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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to digital photogrammetric processes and more
specifically to a method of photogrammetric image mensuration in which
grid marks can be provided, yet can be made invisible to an image of the
object to be mensurated and analyzed.
2. Background of the Invention
The photographic art for aerial surveillance, geological and archaelogical
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,
geological 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
controlled 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 of photographing 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 Puinix, of Sunnyvale, Calif. 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 techniqe.
In general, reasonably 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 subarea.
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 patent 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 embodimed and broadly described
herein, the method of this invention includes the steps of positioning a
reseau with grid marks on the object and sequentially illuminating the
grid marks separate from the object and illuminating the object separate
from the grid marks or in a manner that the grid marks are not visible
with the object. The image of the grid mark positions, when illuminated,
are digitized and store in computer memory and correlated with the image
of the object when it is illuminated and digitized. The scale of the image
can also be correlated to the scale of the grid marks.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects of the present invention will become more readily
appreciated and understood from a consideration of the following detailed
description of the preferred embodiment when taken together with the
accompanying drawings, in which:
FIG. 1 is a perspective view of the mensuration frame grabbing apparatus of
the present invention with portions of the components cut away in several
places to reveal the positions and structures of significant components of
the apparatus.
FIG. 2 is a front elevation view of the mensuration frame grabbing
apparatus with portions of the structure cut away to reveal the positions
and structures of significant components.
FIG. 3 is a right side elevation view of the mensuration frame grabbing
apparatus shown with several parts of the structure cut away to reveal the
positions and structures of significant components.
FIG. 4 is a plan view of the mensuration frame grabbing apparatus of the
present invention with portions of the structure cut away to reveal the
positions and structures of significant components.
FIG. 5 is a cross-sectional view taken along lines 5--5 of FIG. 4 to show
the components and structure of the double Z-axis drive apparatus;
FIG. 6 is a cross-sectional view taken along lines 6--6 of FIG. 2 to show
the reseau support structure and lighting components.
FIG. 7 is an enlarged view of the right side of the reseau support
apparatus and lighting components shown in FIG. 6 to illustrate the
lighting functions of the components of this invention.
FIG. 8 is an enlarged cross-sectional view of the grid groove shown in FIG.
7 along with a plot of light intensity associated with the grid structure;
FIG. 9 is an enlarged plan view of a computer image of the reseau grid of
FIG. 8 according to the present invention.
FIG. 10 is an enlarged cross-sectional view of the grid of an alternate
embodiment grid structure similar to that shown in FIG. 8 but modified to
achieve an alternate grid image effect.
FIG. 11 is an enlarged plan view of a computer image of the reseau grid of
FIG. 10 according to the present invention.
FIG. 12 is an enlarged cross-sectional view of still another alternate
embodiment ink-filled grid mark according to this invention.
FIG. 13 is a block diagram of an axis position controller of the present
invention;
FIG. 14 is a block diagram of the entire data information system of the
present invention; and
FIG. 15 is an enlarged fragmentary view of a corner of the reseau plate and
grid marks with an image frame shown at a home position and with an
alternate position image frame shown in broken lines and illustrating the
three coordinate systems of the present invention; and
FIG. 16 is a front elevation view of a CRT and cursor display of a
digitized image according to the present invention;
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 features 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 30 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 carraige 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 carraige assembly 100 within the
double Z-axis mounting structure 80 in such a manner that it 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 member 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, 43. 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 carraige 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 engaged 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 move rearwardly in the platform 50.
Referring now primarily to FIGS. 4 and 5, the double Z-axis mounting
structure 80 includes a camera carraige 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 110. 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 threadedly 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 lnes 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 patternon 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 162, 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 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 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 results 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 virtuallyno
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 into 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 | | |
