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What PTB can do with a cow’s hide

Protecting the environment by measuring the surfaces of “natural objects”

PTBnews 3.2023
Especially interesting for

Dimensional metrology

Life sciences

PTB has determined the surface of a life-size cow model. This has enhanced the experience in the dimensional measurement of natural or near-natural material, which will be beneficial to future metrological challenges.

The cow model tagged with measurement dots is illuminated with a structured-light 3D scanner, and photographs are taken with a digital camera from many different positions.

Environmental protection issues are gaining in importance in metrology; physics is increasingly being faced with questions from the fields of biology and other life sciences, but these topics are not entirely new. For a long time, PTB has been verifying the accuracy of wood measuring systems used in industry within the framework of the Measures and Verification Act. As a reference procedure, PTB uses a modern 3D scanning system and special software that was developed in-house for this purpose.


This technology can also be applied to other biological materials. One of the challenges here is the irregular shape of the biological material. PTB has applied its experience with complex-shaped measurement objects within the scope of a special project: The measurement of a life-size model of a dairy cow made of glass fiber composite material for the Institute for Application Technology in Plant Protection of the Julius Kühn Institute in Braunschweig (JKI). The idea was to determine a calibrated target value for the surface. And the aim was to create a “reference cow” for experiments on the degree of wetting. As part of a research project with the Christian Albrechts University Kiel, the JKI intended to determine the tolerability of a new agent that could be sprayed in a cow shed in order to reduce ammonia emissions.

Meanwhile, the reference cow has been completed, and it is now in JKI’s experiment shed. Its surface measures 5.564 m2. To determine this value, adhesive dots were distributed over the surface. The metrological traceability was ensured by coded markings distributed around the surface and two calibrated scales. After that, some dozen photographs were taken from as many different positions as possible using a camera with a special lens. Based on the dot marks, mark crosses and scales recognized by the measuring software, these images were arranged on the screen true to the original. Then the actual digitalization of the surface followed by means of a high-accuracy structured-light 3D scanner. In a further step, the 3D scanner for lengths and diameters was traced (back) via calibrated reference objects. The measurement uncertainty was approximately 0.5 mm.

PTB has thus extended its experience in measuring objects with complicated shapes. This know-how can also be used for many other purposes. The measurement of much more irregular objects is thus also conceivable.