Curved Deflecting Mirror Aligns Camera Pupil with Scanner Nodal Point
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Solution Overview
Problem
Existing laser scanning systems face challenges in achieving parallax-free image acquisition, leading to incorrect reference of image data to scanning data and missing color information due to parallax errors, which are complex and resource-intensive to correct.
Innovation Solution
A surveying device with a rotation unit featuring a curved deflecting surface, such as a hyperbolic mirror, is designed to align the camera's entrance pupil with the nodal point of the laser scanner, ensuring a parallax-free setup by defining the field of view through a specific orientation of the rotation body around the fast scanning axis, allowing for precise image acquisition without parallax errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the camera is incorporated inside the scanner with components arranged such that the camera and the scanner have the same optical axis, then the parallax error is reduced, but the entrance pupil location of the camera is not at the same location as the nodal point, so only the central point of the camera has the same perspective as the scanner while other points in the field of view still have parallax error
Solution Approach 1:
A virtual image of the camera's entrance pupil is created using a mirror or lens system, positioning it at the nodal point of the scanner. This intermediary optical element allows the camera's actual entrance pupil to be located separately while achieving parallax-free imaging by making the virtual entrance pupil coincide with the scanner's nodal point, thus resolving the contradiction between reducing parallax error and avoiding complex component arrangement
2Measurement precision
If a camera is a posteriori brought virtually into a position close to the position where the scanner had been to scan the environment, then some parallax error is reduced, but high processing effort is required and artefacts remain due to the relatively large parallax between entrance pupil of camera and nodal point of scanner
Solution Approach 1:
The optical system is pre-configured during device assembly to create a virtual image of the camera's entrance pupil at the scanner's nodal point before any scanning or imaging operations occur. This preliminary optical arrangement ensures that parallax errors are eliminated at the source, avoiding the need for complex post-processing corrections and reducing processing effort while maintaining high image reference accuracy
3Measurement precision
If algorithmic correction is implemented to identify and correct parallax regions, then some colorisation accuracy is improved, but the process is comparatively time-consuming and resource consuming
Solution Approach 1:
Instead of treating parallax error as a problem to be corrected through time-consuming algorithms, the optical system is designed to convert the geometric relationship between camera and scanner into a benefit by creating a virtual entrance pupil at the nodal point. This transforms the potential source of parallax errors into a parallax-free system, eliminating the need for corrective algorithms and significantly improving processing speed while maintaining high colorisation accuracy
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables high-precision image acquisition with complete color information, reducing artifacts in 3D point cloud data and improving the reliability of scan results by minimizing parallax effects, thus providing a quasi-parallax-free image capturing system.
Implementation Method 1
the rotation body comprises a curved deflecting element which provides defined deflection of an optical axis of a camera sensor
Implementation Method 2
the rotation body comprises at least one slanted scanning surface which comprises a scanning mirror which is arranged tilted relative to the scanning axis and provides defined deflection of the measuring light
Implementation Method 3
The distances may be calculated with the travel time measurement (time-of-flight) method by observing the time between sending out and receiving a signal
Data Source
AI summary
A surveying device including a base defining a base axis (A), a support structure defining a rotation axis (B), a light emitting unit, a light receiving unit detecting reflected measuring light, and a rotation unit including a rotation body including at least one scanning mirror arranged tilted relative to the rotation axis (B) and a curved deflecting element different from the scanning surface. The surveying device also includes an imaging unit including a camera sensor which is fixedly arranged so that an optical axis of the camera sensor is directed towards the rotation body, such that only in a predetermined imaging-alignment of the rotation body around the rotation axis (B) the optical axis of the at least one camera sensor is deflected by the curved deflecting element by a desired angle and direction so that the field of view comprises a defined field angle around the rotation axis (B).