3D scanning and 3D measurement - corner technology
2019-06-01
3D scanning and 3D measurement - corner technology
2014-01-25
technical background
Three-dimensional scanning technology was born to solve the design and manufacturing needs of the industrial field. Its mainstream technology can be roughly divided into the following four generations from the present to the present.
The first generation was a contact measurement technique that used a probe to make a contact measurement of the surface of the object. The representative product is a coordinate measuring machine, commonly known as a dot machine.
The second generation is a line laser scanning technology, which projects a laser line onto the surface of the object and then shoots it with a camera with a certain off-angle. The laser line in the image is bent by the shape of the surface of the object, thereby calculating the three-dimensional data. . The representative product is a laser 3D scanner.
The third generation is structured light scanning technology, which projects a specific set of light patterns onto the surface of the object, and then shoots it with a camera with a certain off angle, and thus calculates three-dimensional data. The most commonly used pattern is black and white stripes. This technology is currently the mainstream technology in China, and the corresponding products are commonly known as white light camera scanners.
The fourth generation is a hand-held scanning technology that uses a line laser to acquire a point cloud on the surface of the object and visual markers to determine the spatial position of the scanner during operation. Handheld scanning has the advantages of flexibility, efficiency, and ease of use, representing the future direction of development.
The first-generation and second-generation technologies are currently used only in some very high-end and professional fields due to their inefficiency, high cost, difficulty in use and maintenance. They are niche products and have a narrower market.
Compared with the previous two generations, the third generation technology has improved significantly in terms of efficiency, cost and use, and has therefore been promoted worldwide. However, with the further improvement of the requirements of the efficiency and ease of use of 3D scanning, the inherent defects of the technology have become obsolete, which has led to the fourth generation of 3D scanning technology - handheld 3D scanning.
Handheld scanning has maximum flexibility, but since the movement of the hand is arbitrary, how to accurately and in real time determine the spatial position of the hand at any time becomes the core issue of the technology. Spatial positioning technology based on visual marker points is the key to solving this problem. At present, there are only two companies in the world, one is us and the other is Canada's Creaform.
Technical advantages
Creaform's handheld scanner HandyScan series uses traditional dot markers for visual positioning. Since visual positioning requires an "ideal point" - that is, no size, the center of the circle is actually used, and the coordinates of the center of the circle are fitted by extracting the boundary of the circle. However, due to the existence of perspective projection and lens distortion, the boundary of the dot in the image is not a circle, nor an ellipse, but an irregular free shape, so there must be a deviation between the fitted center and the true center.
Unlike Creaform, we have abandoned traditional dot markers and used a new visual marker that does not cause bias - corner markers. Corner points are similar to black and white chessThe intersection of the grid, which meets the "ideal point" requirement - that is, no size. When extracting, we get the coordinates of the corner point directly, instead of getting it by fitting, so there is no deviation from the real corner point. This not only improves the positioning accuracy, but also ensures the accuracy and reliability of subsequent photogrammetry.
Corner technology for automotive crash testing
Corner technology is also used for automotive crash safety testing due to its high precision and reliability.
Car crash test
Compared with dot markers, the extraction of corner markers is much more complicated. If it is implemented by software alone, it is difficult to achieve real-time smooth scanning. To this end, we have incorporated the corner extraction algorithm into the hardware chip, which not only ensures the smoothness of scanning, but also greatly reduces the requirements for computer configuration. Our handheld scanner works fine with a normal computer. The interface used is a USB interface. See the computer configuration for details. Creaform's handheld scanners use software for visual positioning calculations, so the requirements for computer configuration are high, and the 1394 interface must be used to meet the transmission of large amounts of data.
