In the disciplines of Geomatics and Civil Engineering, accuracy and efficiency are paramount. Traditionally Surveyors have used total stations and GNSS equipment to perform topographic surveys of city streets. However, with advances in technology, modern tools like mobile SLAM (Simultaneous Localization and Mapping) LiDAR scanners have begun to replace or complement these methods, offering faster, more accurate and detailed data collection.

This case study explores how a NavVis VLX2 mobile SLAM laser scanner was used to create a precise digital twin of the site and a topographic survey plan to aid civil engineers in a traffic calming design of a busy city street.  

The Challenge: Designing a Safer High Vehicle and Pedestrian Area

Construction of a traffic calming design is intended to improve safety for motorists and pedestrians, encourage sustainable modes of travel, and to create a comforting environment for the community. Traffic calming designs typically involve constructing a variety of vehicle speed calming features such as speed humps, road narrowing and round abouts along with aesthetic landscaping improvements. To ensure that the design fit seamlessly into the existing environment, the engineers required a highly detailed topographic survey plan of the road’s terrain, existing features, and surrounding infrastructure.

The challenge for the Spitfire surveying team was to gather this data accurately and efficiently, while minimizing disruption to the road, as it remained open to the public during the survey process. Traditional surveying methods would have been time-consuming and potentially disruptive, leading the team to consider a more modern approach.

The Solution: VLX 2 Mobile SLAM Laser Scanner

The surveying team decided to use the body mounted NavVis VLX2 SLAM LiDAR scanner to complete the topographic survey instead of a drone mounted LiDAR sensor.  The busy road was located in between tall high rise apartment buildings and a mall parkade.  The parkade had an overpass access crossing the road and a tower crane was overhanging the street periodically.  A drone mounted lidar sensor would not capture enough detail because of the poor angles from a drone flight path above the nearby towers and because of obstructions blocking the view of the street.  This presented an excellent opportunity to try a mobile SLAM LiDAR scanner to capture a digital twin of the site. LiDAR (Light Detection and Ranging) uses laser beams to scan an area and capture the exact 3D geometry of the surrounding environment. Unlike traditional survey methods that rely on point-by-point measurements, a laser scanner can capture millions of data points in a fraction of the time, creating a dense and highly detailed 3D point cloud of the area. SLAM LiDAR scanners calculate their position continuously and generate a point cloud in real-time.  They are designed for use in motion and excel in GPS denied environments.  The NavVis LiDAR SLAM scanner was an ideal candidate to capture precise and comprehensive data in a GPS denied environment in a fraction of the time compared to traditional methods.

Planning the Survey

Before beginning the scanning process, the Spitfire team conducted a site visit to assess the best locations for setting accuracy control nails. The two-lane paved road, which was approximately 350 meters included sidewalks, utilities, signposts, light poles, planters, line painting, building facades and many other features which needed to be measured. The team strategically placed control nails throughout the site for the Mobile SLAM laser scanner to use as georeferencing, quality assessment and to correct drift in the trajectories of the mobile slam scanner. These survey control nails were then measured using a total station and aligned to government geodetic control monumentation.  

Data Collection

After completion of the control survey, the scan with the mobile SLAM LiDAR was initiated. The Spitfire Team utilized the NavVis VLX2 SLAM scanner from Cansel survey equipment to acquire the lidar and imagery necessary for the project. The data was acquired in a systematic manor starting at one end of the road, walking to the other end of the road and then back. The operator performed iterative loops throughout the site to collect redundant survey data that would aid the SLAM real-time alignment algorithm. When the scanner reached one of the previously surveyed control markers, the scanners reference mark was placed on the nail in order to georeferenced the scanner deliverables.  

In addition to the terrestrial data, Spitfire Drone Survey also conducted a drone photogrammetry flight to collect aerial orthomosaic imagery of the site. The same control points used in the terrestrial scan were used as control markers for the drone orthomosaic flight to ensure seamless integration of the two data sources.  

Data Processing

After the data was collected, the next step was to process the point cloud data. Specialized software was used to align and merge the scans from the different scanner positions, creating a cohesive 3D model of the site. This software also helped remove any extraneous data, such as points from moving objects (people, cars, etc.), ensuring that the final dataset was clean and reliable. Imagery from the drone was imported into a photogrammetry processing software to align and create an orthomosaic of the survey site that was aligned with the collected pointcloud.  

The pointcloud and orthomosaic was then used to extract key survey elements including curbs and gutter lines, sidewalk letdowns, driveways, retaining walls, bollards, street signs, paint markings, vegetation, building outlines, manholes, catch basins, water and gas valves and much more.  

The Results: A Comprehensive and Accurate Survey Plan

By using a mobile SLAM LiDAR scanner, the survey team was able to complete the project with several key advantages over traditional methods:

Speed and Efficiency

What would have taken multiple days with traditional methods was completed in just a few hours. The ability to quickly gather large amounts of data from multiple angles saved significant time, reducing project timelines.

Reduced Disruption

As the road remained open to the public during the survey, minimizing disruption was a key concern. The terrestrial laser scanner was non-invasive, allowing the survey team to gather data without blocking the road or disturbing pedestrians. The scanners could be used discreetly in areas that caused minimal interference with daily activities.

Rich Data for Design

The resulting point cloud data and topographic survey plan provided the design team with a wealth of information. They could clearly see the contours of the land, existing features, and even the canopy height of trees—all of which would aid the placement of new structures, road calming features, and landscaping elements. Supplemental to the pointcloud and aerial imagery, the NavVis also collected terrestrial imagery. Having the terrestrial imagery allows a designer to virtually walk down the survey site and see all aspects of the road in high definition. This feature could expedite the creation of the engineer’s design by viewing up to date street view imagery from the comfort of their office, saving time and money.

Conclusion

The use of a mobile SLAM laser scanner for creating a topographic survey plan significantly enhanced the efficiency and accuracy of the project. By capturing millions of data points in a fraction of the time required by traditional methods, the survey team was able to deliver a detailed and precise plan that served as the backbone for the successful redesign of the road.

This case study demonstrates the value of integrating cutting-edge technology like mobile SLAM laser scanning into modern surveying practices. It not only saves time and costs but also provides the high-quality data necessary for informed decision-making in complex design projects.

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