There are alot of buzz words in the Drone industry about accuracy, like Centre-metre accurate or precision agriculture. But with drones there are only two types of precision; “Relative” and “Absolute”. Although both have their place in the Industry Relative is most common.
What is Relative Accuracy?, well lets say if you tape measure between two objects on a site and they are exactly 10 metres apart. Then you Drone map the site, find the same two objects in the processed map and measure with mapping software exactly 10 metres. This means the Relative Accuracy is high because the terrestrial measurement (Tape measure) matches the digital measurement in the mapping software.
This is the basic concept of Relative Accuracy! It can be centimetre accurate within the map but not on a global coordinate scale. Relative Accuracy can be achieved with standard drone gear and is accurate enough to perform basic Area and Volume Calculations using mapping software. Its also accurate enough for Crop and weed Scouting. This is currently what style of mapping we do at Oakdale UAV Solutions.
So what is Absolute accuracy? It includes Relative Accuracy and is also precisely incorporated into a universal Coordinate system, so no matter where you are on the map it is normally within a metre (sometimes centimetre) in relation to what ever Coordinate system is being used.
Absolute accuracy requires more expensive drone equipment including Dual RTK antennas and a camera that is synchronised with GPS timestamping. Also it may require a base station and Ground control points (GCP’s) which are special targets for accuracy validation. Absolute accuracy is normally required for surveying and civil engineering projects for precise setouts following a design.
With our XAG drone system we can utilise both accuracies. How? Well In Australia the surveying industry has a free system that operators can use known as the “Continuous Operating Reference Station” or “CORS”, which involves literally 100’s of permanently installed GPS survey stations on roof tops through out the country. These stations are constantly recording satellite positioning data for correction and triangulation.
When flight planning or flying our Spray drone we set up an RTK base station and we can link up to the CORS system via phone signal. This triangulates the base station’s position and height down to an Absolute accuracy less than +/- 1 metre. During flight planning we walk around with a rover unit to record points around the target area to create flight patterns. The rover talks to the base station via radiowaves and corrects the recorded points down to the centre-metre.
Now that all sounds great but sometimes you can’t connect to CORS! well that’s ok because the base station will resolve its position down to about +/- 10 metres Absolute accuracy. After the base station resolves, all points recorded with the Rover will have centre-metre Relative Accuracy between one another and the base station.
When returning to the same site and flying the designed flight paths it is also important to remember each point is relative to one another including the base station! if we place the base station 10 metres in the wrong spot, the whole flight area will be 10 metres in the same direction. This is a scary thing if you have alot of tall obstacles like trees nearby!😬.
Thanks for reading this post and If you enjoyed it there are more to come. Also if you are interested in my Drone services you can contact me through the contact page or Request a Quote.
