition. Transformation of pixel or frame coordinates 
into table coordinates and further into image coordinates is based on the 
reseau grid marks 162 and their automatic detection as soon as the camera 
140 stops in the same way as described above for the stereo mensuration 
mode. This procedure is applicable at any of the available magnifications. 
The comparator cursor movement in the CRT display window and the camera 
movement are smoothly controlled and coordinated according to this 
invention in such a manner that the cursor can be moved within a display 
window on the CRT of the grabbed image by appropriate user controls and, 
when the cursor reaches an edge of the display window, the X-axis and 
Y-axis drives 70, 90 start to drive the camera 140 over the film or object 
176 as the CRT simultaneously displays real-time video scroll images as 
the camera 140 moves. In other words, as illustrated in FIG. 16, the 
computer-generated cursor 250 is movable by the operator in any X or Y 
direction within the display window 252 of a CRT 254. Such movement can be 
controlled by a joystick switch, omni-directional ball switch (commonly 
called a "mouse"), designated keys on a keyboard at the operator station, 
or the like. Such cursor control switch devices are well-known in the 
computer art and need not be described in detail here. When the cursor 250 
is moved to display window limit or margin, such as the right margin 256, 
the X-axis controller 351 actuates the X-axis drive 70 to move the camera 
140 to the right. As the camera 140 moves to the right, it grabs images 
about every 1/30th of a second and continuously displays those images in a 
real-time scroll over the film or object 176 until the camera reaches the 
desired spot and the CRT 254 displays the desired image. The joystick or 
other control switch can then be manipulated to move the cursor away from 
the margin 256 and back into the display, at which time the controller 351 
deactuates the drive 70 and stops the movement or translation of the 
camera. 
Of course, movement of the cursor into other margins causes the camera to 
move or scroll in other directions. For example, movement of the cursor 
250 to the left margin 257 actuates X-axis drive 70 to move camera 140 to 
the left. Likewise, movement of the cursor 250 to either the top margin 
258 or the bottom margin 259 actuates the Y-axis drive to move the motor 
in those respective Y-axis directions. 
When the camera 140, is positioned to display the desired image, the side 
lights 170 are flashed to capture the grid image, the precise camera 
orientation with respect to grid marks 162 are determined and calibrated, 
as described above, and the cursor position can be calibrated to grid 
marks 162. Therefore, the cursor position coordinates can also be 
displayed. This operation can be programmed to occur upon pressing a 
designated "select" button or key on the keyboard (not shown). Succeeding 
cursor position coordinates calibrated to the scale and magnification of 
the image display can be used in making precise measurements of objects or 
spatial relationships in the display. 
The above-described motion and display sequence appears on the display CRT 
254 as a smooth operation, without spatial jumps in the course location or 
in successive image display during scrolling. It is also done quite 
conveniently with a minimum of operator controls or special training. 
This frame grabbing apparatus 10 can also be used to build up and store a 
large pixel array. For example, if an entire 20".times.10" (50 cm.times.25 
cm) film image needs to be digitized and stored, a series of adjacent 
frames of the image and reseau grid marks 162 can be grabbed, coordinated 
to one precise table and then to a precise composite image coordinate 
system, and then stored in computer memory. Such a 20".times.10" 
(50cm.times.25cm) image may require an array of 40,000.times.10,000 pixels 
of 12.5 .mu.m diameter. Since a solid state camera 140 that grabs an array 
of only about 510.times.492 pixels in its frame may cover only a fraction 
of the entire image, the goal is to "grab" a number of adjacent frames, 
e.g., of about 510.times.492 pixels and piece or mosaic, i.e., "file", 
them together to obtain the entire 40,000.times.20,000 pixel array of the 
whole image. 
This goal can be achieved according to the present invention by 
sequentially stopping the camera 140 in a systematic raster pattern under 
software control and "grabbing" adjacent frame segments of the image along 
with the grid marks 162 on those segments in the respective frames. Then, 
using the grid marks 162 and image coordinates, the individual frame data 
can be merged, i.e., "filed", together and converted into digital data for 
the entire 20".times.10" (50 cm.times.25 cm) image. In the example 
described above, a mosaic comprised of about 80.times.40 frames of 
510.times.492 pixels apiece would be required for the 40,000.times.20,000 
pixel array of the entire object image. 
Another use of the mensuration frame grabbing apparatus 10,500 of the 
present invention is to provide joint analysis and manipulation of 
separate, but related, image data sets. For example, it might be desirable 
to compare an older photo or map of an area with a more recent one, 
perhaps to detect changes or to update available information or images. 
Such an operation could be conducted in much the same manner as the stereo 
mensuration operation described above, except that an old image and a new 
image would be mounted in two separate mensuration frame grabbing 
apparatus 10,500, instead of two concurrently photographed images at 
different angles. Differences or changes between the old and new images 
can be detected visually on the CRT, or a computer could be programmed to 
detect such changes automatically. 
As mentioned above, the lens 142 and camera 140 combination has a variable 
magnification capability under manual or computer control. Such variable 
magnification preferably covers a range of about 12.5 .mu.m pixels to 125 
.mu.m pixels and still maintain the same logic of operation with automatic 
recognition of reseau grid marks 162 and automatic transformation of frame 
coordinates into table and image coordinates. To do so, the reseau plate 
160 is designed preferably so that at maximum magnification with the 
smallest pixel size of about 12.5 .mu.m, there will be five reseau grid 
marks 162 in each frame or field of view of the camera 140. Also, at 
minimum magnification with about 125 .mu.m diameter pixels, the reseau 
grid marks 162 and their spatial locations still have to be recognizable. 
The grid marks 162 having generally trapezoidal cross-sections etched into 
the bottom of the reseau plate 160 as described above are most appropriate 
for this purpose. 
The foregoing description is considered as illustrative only of the 
principles of the invention. Further, since numerous modifications and 
changes will readily occur to those skilled in the art, it is not desired 
to limit the invention to the exact construction and operation shown and 
described, and accordingly all suitable modifications and equivalents may 
be resorted to falling within the scope of the invention as defined by the 
claims which follow.