铁路应用避免碰撞量计算

To detect potential collision, 3D laser scanning is considered the best-in-class approach as it delivers a complete and accurate 3D representation of the entire tunnel. After scanning and preparing data, the first step will be to extract the rails from the scan data. There are several ways to do it, from manual operations to automated workflows assisted by software.

铁轨的提取精度至关重要，并且在很大程度上依赖于点云的准确性和密度，该云由所选的3D laser scanner. Automation requires data density and consistency, thus, noisy or low-density point clouds will make the automation process impossible. In this data sample, theLeica Pegasus:Two Ultimatewas used because a main advantage of this mobile mapping system is that it provides both accuracy and density throughout the entire tunnel as it moves and captures data.

这种分析的另一个重要因素是铁路运营商希望在隧道中允许未来交通的运输条件的尺寸。运输尺寸数据通常作为横截面传递

Based on these input data (the point cloud, the rail track and the carriage section), the objective is to identify if any material would collide while a train is going through the tunnel.

Standard approach
标准方法包括沿轨道挤出截面。此过程在任何CAD软件中都非常熟悉。它包括定期沿导轨移动该截面（上图中的绿色），并将每个部分与前面的部分连接起来以获得挤出的表面。

只要铁轨是笔直的，这种方法就足以确定沿轨道移动所需的体积。

此方法本地可用Leica Cyclone 3DRthanks to the “Extrusion along a path” feature.

The potential collisions between the point cloud of the environment and the surface envelope of the carriage can be automatically identified in Cyclone 3DR. The method consists of splitting the point cloud in two set of points:

• The points not colliding with the envelope are the ones far from the envelope

• The points colliding with the envelope are the ones inside or close to the envelope

Advanced approach
To deliver a more relevant output suitable for rail lines with more complex geometries, it is necessary to take into account the radius of the rails, and use the hypothesis according to which the carriage does not deform when moving along the rails. This requires a more advanced approach that consists of moving the carriage along the rails at different kilometric points. At a given kilometric point, all wheels need to fit onto the rail, thus the position and orientation of a carriage are completely defined by this complex requirement.

下面在理论条件下评估了高级方法，夸大了现实生活条件，以便更容易地可视化差异。

The position of the carriage at a given kilometric point is shown in the image below. In this theoretic dataset, the following assumptions were made:

• The radius of the rails is 100m

• The length of the carriage is 50m

• 车轮位于末端的5m处

In the image below, we can see that more space is required inside the curve, but also outside of the curve because of the 5-metre distance between the wheel and the carriage extremities.

一旦在每个必需的公里点计算了马车的位置，下一步就是计算一个布尔操作，总结每个马车。

为了减少处理时间,我的布尔运算s performed here in 2D at different kilometric positions. The Boolean operation are illustrated in the image below, the blue lines illustrate the position of the carriage at each kilometric point while the green line sums up the necessary tunnel shape to accommodate the carriage. This advanced approach was implemented inside Cyclone 3DR using the scripting functions available through the JavaScript API.

两种方法之间的区别
As one can expect, the difference between the two approaches is null in the case of straight rails.

但是，轨道弯曲的越多，先进的方法对防止严重的错误计算至关重要，从而导致项目延迟甚至损坏的设备。对于上面的配置，差异如下图所示。蓝线对应于用简单方法计算的所需卷，其中绿色的卷与用高级方法计算的所需卷相对应。很明显，简单的挤出方法大大低估了所需的空间。

In order to give an idea about how much the required volume is under-estimated depending on the rail curvature, different configurations were tested and the differences between the two approaches inside the curve are reported in the graph below. The graph shows that, for a 50m carriage with its wheels located 5m from the carriage extremities, a rail radius of 1000m makes the simple approach off by 20cm. And even for a larger rail radius of 2500m, the difference is still greater than 5cm.

Real-life data
The theoretical carriage and tunnel discussed above offer an exaggerated example to demonstrate the dramatic impact that the advanced approach can have on the final results of an analysis, however, even in moderated, real-life conditions, the impacts can be seen clearly.

Both approaches were compared at an active project site where the local radius of the rail was 600-meters and the carriage considered in this real-life use case was 50-metres. The tunnel was scanned using aLeica Pegasus:Two Ultimate. The rails were extracted directly on the point cloud with millimeter accuracy.

The images below show the difference between the results from the two approaches and compare each result against the tunnel’s point cloud.

The points in red below were automatically detected as colliding with the surface envelope created with the advanced approach. This is where rework is necessary.

很明显，这里可以看到简单方法的结果表明，目标马车可以通过该隧道。当使用更高级的方法时，马车清楚地与隧道墙碰撞，这意味着要使托架拟合穿过隧道。

Conclusion
There are valuable use cases for both the simple and advanced methods of carriage clearance calculations. In cases where rail lines are straight and regular, the simple approach will allow users to make decisions rapidly with minimum effort and time, however in scenarios where the rail lines or tunnel walls are less regular, the time spent in pursuing the advanced approach will ensure that a miscalculation does not delay a project, or worse, damage equipment or the tunnel walls.

得益于专门针对3D点云和3D网格处理的多功能且完整的JavaScript API，Cyclone 3DR提供了一种强大的方法来创建针对特定应用程序量身定制的高级分析，从而使其在行业内独特。

试一试自己的数据
实现高级方法的脚本可作为Cyclone 3DR 2021.1.2中的最爱脚本获得。

Gilles Monnier
General Manager, Technodigit
Reality Capture Division