Television – Special applications – Observation of or from a specific location
Reexamination Certificate
1997-03-26
2001-10-30
Rao, Andy (Department: 2713)
Television
Special applications
Observation of or from a specific location
C348S140000, C348S141000
Reexamination Certificate
active
06310644
ABSTRACT:
FIELD
The present invention relates to an improved camera theodolite system for determining the three-dimensional coordinates of points on an object.
BACKGROUND
Theodolite measuring systems were originally confined to use for surveying in which two theodolites
10
and
12
mounted on stands
14
and
18
, respectively, as shown in
FIG. 1
were positioned a known distance apart which constituted the baseline and at known relative heights to each other. Each theodolite was then pointed at a point
22
in space of unknown coordinates and then, by using triangulation and the pointing angle of the theodolites relative to the baseline, the coordinates of the point would be determined. Commercial systems incorporated a computer
20
to measure the angles and control the pointing of the theodolites. Over the past few years such systems have begun to find industrial applications. However, all such systems require the relative positions of the theodolites to first be established by measurement and, during measurement, the object and the theodolites must be stable. Moreover, these systems can only measure one point at a time.
A laser rangefinder has been incorporated into a theodolite to make a station that can measure both the angle and distance to a target. Thus, a single station thus arranged provides all the functionality of a 3-D measuring system but still suffers from the drawbacks mentioned above.
Accordingly, it is an object of the invention to provide an improved theodolite measuring system. It is a further object of the invention to provide a theodolite measuring system that can establish coordinates in space without the need to make physical measurements to establish a baseline reference. It is a further object of the invention to provide a three dimensional coordinate measuring system that permits movement of the theodolites during measurement.
SUMMARY OF THE INVENTION
According to the invention there is provided a three-dimensional coordinate measuring system that includes a first and second towers, first and second camera assemblies mounted on first and second towers, respectively, and a pair of reference targets mounted on each of first and second towers a known distance apart. A tilt sensor is mounted on each of the first and second towers and measures the angle of each of the first and second towers with vertical. A host computer is coupled to each of camera assemblies and is programmed to perform photogrammetric algorithms so as to compute the coordinates of unknown points.
The first and second camera assemblies may each be a pair of cameras mounted on respective first and second towers in a fixed relationship to each other.
The reference targets may be illuminated from the rear. The cameras are preferably CCD cameras. Interface electronics on each tower may be coupled to respective tilt sensors and CCD cameras and to the host computer.
Advantageously the towers are mounted on casters.
Preferably, one of the cameras on each of the first and second towers may be positionable and operative to view the reference targets on the other of the first and second towers while the other camera on the one tower views an object whose coordinates are to be determined.
Object points may be measured using a hand held probe having a plurality of targets spaced in a geometric progression from a tip thereof.
The reference targets may be pulsed light emitting diodes emitting in the near infra red and said CCD cameras have near infra red optical bandpass filters thereon.
Advantageously the towers may be height adjustable.
The camera assemblies may also be a single camera and a beamsplitter. Such an arrangement avoids the need to introduce the inaccuracies from two cameras as opposed to those from just one for each tower.
In another aspect of the invention there is provided a method of measuring the three dimensional coordinates of an object in space which involves positioning two towers each having a camera assembly and a pair of reference targets, spaced a known distance apart, such that the camera assembly on each tower views the reference targets on another of said towers and the object. At least a portion of the image received by the camera assembly is digitized, transferred to a host computer which performs a triangulation calculation on the two viewing devices to determine the three dimensional coordinates of the object. Preferably the camera assembly on each tower is a pair of CCD cameras.
Advantageously, only the pixels from the CCD cameras having an amplitude in excess of a threshold above a ‘black level’ are transmitted to the host computer.
The cameras may be calibrated by measuring distortions in the image forming process and then constructing an analytical model to subsequently correct the images acquired in the future.
Field calibrating the cameras may be employed by using a redundant set of data to determine camera parameters prior to determining three dimensional coordinates of object.
REFERENCES:
patent: 4841460 (1989-06-01), Dewar et al.
patent: 4928175 (1990-05-01), Haggren
patent: 5285397 (1994-02-01), Heier et al.
patent: 5396331 (1995-03-01), Kitoh et al.
patent: 5440392 (1995-08-01), Pettersen et al.
patent: 5579102 (1996-11-01), Pratt et al.
patent: 5812247 (1998-09-01), Meyer
Proceedings of a workshop held as part of the American Society of Photogrammetry American Congress on Surveying & Mapping 1984 Fall Convention Sep. 9-14, 1984 entitled: Close-Range Photogrammetry & Surveying: State-of-the-Art Developing the Art of Application.
3DM Devices Inc.
Hall Priddy Myers & Vande Sande
Rao Andy
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