Airborne mapping and laser scanning

A high-precision railway mapping project combined airborne mapping with mobile laser scanning for a ‘proof of concept’ for a transport corridor study.

Investment in airborne mapping earlier this year will allow Maptek™ to offer a comprehensive digital survey capability. DroneMetrex photogrammetric mapping and I-Site™ laser scanning both capture high quality, accurate data for users to easily measure and monitor surface changes.

A ‘proof of concept’ for a road-railway crossing study proved that the survey methods are complementary.

Airborne mapping

Aerial mapping with unmanned aerial vehicles (UAVs) is safe, efficient and cost effective. The DroneMetrex TopoDrone-100 reliably mapped 0.5 km on each of the 4 sides of the approach to a road and railway intersection. Capturing highly accurate data took only 2 hours.

The aim of the project was to create a 3D real world scene for obscurity analysis. It was essential to record the scene to show the perspective of both train and vehicle drivers when approaching the crossing. Airborne mapping data also provides valuable input for future repair and upgrade work.

The traditional lidar approach for corridor mapping was not economically viable for the small project area. Conventional ground survey would require temporary closure of the railway to ensure safety. Operating the UAV from the nearby field avoided interference with road traffic and rail movement.

The UAV captured aerial imagery with 25 mm repeatability in height. The DroneMetrex photogrammetric mapping system achieves high accuracy by addressing geometric errors at the point of data capture.

Deliverables included a very dense 3D point cloud, digital orthophoto mosaics, DTMs and 3D line mapping.

‘A unique synergy of the most advanced terrestrial and UAV mapping systems made it possible to generate a detailed and accurate database for visualising and measuring the scene in true 3D,’ said Tom Tadrowski, Managing Director of DroneMetrex.

Laser scanning

Adding terrestrial laser scanning to the project allowed capture of data which may have been obscured by vegetation, adding to the accuracy of the 3D scene.

The Maptek I-Site 8810 was mounted on a vehicle and driven along the road. Stop-Go scanning is extremely efficient. In just 2 hours, 21 scans were captured.

Combining point cloud data from aerial and terrestrial systems provides a more immersive data experience. Authorities can take measurements to validate that infrastructure is built and maintained to safety standards.

The benefit of the laser scan data lies in being able to show what happens when the scene changes. For example it highlights how removing a tree could improve driver visibility and impact on the safety of the crossing.

The trial demonstrates the way that photogrammetric mapping and
laser scanning together can deliver a better result.

Accurate digital models and photographs also provide the basis for analysis and decision making in mining, geospatial, agriculture and infrastructure applications.

Maptek is working on a total solution to simplify workflows, automate and semi-automate repetitive procedures, and decrease processing time.

How airborne mapping works

Is airborne mapping the same as photogrammetry?

Photogrammetry is the science of making measurements from photographs. The UAV is one vehicle for airborne mapping. The DroneMetrex system uses photogrammetry to calculate a dense point cloud and then a 3D surface. Mosaic and/or orthorectified aerial photos are also produced.

Does the UAV take photos, or does it have a scanner attached?

The UAV captures photos and orientation information in flight. All of the data is used in the calculations, resulting in multiple deliverables such as data, imagery and models. Data from ground-based laser scanning completes the scene in areas with vegetation canopy, overhanging or complex structures.

Does the UAV fly constantly over an area, continually taking aerial photos?

Current systems fly 30-60 minute sessions, capturing aerial photographs. Flight data is downloaded and pre-processed in real time. Post-processing occurs after the UAV has landed. Most software packages take many hours to fully process the data, depending on the area flown.

How accurate is the 3D data?

The TopoDrone-100 UAV uses a gimbal to counter aggressive flight movements, ensuring the camera is always vertical. Data repeatability can be refined to 25 mm, given suitable operation. Combining geo-referencing with ground control points allows the processed data to be tied to the local coordinate system for higher accuracy.

Does the system require targets or ground control points?

The DroneMetrex system can use direct geo-referencing which involves logging accurate GPS data and post-processing with data from the local site base station. Ground control is not necessary with this method.

How safe is the system?

Airborne mapping systems enhance the safety of mine and industrial personnel. There is no need to approach active machinery or access unsafe terrain. Legal, operational airspace and training requirements, combined with site safety procedures, ensure the launch and operation of UAVs is as safe as possible.

How does the UAV take off and land?

The TopoDrone-100 is controlled by a ground operator. It is launched automatically by a catapult and remotely guided to slowly descend and slide along the ground to a stop in a designated area.

Where is the Maptek system in use?

Maptek only recently began investing in airborne mapping solutions. Many of Maptek’s customers are among the miners getting involved in UAV technology.

Does the system work with other Maptek products?

Integration with I-Site Studio, Vulcan and Eureka software extracts maximum value from airborne mapping data. I-Site 3D laser scanning systems naturally complement DroneMetrex aerial data.