3D laser scanning workflow overview for newbies

June 18th, 2019, Published in Articles: PositionIT

This article looks at  point cloud basics and a workflow which will enable capturing and processing of a 3D laser scan.

Laser scanners collect surface data about an object or structure by beaming a laser repeatedly off its surface and plotting points (equivalent to each beam that is emitted) into what is known as a point cloud. After the field work of 3D laser scanning is complete, the scan data is brought back into the office for processing.

Reality capture is a broad term  which includes all means of capturing an existing environment, be it with laser scanners, cameras, unmanned aerial vehicles (UAVs) or other methods. Reality capture is divided into three phases: the survey phase, the treatment (processing) phase and the final modelling (analyses) phase.

The reality capture workflow would start with data from the 3D surveys to create a point cloud. Point clouds from different survey setups are processed on high-performance workstations and connected to one another (registered) in software such as Autodesk ReCap. Then to colourise the point cloud, technicians superimpose photos over joint point clouds. From this technicians can model the data in 3D for end users.

How to unlock value

Mapping and scanning systems are good solution when a large amount of asset data needs to be collected in a short time. Software can be used to make measurements and extract the necessary information from the scans to make volumes and other calculations visible to everyone. It also eliminates the need to revisiting a site to gather missing data. Furthermore, laser scanning can help keep field personnel out of harm’s way, as it allows one person to collect site data  for volumes, site maps and overviews, which previously required larger teams.

Workflow overview

The workflow involves five steps

  • Identify the scanning scope area
  • Capture a series of scans
  • Merge the scans
  • Align the scans with control coordinates
  • Produce a 3D CAD model or other desired deliverable.

The below workflow example uses a Topcon GLS-2000 laser scanner and Autodesk ReCap software. The 3D laser scanner uses a pulse of infrared light to measure objects in their real-world position. The scanner collects data on every reflective surface in range and in line of sight of the laser. A typical scan setup can produce anywhere from 40 to 150-million individual 3D data points, each containing accurate x, y, and z information.

Fig. 1: A 3D laser scanner.jpg

The GLS-2000 offers one-touch operation for non-specialist, and satisfies the survey professional with occupation and backsight operation. It provides a 360°(H) and 270°(H) field of view, enabling the capture of point cloud data in closed-in areas such as building interiors, mechanical rooms, under bridge spans, pipe racks and other challenging spaces. Distance measuring range is user-selectable to accommodate scanning applications that require short and long distances up to a maximum of 350 m. Depending in the job site requirement, the measurement mode (with different laser output), can be switched between Class 3R and Class 1M, to accommodate eye- safety concerns in populated areas.

The ReCap software processes point cloud datasets and provides the ability to aggregate, enhance, clean, and organise the data, and to prepare it for use in other Autodesk products. The scan data is imported, indexed, and saved as a project. The software converts the scan files to a proprietary format which can be read by other Autodesk programs.

At the start of this process, the user can adjust the number of points imported by changing settings for noise, distance from the camera, intensity range, and decimation values. The indexed scan files are then saved in a Reality Capture Project (RCP) file format that references, but does not contain, the files. The software supports the import of structured scans (including RealViews and registration where applicable) for individual or multi-scan E57 files. The scene and its objects are measured, filtered, cleaned, and organised.

Fig. 2: A 3D point cloud.

A number of methods are available to organise the indexed data to remove or hide portions of the point cloud. Scan Regions can be turned on and off, temporary clip regions specified, scan files turn off or removed, and unwanted points permanently deleted. By viewing the scene using different colour modes and lighting, users can gain insight into elevations and reflectivity. Indexed scan files and projects can be opened or attached in other Autodesk software programs to provide realistic context for 3D models.

Working with point cloud data

Visualisation tools in ReCap such as colorisation, light addition or selection of Limits Boxes are available. This helps the user choose the region in which they want to use this data. From this selection users can make measurements, notes, regions creations, export the selected sector and  animated video realisation. The ReCap 360 platform also allows user to share this data in a web interface for collaboration with all the project’s stakeholders. Users can then take action or directly annotate photos to share information.

The optimised integration between hardware, software and process automation cuts down time from reality capture and final deliverables. Some advantages include better planning and costing, such as getting fast, actionable data on stockpile volumes on a mine.

References

[1] Louque, L. (2016). Autodesk University. Retrieved from Laser-Scanning Workflow Process for Chemical Plant Using ReCap and AutoCAD Plant 3D: https://www.autodesk.com/autodesk-university/class/Laser-Scanning-Workflow-Process-Chemical-Plant-Using-ReCap-and-AutoCAD-Plant-3D-2016#downloads
[2] Roland, T., & Fauconnet, F. (2018). Autodesk University. Retrieved from Autodesk: https://www.autodesk.com/autodesk-university/class/Laser-Scanning-Workflow-ReCap-Power-Station-Renovation-Project-2018#downloads
[3] Topcon. (2019). Mining Solutions. Retrieved from Topcon: https://www.topconpositioning.com/mining#panel-solution-3801

Contact Carel Rootman, Worldsview Technologies, carelr@worldsview.co.za

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