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Geomatics

 
 

WSP delivers surveying and mapping solutions for the entire project lifecycle with speed and certainty. Our crews are first on the ground supporting some of the largest projects in Canada. Regardless of the project size or location, we are there, from field to finish.

 
 

The Use of UAVs vs Traditional RTK Survey: A Project Case Study

May 04, 2017
 

 

Project Background

WSP was contracted to evaluate the accuracy of using UAV (unmanned aerial vehicle) photogrammetry (using photography in surveying and mapping) technology to provide stockpile volume calculations.

For this project, we utilized the Sensefly RTK eBee for our UAV platform, which used a Canon G9X 1” sensor camera with RTK (real time kinematic) enabled. We utilized the Trimble R6 GNSS RTK to establish ground control and to acquire RTK GNSS volumes. In addition, the piles in question were also scanned by laser scanner to give a benchmark to the quantities. Due to the high amount of vegetation in pile 3, and the moderate vegetation in pile 1, additional cleanup of the point cloud (set of data points) was required.

Observations

While UAV based surveying does offer some exciting potential, not all situations are conducive to the use of UAV based photogrammetry surveying. Overall, we observed that the data resulting from the UAV survey compared to the RTK survey was considerably more accurate and required significantly less time to acquire.

Ideal Conditions

Photogrammetry relies on the use of RGB-based cameras and overlapping imagery to establish elevation data. Because the cameras are RGB-based, the information captured is purely based on what the RGB imagery can acquire. If heavy vegetation exists, the photogrammetry process will also include the vegetation in the final model.

Benefits Using UAV Survey Methods over Traditional Methods

The use of UAV technology in the geo-spatial industry has no doubt changed the methods at which the data can be gathered. It, like many other geo-spatial tools, is not a magic bullet and is not necessarily the default best solution. WSP has a wide array of tools and resources we can access and would evaluate the project prior to selecting the method of data gathering. 

Below is a list of some benefits of using UAV technology.

  • Risk reduction. Every year work accidents take place in the Canada, half of which are related to heights and the risk of falling. Medical costs and costs for absence from work amount to hundreds of millions per year. The use of drones for specific monitoring, inspection and survey tasks now performed by people can significantly reduce these risks.
  • No need to shut down installations. During inspections, installations often need to be shut down temporarily, involving high costs due to loss of productivity. Using drones capable of inspecting functioning installations in a short time span makes the shut-down superfluous.
  • Improved overview. Flying at low heights, drones are capable of creating a very sharp image and a clear overview which can be used to actively monitor and inspect activities, installations, infrastructure and buildings on the surface. In addition to using UAV technology to actually perform the survey, inspection or other function, the UAV can be used to scout the site in a cost effective manner.
  • Survey of inaccessible locations. A drone can fly where people or vehicles cannot access, for example over swamps, densely forested areas and locations of suspected UXO (Unexploded ordnance). Drones make these areas accessible for airborne surveys.
  • Improved data density. Compared to manned helicopters and planes drones can get much closer to the survey goal, resulting in improved data density and quality of the survey. Typically the resolution and GSD (ground sample distance) is greatly improved using UAV technology.
  • Faster data acquisition. Drones can perform surveys or inspections on the surface or in the air in a much shorter time span. Because less people and equipment are involved, in most cases the necessary security measures and time required on site can be reduced significantly.
  • Higher data resolution. Compared to manned helicopters and planes, drones can fly much closer to the surface, improving the data resolution and therefore the quality of the survey.  
  • Lower costs. Drone research is often cheaper because installations don't need to be shut down, inaccessible areas become accessible, data acquisition is faster and the necessary workforce and equipment required in the field are reduced.

Considerations when using UAV-based Photogrammetry

While UAV base photogrammetry techniques are excellent at capturing hard surfaces, they show their weakness when trying to capture true ground when the ground is obstructed by tall grass, weeds, trees and bushes.  While software solutions have come a long way in estimating true ground, it is still not the single best tool or technique to use in this circumstance and would best be served by a combination of techniques. On typical, clean stockpile sites with very little vegetation, UAV-based photogrammetry is an excellent method. Used in conjunction with RTK, GPS control points and reliable repeatable measuring environment can be established.

Please contact us about your upcoming projects and we would be happy to discuss the methods that would be best fit for your project.

 

Contact:

Colin Hubick
Colin Hubick UAV Manager