Roads and Railroads
The tools for processing data of roads and railroads have been developed a lot since more and more data became available from Mobile Mapping System (MMS) surveys. This development is still ongoing, so there will be additions and improvements for the tool sets in the future.
Most of the tools are intended to be used with dense point clouds of high positional accuracy. Such point clouds are usually produced by Mobile Laser Scanning (MLS) systems. However, some of the tool described in this Chapter are applicable to Airborne Laser Scanning (ALS) point clouds as well. Some tools benefit from images which are collected by one or several cameras as part of a modern MMS or ALS system.
The processing of point clouds from MLS systems is a complex task if a high accuracy and quality for the end products shall be achieved. This includes the calibration of the scanner system, the matching of drive paths, the classification of the points into classes that support the extraction of the required information, and finally the extraction of the required information itself.
The general workflow for processing MLS data for road and railroad projects can be outlined as follows:
1. System calibration: fine-tuning of the calibration values provided by system manufacturers. This is usually done based on laser data that is collected at a specific calibration site. The process is done with TerraScan and TerraMatch and the workflow is described in the TerraMatch Users’ Guide.
2. Project setup: import and modify raw trajectory information, creation of a TerraScan project, import of raw laser data. This is done with tools of TerraScan.
3. Drive path matching: improving the internal and absolute accuracy of the project data. This involves TerraScan and (optionally) TerraPhoto, but mainly tools of TerraMatch are used and the workflow is described in the TerraMatch Users’ Guide.
4. Laser data classification: cutting off overlap between drive paths, apply classification routines and possibly other automatic/manual processing steps. This depends on the purpose for which the data shall be used.
5. Extraction of information: this may include the analysis of the current situation, for example, on a road surface or along a road/rail track; or the detection and/or vectorization of specific features, such as paint markings, road breaklines, rails, overhead wires, or potentially dangerous objects.
The tools described in this Chapter are related to the last point in the workflow outline above.
Road data processing
TerraScan provides three options for road breakline extraction. There is the Find Automatic Breaklines tool for the automatic extraction of the road crown. The Find Road Breaklines tool can be used to extract the crown of a road and road edges semi-automatically based on approximate 2D lines. Finally, there is a special processing workflow that speeds up the digitization of any lines along a corridor. This workflow can be applied to MLS and high-density ALS data, and involves the Write section points routine and the Import Road Breaklines tool.
Draw Slope Arrows tool and Color by Slope display option can be used for water flow analysis on the road surface, for checking the superelevation of road lanes, and for detecting damage on the road surface, such as ruts.
Write Alignment Elevations tool exports road surface elevation values along an alignment element into text files. This may be required for further road surface analysis in other software products, such as the computation of the International Roughness Index (IRI).
Further functionality is implemented in TerraScan as macro actions, such as Compute section parameters and Find paint lines.
Road/Railroad data processing
There are some tools in TerraScan that are useful for both application fields, roads and railroads.
Place Railroad String tool is a useful tool for many purposes. It allows faster digitization of linear elements than any other CAD digitization tool.
One of them is the Draw Sight Distances tool that is applicable to ALS and MLS data. Line-of-sight analysis based on laser point clouds has the unique advantage that all objects in the road environment including vegetation are considered. Another tool, Draw Sign Visibility, analyzes the visibility of signs or signals from certain viewer positions.
Find Poles is a tool for detecting and vectorizing poles along a railroad or road.
Label Alignment Curvature and Label Clearance are tools for analyzing the radius of curved roads/rails and clearance distances below bridges or other overhead structures.
Fit Geometry Components tool derives geometry components from a surveyed centerline of roads, railroads, and possibly other corridor projects. Geometry components are required for design tasks, especially for the data exchange between different software products.
Railroad data processing
TerraScan has a few tools which are dedicated to railroad processing. They include classification and vectorization tools suited for ALS and/or MLS data.
Fit Railroad String tool is intended to be used for ALS data of railroads. It fits an approximate rail track centerline to the classified laser points on the rails. The resulting 3D line element follows the rail track centerline more accurately.
There are two tools for the automatic detection and vectorization of rails and overhead wires from MLS data. Find Rails tool creates vector lines along rail tracks based on classified laser points, a rail track cross section profile, and an alignment element. Find Wires tool is used for the vectorization of all kinds of overhead wires along rail tracks, tram tracks, etc. It creates vector lines and classifies laser points on wires. The automatic wire detection is usually followed by manual improvements of the wire lines which can be done with the Check Wire Ends tool.
