Single Camera Height Estimation Using Projected Shadow Geometry
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Solution Overview
Problem
Existing methods for determining the positional or motional information of an object with respect to a reference surface using a single camera are inadequate, as they fail to provide unambiguous estimation of the object's height due to similar shadow sizes produced by objects of different heights.
Innovation Solution
An optical method utilizing a projector and a camera, where a structured-light pattern is projected onto the reference surface, and the camera captures images to generate a surface map and profile, allowing for the estimation of the object's height and positional information by analyzing the shadow length and projector-camera distances, even when the reference surface is non-flat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single camera is used to estimate object height from shadow size, then device complexity is reduced, but measurement precision deteriorates because objects of different heights produce similar shadow sizes
Solution Approach 1:
The patent transitions from 2D shadow size measurement to 3D height measurement by introducing the relationship between shadow length and object height through geometric projection principles. The system uses the camera-observable shadow length along with projector-camera geometry to calculate object height, effectively adding a dimensional transformation from planar shadow measurement to spatial height determination.
Solution Approach 2:
The patent changes the measurement parameter from direct shadow size to camera-observable shadow length, and introduces additional parameters such as projector-to-surface distance, camera-to-surface distance, and shadow-projector distance. These parameter transformations enable unique determination of object height that was not possible with simple shadow size alone.
2Ease of operation
If shadow size alone is used to determine object height, then measurement process is simplified, but reliability deteriorates due to non-unique solutions for objects at different heights
Solution Approach 1:
The patent introduces the shadow length along the topographical surface line as an intermediary measurement that connects the shadow observation to the object height. This intermediary parameter, combined with the projector-camera geometry, serves as a bridge that enables reliable height determination without requiring complex multi-camera systems.
Solution Approach 2:
The patent replaces the mechanical approach of using multiple cameras for 3D measurement with an optical-geometric approach using shadow analysis and projector-camera positioning. This substitution maintains measurement reliability while simplifying the system architecture by using light and geometry instead of additional mechanical sensing devices.
3Measurement precision
If multiple cameras are used to achieve unambiguous height estimation, then measurement precision improves, but device complexity and cost increase
Solution Approach 1:
The patent enables the single camera system to determine object height by utilizing the existing shadow information and projector-camera geometry relationship. The system serves itself by using the same camera that captures the shadow to also perform the height calculation through geometric relationships, eliminating the need for additional cameras while maintaining measurement precision.
Solution Approach 2:
The patent makes the single camera perform multiple functions: capturing the shadow for size estimation and simultaneously providing the geometric basis for height determination through its positioning relative to the projector and surface. This multi-functionality allows one camera to replace what would traditionally require multiple cameras.
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 unique determination of the object's height and positional information, including whether it touches the surface, and generates a time sequence of 3D coordinates for motional information like velocity and acceleration, using a single camera without the need for multiple cameras.
Implementation Method 1
A projector and a camera are used in the disclosed optical method. The projector and the camera are arranged such that when the object not touching the reference surface is illuminated by the projector
Implementation Method 2
a part of the object's shadow formed on the reference surface along a topographical surface line is observable by the camera, the aforesaid part of the shadow having a length being usable for uniquely determining the object's height above the reference surface
Data Source
AI summary
A method for receiving user inputs in a system comprising a projector and a camera is provided. The method is based on determining an object's height above a reference surface. A surface map is used for mapping a location on the reference surface and a corresponding location in a camera-captured image having a view of the reference surface. In particular, a camera-observed shadow length, i.e. a length of the object's shadow observable by the camera, estimated by using the surface map, is used to compute the object's height above the reference surface (a Z coordinate). Whether or not the object touches the reference surface is also obtainable. After an XY coordinate is estimated, a 3D coordinate of the object is obtained. By computing a time sequence of 3D coordinates, the motional information, such as velocity and acceleration, is obtainable.