铁路应用避免碰撞量计算

When renovating train tunnels, checking the clearance is one of the top-priority matters to prevent any collision between trains and tunnel equipment

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.

The rail’s extraction accuracy is essential and heavily relies on the accuracy and density of the point cloud, produced by the chosen3D 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 Ultimate之所以使用，是因为此移动映射系统的主要优点是，它在移动和捕获数据时提供了整个隧道的精度和密度。

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
A standard approach consists of extruding the section along the rail. This process is very familiar in any CAD software. It consists of moving the section along the rail at regular intervals (in green in the image above) and connecting each section with the previous one to obtain the surface of the extrusion.

只要铁轨是笔直的，这种方法就足以确定这种马车沿导轨移动所需的体积。

This method is natively available inLeica 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.

The advanced approach is evaluated below in theoretic conditions, exaggerated to real life conditions so that the differences can be more easily visualised.

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
The wheels are located at 5m to the carriage extremity

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。

To reduce processing time, the Boolean operation is 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.

Difference between the two approaches
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
理论的马车和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.

下面的红色点会自动检测到与与高级进近产生的表面信封相撞的。这是需要返工的地方。

It’s clear to see here that on the results of the simple approach suggest that the target carriage can go through this tunnel. Whereas the carriage clearly collides with the tunnel walls when using the more advanced approach, meaning that additional work would be required to let the carriage fit through the tunnel.

Conclusion
对于运输清除计算的简单和高级方法，都有有价值的用例。如果铁路线直接且规则，那么简单的方法将使用户能够以最少的精力和时间迅速做出决定，但是在铁路线或隧道墙较少规则的情况下，追求高级方法所花费的时间将确保错误估计不会延迟项目，或者更糟的是损坏设备或隧道墙。

Thanks to a versatile and complete JavaScript API dedicated to 3D point cloud and 3D mesh processing, Cyclone 3DR offers a powerful way to create advanced analysis tailored to a specific application, making it unique within the industry.

Give it a try on your own data
The script implementing the advanced approach is available as a favorite script in Cyclone 3DR 2021.1.2.