Collision volume avoidance computation for rail application

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：两个终极was 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.

Another essential factor for such an analysis is the dimensions of the carriage that the rail operator wants to allow in the tunnel for future traffic. The carriage dimension data is usually delivered as a cross-section where both right and left wheels’ contact points are defined as well as the carriage width and height

基于这些输入数据（点云，铁轨和马车部分），目的是确定火车穿过隧道时是否有任何材料碰撞。

标准方法
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。

This approach is sufficient to ascertain the volume necessary for such a carriage to move along the rail, as long as the rail is straight.

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
为了提供更相关的输出，适用于具有更复杂几何形状的铁路线，有必要考虑到轨道的半径，并使用该假设，根据该假设，沿着轨道时行驶时车辆不会变形。这需要一种更高级的方法，包括在不同的千摩尔点沿着导轨移动马车。在给定的千学点，所有车轮都需要适合轨道上，因此，这项复合物的需求完全定义了马车的位置和方向。

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:

• 导轨的半径为100m

• The length of the carriage is 50m

• The wheels are located at 5m to the carriage extremity

在下图中，我们可以看到曲线内部需要更多空间，但由于车轮和托架肢之间的距离为5米，因此在曲线外部需要更多空间。

Once the carriage’s positions are calculated at each required kilometric point, the next step is to compute a Boolean operation that sums up each carriage.

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.

However, the more the rail is curved, the more the advanced approach is essential to prevent a critical miscalculation that can result in project delays or even damaged equipment. For the configuration above, the differences are shown in the images below. The blue lines correspond to the required volume calculated with the simple approach, where the green ones correspond to the required volume calculated with the advanced approach. It is clear to see that the simple extrusion approach is significantly under-estimating the required space.

为了了解所需量的数量根据导轨曲率的数量低估了，测试了不同的配置，并在下图中报告了曲线内两种方法之间的差异。该图显示，对于距车轮距离末端5m的50m托架，轨道半径为1000m，使该简单的接近20厘米。即使对于较大的轨道半径为2500m，差异仍然大于5cm。

现实生活数据
上面讨论的理论运输和隧道提供了一个夸张的例子，以证明先进方法可以对分析的最终结果产生巨大影响，但是，即使在适度的现实生活中，这些影响也可以清楚地看到。

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：两个终极. The rails were extracted directly on the point cloud with millimeter accuracy.

下图显示了两种方法的结果之间的差异，并将每个结果与隧道的点云进行比较。

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.

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
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.

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
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