3D Mode-Shape Extraction Through Event-Based Light Fields
摘要
Extracting 3D mode-shapes from vibrating structures in the field presents a number of challenges; accelerometers attached to a structure provide full 3D motion at high temporal resolution but cannot match the spatial resolution of conventional 2D imagers (both logistically by cost and practically by weight). Furthermore, installation costs associated with contact-sensors can be very high. Conventional 2D imagers have higher spatial resolution, but for wide area monitoring, perspective projection lenses must be used. The use of perspective projection results in spatial ambiguities which complicates extracting 3D geometry information from the scene. Time-of-flight imagers return 2D surfaces in 3D space but have lower frame-rates than conventional high-speed cameras. All three devices traditionally poll scenes at a uniform rate regardless of whether the scene is static, both consuming power unnecessarily and generating redundant data, warranting either post-processing or extended storage space. We propose a fusion between silicon retina event-based neuromorphic imagers and light field imager architectures to capture an ‘event-field.’ Event-based imagers differ from conventional frame-based cameras in that they do not capture frames and instead only report information for pixels at which the intensity value change exceeds a set threshold. As a result, event-based imagers tend to effectively sample the scene in an efficient manner that naturally adapts to the spatiotemporal scales observed in the field of view. Because the rate of events generated by the silicon retina varies proportional to the spatiotemporal frequency of dynamics within the observed scene, it consumes less power and generates less data than a conventional 2D imager operating at an equivalent spatial and temporal resolution. By using an array of silicon retina imagers (or micro-lens array fitted to a single silicon retina), it is possible to obtain an approximation of the depth in post-processing. Additional benefits of the silicon-retina light field imager include a larger dynamic range than conventional cameras, the ability to apply digital coded exposure, shift focus, and building stacked-focused images in post-processing. We demonstrate the utility of event-based light field imagers for structural dynamics applications, particularly those that feature constraints on power and memory while simultaneously needing to capture structural vibrations.