Our Frequently Asked Questions about Ground Control provide insight into why it’s important and how to establish it. If you have a question we’ve not covered please do get in touch.
- Why is it important to establish ground control in a UAV LiDAR survey?
- Why do I need Ground Control Targets to establish ground control in a UAV LiDAR survey?
- How do I use LiDAR Ground Control Targets?
- Why should I purchase Routescene’s Ground Control Targets?
- How many Ground Control Targets do I need for my survey?
- How do I identify the Ground Control Targets in my dataset?
- How do I verify the accuracy of my survey?
- Can I identify Routescene’s Ground Control Targets in photogrammetry too?
- Are Ground Control Targets included in a Routescene UAV LiDAR System package?
- What’s included with a set of Routescene’s Ground Control Targets?
- Ground control case studies
- What do all these geospatial and LiDAR terms mean?
1. Why is it important to establish ground control in a UAV LiDAR survey?
Establishing ground control will provide an independent check of your results; it will also enable you to demonstrate the level of accuracy that has been achieved. Plus, it avoids data processing issues and assists with the calibration of the sensors on the drone: all of which improve the confidence in the accuracy of the survey.
You can use Routescene’s Ground Control Targets to easily and quickly establish ground control.
2. Why do I need Ground Control Targets to establish ground control in a UAV LiDAR survey?
In a LiDAR point cloud the points are discrete with space around each individual point. This makes if very difficult to identify a feature if the feature is between two points. To remove this problem, and to enable calibration and accuracy analysis to be performed, it is typical to use a flat surface and analyze each axis individually, which is mathematically far more robust.
In practice finding a flat surface in a highly vegetated undulating terrain is highly improbable! Routescene developed special LiDAR Ground Control Targets for this purpose.
3. How do I use LiDAR Ground Control Targets?
Routescene’s specialist LiDAR Ground Control Targets are large discs to be positioned within your survey area. Placed on known geographical points called Ground Control Points (GCPs), the coordinate of each Ground Control Target is established using an accurate and independent survey technique.
The targets are highly reflective and can easily be identified in the resultant point cloud.
4. Why should I purchase Routescene’s Ground Control Targets?
We are the only manufacturer offering Ground Control Targets specifically designed for drone LiDAR mapping. Our Ground Control Targets can be used with any drone LiDAR system.
We have evolved the design of our Ground Control Targets over the years, experimenting with a variety of different designs, materials and methodologies. Through continuous improvement, based on our own field experience and customer feedback, our LiDAR Ground Control Target design is in its fourth iteration.
5. How many Ground Control Targets do I need for my survey?
The number of Ground Control Targets you will need depends on the size of your survey area: we advise 4-8 targets are used for a 500 x 500m area to enable boresight calibration and to provide check points.
6. How do I identify the Ground Control Targets in my dataset?
Routescene’s Ground Control Targets are covered in a highly retro-reflective material and are mounted on a small tripod to raise them from the ground. This ensures that any vegetation or high grass is not accidentally classified as being part of the Ground Control Target in the point cloud. 60cm in diameter, typically each Ground Control Target will be hit 200-300 times by the lasers from the LiDAR system.
The retro-reflective material provides a high-intensity return and the Ground Control Target is easily identifiable in the resulting geo-referenced point cloud. You can directly compare the known coordinate of the physical Ground Control Target with that visible in the point cloud.
7. How do I verify the accuracy of my survey?
One of the challenges when managing large sets of LiDAR data is ensuring the integrity of the data.
In LidarViewer Pro, Routescene’s LiDAR post processing software, you can produce a Quality Assurance Report to ASPRS standards for every survey you perform to verify your results. The results also enable you to identify errors as soon as possible and decide on a remedy, while demonstrating to your client that the required level of accuracy has been achieved.
8. Can I identify Routescene’s Ground Control Targets in photogrammetry too?
Yes. Routescene’s Ground Control Targets include a checkered photogrammetry decal for easy identification in photographs.
9. Are Ground Control Targets included in a Routescene UAV LiDAR System package?
Ground Control Targets are an upgrade option and can be included when we prepare a UAV LiDAR System quote for you.
10. What’s included with a set of Routescene’s Ground Control Targets?
The Routescene Ground Control Target set includes:
- 4 x Ground Control Targets
- 4 x Mini Tripods
- 1 x Tough carry bag with handle for 4 x GCP Targets
- Procedures on how to deploy, survey in Control Points and use the results in QA Reports.
11. Ground control case studies
These use cases demonstrate the benefits of using Ground Control Targets to establish ground control:
LiDAR archaeology discovered 750 year old structures, USA
Ground control targets used to calibrate the system for boresight misalignment. Best practice enabled a return site visit to resolve a discrepancy.
UAV LiDAR used to monitor landslides safely, UK
Establishing ground control enabled consistent comparisons to be made over time to identify the location and scale of ground movements.
LiDAR mobile mapping system used to plan upgrade of powerlines, Canada
Ground control was established to calibrate for drift, which is typical in a longer vehicle survey.
12. What do all these geospatial and LiDAR terms mean?
To help you understand geospatial, UAV LiDAR and data processing language here’s a glossary of commonly used terms.