3D Point Cloud Colourisation via Parallax Correction
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Solution Overview
Problem
Existing surveying instruments face challenges in accurately colourising three-dimensional point clouds due to parallax errors caused by the off-axis placement of cameras, leading to incorrect colourisation, especially in regions where the camera and instrument have different perspectives.
Innovation Solution
An algorithm using 3D data and projective geometry is implemented to detect and correct parallax points by assigning colours based on adjacent points, allowing for correct colourisation of point clouds even when cameras are placed outside the nodal point, and using In-painting techniques to estimate colours from intensity and distance properties of reflected laser light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the camera is placed off-axis relative to the surveying instrument, then the device complexity and cost are reduced, but parallax errors occur causing incorrect colourisation of point clouds
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correspondence relationships between camera coordinates and instrument coordinates before actual point cloud processing. The system pre-identifies parallax-affected regions and pre-establishes correction mappings, so that during runtime, the colourisation process can directly apply corrections without real-time complex calculations, thus maintaining accuracy while simplifying the operational complexity
Solution Approach 2:
The patent introduces an intermediary coordinate transformation system that acts as a mediator between the camera coordinate system and the instrument coordinate system. By establishing a intermediate reference framework and using projective geometry transformations, the system bridges the parallax discrepancy between off-axis camera and instrument, enabling accurate colourisation without requiring the camera to be positioned at the instrument's optical center
2Measurement precision
If the camera is incorporated inside the laser scanner to achieve the same perspective, then colourisation accuracy is improved, but the device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent applies the copying principle by creating a virtual model of the instrument's perspective from the camera's off-axis position. Instead of physically relocating the camera to the instrument's optical center, the system captures images from the accessible off-axis position and uses computational methods to copy and transform the perspective, thereby achieving accurate colourisation while maintaining ease of manufacturing
Solution Approach 2:
The patent introduces coordinate transformation algorithms and projective geometry calculations as intermediaries that mediate between the physically separated camera and instrument coordinate systems. This intermediary computational layer eliminates the need for physical integration while maintaining measurement accuracy
3Measurement precision
If a camera is brought to the surveying instrument's position a posteriori, then colourisation accuracy is improved, but the process requires extra high precision components and increased complexity
Solution Approach 1:
The patent applies preliminary action by performing all necessary coordinate transformations, parallax corrections, and correspondence mappings during the data processing stage rather than requiring high-precision physical alignment during instrument assembly. The system pre-processes the relationship between camera and instrument coordinates, storing transformation parameters that can be applied during point cloud colourisation without requiring complex real-time calculations or high-precision mechanical components
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
This method enables accurate colourisation of point clouds without false colourisation, simplifies camera placement, and reduces the complexity and cost associated with aligning camera and surveying instrument perspectives, while maintaining high image quality and resolution.
Implementation Method 1
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
Implementation Method 2
Common surveying instruments comprise a unit for sending out a scanning beam and for receiving the reflected beam in order to measure the distance of a point the beam was directed at
Data Source
AI summary
A method for colourising a three-dimensional point cloud including surveying a point cloud with a surveying instrument. Each point of the point cloud may be characterised by coordinates within an instrument coordinate system having an instrument center. The method may include capturing a first image of the setting with a first camera. Each pixel value of the first image is assigned coordinates within a first camera coordinate system having a first projection center as origin and a first parallax shift relative to the instrument center. The method may include transforming the point cloud from the instrument coordinate system into the first camera coordinate system, resulting in a first transformed point cloud, detecting one or more uncovered points within the first transformed point cloud which are openly visible from the first projection center, and for each uncovered point, assigning a pixel value having corresponding coordinates in the first camera coordinate system.