UAV Stereo Vision Altitude Calibration Beyond Baseline Limits
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Solution Overview
Problem
Existing altitude sensing technologies for unmanned aerial vehicles (UAVs) face limitations in accuracy and operational range, with barometric altimeters failing to account for terrain topography and stereo vision devices having limited maximum measurable altitudes due to size constraints and sensitivity to camera alignment.
Innovation Solution
A method that calibrates a stereo vision device using altitude values derived from both the stereo vision system and another device, such as a barometric altimeter, during ascent, allowing for accurate altitude readings beyond the usual range by creating a calibration table or graph, which can be used to adjust and compensate for changes in camera alignment and terrain variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a stereo vision device is used to determine altitude above ground level, then measurement precision is improved, but device complexity increases and maximum measurable altitude is limited
Solution Approach 1:
The patent uses a barometric altimeter as an intermediary device to provide reference altitude data during the calibration process. This mediator allows the stereo vision device to be calibrated against known altitude values, enabling the stereo system to achieve high measurement precision without requiring complex hardware modifications. The barometric altimeter serves as a bridge between the known physical altitude and the stereo vision measurements.
Solution Approach 2:
The patent changes the operational parameters of the stereo vision device by performing calibration at multiple different altitudes. By collecting stereo vision data and corresponding barometric altitude measurements across a range of altitudes, the system creates a calibration curve that allows the stereo device to maintain high measurement precision throughout its operational range, effectively extending its useful measurement capability.
2Measurement precision
If the separation distance between imaging devices in a stereo vision device is increased, then maximum measurable altitude is improved, but device complexity and size increase
Solution Approach 1:
The patent applies preliminary calibration action to compensate for the limited baseline length. By pre-calibrating the stereo vision device at multiple altitudes using reference barometric measurements, the system compensates for the small separation distance between imaging devices. This preliminary calibration establishes a relationship between stereo disparity and actual altitude that accounts for the limited baseline, enabling accurate measurements despite the small physical separation.
Solution Approach 2:
The patent changes the calibration parameters by performing measurements at multiple different altitudes rather than relying solely on the geometric parameters of the stereo device. This approach transforms the limitation of small baseline length into a manageable calibration issue, where the system learns the altitude-disparity relationship empirically across the operational range, effectively extending the measurable altitude range beyond what would be expected from the small physical separation.
3Ease of operation
If barometric altimeter is used to determine altitude, then ease of operation is improved, but measurement precision deteriorates due to terrain topography variations
Solution Approach 1:
The patent implements feedback by using the barometric altimeter to provide reference altitude measurements during the calibration process. The stereo vision device measurements are compared against the barometric reference, and this feedback loop allows the system to learn and compensate for barometric errors specific to the operating environment. The calibration data collected at multiple altitudes captures the relationship between barometric readings and actual altitude, enabling the system to correct for terrain-induced barometric variations.
Solution Approach 2:
The patent uses the stereo vision device as an intermediary to bridge the gap between barometric altitude measurements and actual geometric altitude. During calibration, the stereo vision system provides independent geometric measurements that serve as a reference truth, allowing the system to identify and compensate for barometric altimeter errors caused by terrain topography. This intermediary approach maintains the ease of operation of barometric sensing while correcting its precision limitations.
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
The present invention relates to a method for calibrating an altitude sensing stereo vision device (122) of an unmanned aerial vehicle (100), wherein the method comprises: arranging the unmanned aerial vehicle to take off from ground (G) and ascend; deriving at least one first altitude value (10a-15a) from the stereo vision device and obtaining at least one corresponding second altitude value (10b-15b) from another device (123) of the unmanned aerial vehicle during the ascent (1) of the unmanned aerial vehicle; recording the derived at least one first altitude value and the obtained at least one corresponding second altitude value as calibration data; deriving an additional first altitude value from the stereo vision device while the unmanned aerial vehicle flies a route; determining a second altitude value corresponding to the derived additional first altitude value based on the recorded calibration data; and adjusting the derived additional first altitude value based on the determined second altitude value.