Drone Surveys: HexCam even more accurate with P4RTK

You may not realise it but you’ve probably seen a surveyor at work. You might have paid for a building surveyor to inspect a house you’re hoping to buy whilst hoping they don’t find any dream shattering cracks in the walls.  Or you may have seen surveyors walking around fields, on building sites or next to the road holding a long pole with what looks like a frisbee on the top. Surveying has traditionally been a ground based activity with a lot of legwork, or has involved climbing up scaffolding or looking out of cherry pickers to inspect hard to reach areas such as rooftops.

Drones are already reducing the risks to surveyors and other trades working at height by essentially acting as remotely controlled flying tripods carrying high resolution cameras. High quality video and still images can be beamed back to a surveyor standing safely at ground level and can also be carefully reviewed offline to see if any repairs or a more targeted close-up inspection are needed.

Drone images, captured in the right way and with the right equipment, can now be used for something far smarter. Take enough overlapping images from the right height and the right angles, and powerful software can now be used to produce high quality 3D models called “point clouds” which in turn can be used to generate surveying drawings. How does this happen? Each photo taken by the drone has a ‘geolocation’ (GPS coordinates and height above the ground) hidden within the file and the software uses this information to help locate thousands of points within each image to build up the 3D picture.

The problem with ‘standard GPS’ used in things like smartphones, sat-navs and in most drones, is that it’s not particularly accurate. Fixed locations can appear to wander from one day to the next by up to ten meters and that’s no good for surveyors used to working to sub-centimeter accuracy. One solution is to set out lots of ‘Ground Control Points’ or ‘GCPs’ and locate these precisely using very accurate and expensive surveying equipment. These points then appear in the photos and the software, as it knows their exact surveyed position, will ‘tie’ everything to the GCPs dramatically improving the accuracy of the 3D model. But this still relies on someone doing lots of leg work setting out and measuring GCPs, and the drone’s position (and hence each photo’s geolocation) is still controlled using standard GPS.

So how is expensive surveying equipment able to fix a point on the ground so accurately? Surveyors use a positioning system known as ‘RTK’ or  ‘Real Time Kinetic’. It takes the standard ‘wandering’ GPS signals from multiple satellites, monitors them over time and, using some very clever algorithms, works out the real accurate position. Until now, putting such RTK positioning into drones has been extremely expensive but recent developments in drone technology mean that we can now access high accuracy RTK positioning at much more affordable prices and using much smaller drones.

HexCam can now survey large areas to the same accuracy as traditional ground-based RTK equipment with only a minimal need for Ground Control Points. Site survey times can be cut dramatically and there’s no longer a need to stick that pole in the ground every 10 meters. In fact the drone effectively gives a reading every few centimeters.

As an example, HexCam recently surveyed a 300 hectare site using RTK drone technology.  Traditional surveying methods would have taken approximately 20 days. With the RTK drone,  we captured the data within 2 days, confident in the knowledge that the results were accurate to the same standard.

Drone usage for surveying also removes the need to trudge or drive over rough, environmentally sensitive or perhaps even dangerous terrain, making affordable surveying possible in these tricky environments.  

If you’d like to know more about how RTK positioning helps us to provide accurate drone-based surveying then please contact info@hexcam.co.uk or call us on 01603 327676.


4 Considerations for flying drones in Winter

Flying drones throughout the winter is a necessity to maximise available time for ongoing surveys. Often, conditions in the winter can be perfect for surveying but there are some issues that you should be aware of when flying yourself or hiring in an operator. So here are our top 4 winter drone considerations.

1)      Batteries
The lithium polymer batteries in drones do not cope well with cold conditions. Under some circumstances you can lose 30-50% of your flight time. Generally, batteries need to be kept at least 20oC to function effectively. The cold can also have an impact on the battery life of ground equipment as well. Some types of drone will not allow you to take off if the battery temperatures are too low, but others will allow you to take off, but potentially the drone could fail if power demand increases.

2) Light
Aside from the obvious lack of daylight hours in the winter, the winter sun is much lower even at midday. As a result, working can be more difficult due to the fact that the sun can be low in your eyeline when flying. Often the ground lighting in winter can be an issue, with relatively bright skies and darker ground leading to issues with the camera coping with contrast. Particularly when surveying in the winter for mapping and modelling, harsh shadows can cause very dark areas and loss of detail in images.

3) Fingers
Generally, when we are outside in the winter we move around a lot and wear gloves to keep warm. When flying a drone we tend to stand very still and hands are relatively exposed. In terms of health and safety, it’s really important to be aware of how cold you are getting and to take breaks regularly to warm up and ensure your hands are working properly!

4) Condensation
When moving drones between warmer and colder environments it is really important to acclimatise the camera. Even at different heights the air temperature and humidity can be different. In an early creative wind turbine shoot, the drone got very cold on the ground and, when it got to about 30m up, the lens instantly fogged as the air higher up was a bit warmer. You may also get a lot of condensation on your kit when you get back indoors.