A Guide to Extracting Railroad Tracks From Lidar

Accurately mapping railroad corridors is essential for reliable maintenance, structural planning, and effective change detection. With Global Mapper Pro’s collection of point cloud processing, terrain analysis, and automated breakline extraction tools, railroad analysis becomes efficient and approachable—whether your data comes from a drone survey or an existing digital elevation model (DEM).

Data Requirements For Railroad Analysis

To run a rail feature extraction workflow, you’ll need a high-resolution DEM. If you don’t already have a terrain model, you can generate one from a point cloud or even produce a point cloud from drone-collected imagery using Pixels to Points. If you’re looking to build or refine your photogrammetry workflow, explore our self-guided training and additional resources.

Preparing Your Point Cloud

When starting from a point cloud, the first step is to create a DEM using the Elevation Grid tool. Before beginning the gridding process, it helps to crop and classify the data to reduce processing time and simplify the workflow. 

Because this workflow focuses solely on the rail lines, the surrounding areas can be removed. To crop your data, open the Digitizer Toolset and draw an area feature around the rails. Then select that new feature and use the Crop to Selected Areas tool. 

If you prefer not to crop the data but still want to limit processing, many tools used in this workflow include a Bounds tab that allows you to restrict operations to a defined area.

To further clean up a point cloud, it is recommended to classify the ground points to exclude unnecessary objects such as trees, buildings, or noise. It is important to ensure that the rails are marked as ground and not excluded from the classification process. 

From Lidar to DEM

Once the point cloud is cropped and classified, use the Create Elevation Grid tool to generate the DEM needed for breakline extraction. This produces a continuous surface that the breakline tool evaluates for slope and elevation changes to identify rail lines. Keep in mind that the breakline tool works only with a surface model, not a mesh. In this dialog, the point cloud can be filtered by classification so only ground points are used. While optional, this typically results in a cleaner reference surface. 

In order for the remainder of the workflow to function correctly, the base data must be high-resolution enough for the rails to appear as a distinct elevation signature, see the images below for reference. Use the Path Profile tool to verify that the grid adequately represents that elevation change.

Rail Extraction

The Generate Breaklines tool offers three extraction methods, including options for identifying the edges of flat surfaces or areas with uniform slopes. For this railroad analysis, the focus is on: Find Breaklines at Any Surface Break. This method identifies breaklines along curvature changes based on the selected grid type. In the Breakline Setup dialog: 

1. Curvature Grid Type: Profile – Produces lines that run parallel to the rails. 
2. Edge Detect Threshold: ~500 – Controls how steep a slope must be for extraction. Moving the threshold slider far to the right helps isolate the sharp, nearly vertical edges characteristic of rails.
3. Edge Connect Threshold: <300 – Influences how the tool handles small inconsistencies. Lower values result in longer, more continuous breaklines.

Troubleshooting Breaklines

If the extracted rail breaklines appear fragmented or incomplete, try creating a Curvature Grid to test and visualize your settings. The breakline workflow relies on a curvature grid derived from your elevation data, so generating one directly can help you understand how grid resolution and method affect the results.

Try producing grids at different resolutions—for example, a 1-meter grid and then a 0.1-meter grid—and compare the output. You should be able to discern the rails clearly in the black-and-white curvature display. If no features are able to be discerned through what looks like TV static, adjust your curvature and breakline parameters.

Finally, verify that the underlying elevation grid has sufficient resolution for the rails to appear as distinct features; without that detail, breakline extraction will remain unreliable.

Extracting rail breaklines from elevation data is a powerful way to enhance accuracy in railroad analysis, maintenance planning, and change detection. By preparing a clean point cloud, generating a high-resolution DEM, and fine-tuning the breakline settings, you can reliably model and extract rail features. 

Global Mapper Pro streamlines each step of this workflow, making it accessible and dependable whether you’re working from drone-derived imagery, lidar point clouds or existing elevation data. Try integrating Global Mapper Pro into your workflow today.