当每毫米计数

Author:塔玛斯·萨法尔（Tamas Safar）

When thinking of common laser scanning applications, capturing intricate 3D objects or structures comes to mind. Flat, dark surfaces, just like the asphalt of the Zalaegerszeg test track in western Hungary, do not escape, however, the realm of High Definition Surveying (HDS). A 3D smart digital reality of this unique proving ground was created to ensure the track offers driving stability not only for conventional automobiles, but also for autonomous vehicles and electric vehicles.

With the Zalaegerszeg Automotive Proving Ground, Hungary provides an unparalleled venue with the highest standards. The world’s leading automotive companies, research teams and universities, will test here from breaking systems, running gears and tires to onboard navigation systems; as well as testing self-driving vehicles in an especially urban-built environment.

HDS professionals from Hírös Geo Kft assessed the quality of the pavement structure and flatness by analysing 3D point clouds generated by laser scanning.

Point clouds for pavement

Engineering teams need to produce the best possible quality pavement with an even surface so teams can trial automobiles. The dynamic platform is the area of the test track system where the cornering grip/slip friction and overturning stability of the self-driving vehicles incoming at high speed will be tested. Hírös Geo Kft, a Hungarian land surveying, engineering and utility geodesy company, was commissioned for the quality control of the 10 centimetres thick asphalt base layer of the 300-metre diameter circular dynamic platform.

The accuracy requirement was very strict – Hírös Geo Kft needed proof that the top surface of the asphalt base layer deviated only few millimetres relative to the planned plane surface at any of its tested points.

Hírös Geo Kft chose terrestrial laser scanning to measure the asphalt deviation. The specialists carrying out the measurement presented the divergences from the measured surface in the nodes of a regular 2 cm x 2 cm grid covering the dynamic platform. All measurements fitted to the Hungarian Unified National Projection measuring coordinate system.

使用Leica扫描仪P40，该地区的详细调查包括70,650平方米，度过了整个工作日。单个设置产生的高质量数据，对应于计划的采样密度，在激光扫描仪周围40米的半径内。通过使用Traverse测量方法收集48个设置并链接。这导致了大约3D点云3.45 billion measure points。Point clouds were evaluated in the Leica Cyclone REGISTER software after a basic cleaning process.

“通过传统的测量技术进行控制测量是不可能的。ScanStation P40为我们提供了自由和灵活性，可以生成所需的数据数量，直接缩放到项目要求，”said Barna Bodri surveying specialist at Hírös Geo Kft.

像皮带一样平坦

设置的高精度注册也许是最大的挑战。由于沥青是单调的，平坦的，深色的表面，没有任何方向，因此无法通过3D点云后处理软件对“相同表面”（自动对准和视觉对齐）的识别来帮助该过程。相反，地面控制点上方的黑白目标使注册能够在全球上accurate to 1.8 mm。

The evaluated data clearly revealed that the upper surface of the asphalt layer has a match of nearly 90 per cent, provided that the deviation of the measured points cannot be greater than a few millimetres to the best fit plane. To lay the asphalt layers, operators relied on the Leica iCON iGG3 to guide the grader with precise control of the blade. Thanks to the 3D coordinates, it was easy to define and stake out in the field which areas need milling before the binding layer was placed. From here, the milling is an easy process using automated iCON machine control.

What caught the eye of experts at the Hungarian civil engineering company in charge of building the automotive proving ground was the presence of indirect signs of strip-like elongations, parallel to the direction of the travel, of the areas outside the specified tolerance exactly where the edges of the asphalt tracks meet. Protruding surfaces are related to the temperature of the asphalt when spread – an asphalt track already laid is in the cooling phase when the connecting strip is deposited at elevated temperatures. The higher the difference in temperature between the joining surfaces, the more difficult it is for the road roller to smoothen the connection.

创建数字现实

Reality capture allowed HDS experts in Hungary to measure and verify the surface uniformity with a 3D georeferenced model, optimising the construction workflows and digitally sharing information between the field and office.

Based on the presented useful information, expertsoptimised their workflows and reduced the required time and coststo achieve quality work most effectively.