Particle image velocimetry (PIV), or digital image correlation (DIC), is a widely used technique to measure soil displacements and strains in small‐scale geotechnical models. Arrays of single‐board computers (SBCs) produced by Raspberry Pi, and their associated 8‐MP cameras, are being used at the University of Cambridge to capture the images required for DIC analysis. This alternative to more expensive camera set‐ups has numerous advantages. A single expensive and large camera can be replaced—at low cost—by multiple cameras, adding flexibility and affordability to any experimental set‐up. Traditionally, the alignment of multiple cameras to each other and the referencing to a known coordinate system required painted or machined markers to be located on the observation windows through which the experiments are viewed. This can obstruct localised soil grain displacement measurements in those areas of the model where such markers are placed. To complement the Raspberry Pi camera system, a markerless calibration method was used during image acquisition. This paper outlines the set‐up of four of these small computers and associated cameras, provides an overview of the use of the markerless referencing system and reviews two different experimental apparatus used to measure soil displacement and strain. When the cost of additional cabling, connectors and mounting hardware is considered for this system, the total cost to implement was approximately $125 USD per camera plus one‐time costs of $175 USD for system peripherals, which represents outstanding value and enables practically all geotechnical laboratories to develop similar capabilities.

中文翻译：

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用于岩土工程的低成本数字图像相关和应变测量

粒子图像测速（PIV）或数字图像相关（DIC）是一种在小规模岩土模型中测量土壤位移和应变的广泛使用的技术。剑桥大学正在使用由Raspberry Pi生产的单板计算机（SBC）阵列及其关联的8-MP相机来捕获DIC分析所需的图像。这种替代更昂贵的相机设置的方法具有许多优点。一台昂贵的大型摄像机可以用多个摄像机以低成本替换，从而为任何实验设置增加了灵活性和负担能力。传统上，多个摄像机相互对准并参考已知的坐标系，需要将涂漆或加工过的标记置于观察窗口，通过观察窗口可以观察实验。这会妨碍在放置此类标记的模型区域中进行局部土壤颗粒位移测量。为了补充Raspberry Pi相机系统，在图像采集过程中使用了无标记的校准方法。本文概述了其中四个小型计算机和相关相机的设置，概述了无标记参照系统的使用，并回顾了用于测量土壤位移和应变的两种不同的实验设备。考虑到此系统的额外布线，连接器和安装硬件的成本，每台摄像机的实施总成本约为125美元，加上系统外围设备的一次性成本为175美元，这代表了卓越的价值，几乎使所有岩土实验室都能投入使用发展类似的能力。