Terrestrial Laser Scanning With Dual Repetition Rate MTA Disambiguation
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Solution Overview
Problem
Existing terrestrial scanning instruments face challenges in resolving multiple-time-around (MTA) ambiguity due to high pulse repetition rates, where echoes from reflected pulses mix with transmitted pulses, especially in environments with distance jumps, leading to computational complexity and inefficiencies in disambiguation methods.
Innovation Solution
A terrestrial scanning instrument employs two pulse trains with different repetition rates, allowing for efficient MTA disambiguation by assigning acquisition events to transmission events based on the unique repetition rates, and utilizing anchor points to resolve ambiguity zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pulse repetition rates are used, then scanning productivity is improved, but MTA ambiguity increases making disambiguation more difficult
Solution Approach 1:
The patent segments the pulse train into multiple sub-pulses with different repetition rates. The first pulse train operates at a higher repetition rate for productivity, while the second pulse train operates at a lower repetition rate for easier disambiguation. This segmentation allows the system to handle MTA ambiguity by processing different pulse trains separately and then combining the results.
Solution Approach 2:
The patent employs periodic action by using two pulse trains with different periodicities (repetition rates). The first pulse train has a shorter period for high scanning speed, while the second pulse train has a longer period for reduced ambiguity. This periodic variation in pulse transmission enables the system to overcome the limitations of using a single fixed repetition rate.
2Speed
If high pulse repetition rates are used, then scanning speed is improved, but computational complexity for disambiguation increases
Solution Approach 1:
The patent divides the scanning system into two independent pulse train generators, each with its own evaluation unit. This segmentation reduces computational complexity by allowing parallel processing of disambiguation tasks for different pulse trains, rather than handling all pulses from a single high-rate train sequentially.
Solution Approach 2:
The patent applies partial action by using the second pulse train with lower repetition rate only when needed for disambiguation, rather than continuously operating at high rate. This selective approach reduces overall computational load while maintaining scanning speed through the first pulse train's high-rate operation.
3Device complexity
If single pulse train is used, then device complexity is reduced, but MTA ambiguity cannot be resolved in environments with distance jumps
Solution Approach 1:
The patent makes the scanning system multi-functional by enabling it to operate in two modes: high-speed scanning using the first pulse train, and ambiguity resolution using the second pulse train. The system can switch between these modes or use both simultaneously, making it universally applicable to various scanning scenarios including those with distance jumps.
Solution Approach 2:
The second pulse train acts as an intermediary that facilitates MTA disambiguation. It provides a reference framework with longer ambiguity zones that can resolve ambiguities in the first pulse train's shorter ambiguity zones, effectively mediating between the conflicting requirements of high speed and reliable disambiguation.
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 approach reduces computational complexity and enhances the efficiency of MTA disambiguation, providing accurate point cloud data with reduced computational demands and improved flexibility in handling environments with distance jumps.
Implementation Method 1
measuring a time of flight of an electromagnetic pulse, in particular a laser pulse, reflected from a plurality of object points in the environment
Implementation Method 2
light pulse source configured to generate a first pulse train comprising first scanning pulses at a first repetition rate
Implementation Method 3
acquire first scanning pulses of the first pulse train and second scanning pulses of the second pulse train reflected from object points in the environment
Implementation Method 4
a reflected pulse from a particular transmitted pulse may arrive at the detector
Data Source
Figure 1a~1b
Figure 1c~1d
Figure 2a~2b
AI summary
A terrestrial multiple-time-around, MTA, scanner (10) for providing a point cloud comprises: a light pulse source for generating pulse trains comprising scanning pulses with corresponding repetition rate; a transmission unit to transmit the first scanning pulses and the second scanning pulses respective transmission directions, the transmission unit comprising a beam deflection element, angle sensors and elements for providing respective transmission times; an acquisition unit to acquire scanning pulses of the pulse train reflected from object points in the environment; and an evaluation unit to assign the acquisition events to the respective transmission events based on an MTA disambiguation. The scanning instrument carries out a scanning process comprising: (a) in a first circle (21), rotating the transmission direction with a first rotation speed and generating and transmitting scanning pulses of a first pulse train with a first repetition rate; and (b) in a second circle (20), rotating the transmission direction with a second rotation speed and generating and transmitting scanning pulses of a second pulse train with a second repetition rate. The second repetition rate is different from the first repetition rate. First (211) and second (221) circle object points provide information from essentially the same area representing a topography of an object (3). First (241) and second (242) tilting rotation speeds around a tilting (elevation) axis (24) are orders of magnitude faster than respective bearing rotation speeds (341, 342) about a bearing (azimuth) axis (34). Rotation directions in the first (211) and second (221) circles may be opposite.