Technology Section Feature
Chief Operating Officer, Nextcore
When you go to buy UAV LiDAR, a common question you are likely to have is which GNSS Base Station should you buy to go with it? The short answer is: “like most things survey, it’s complicated.”
Let’s start out by saying we don’t sell GNSS base stations and we have no financial relationships with any suppliers, manufacturers or resellers of them. We do however need to ensure our customers get a base station that will work to Nextcore’s requirements so that we are not dealing with customer support issues that are not of our making.
What is a GNSS Base Station?
A base station is a tool that you place on a survey tripod usually over an already known point. In simple terms, it watches satellite frequencies for their position in the sky and aggregates them together in order to maintain a constant understanding of this point on earth as well all hurtle through the universe on a really big rock.
As you can imagine these stations are really important for surveying. They give the surveyor a set of observations that can be included in a survey to improve the accuracy of the survey’s known position at the time the survey was done.
Why do I need a GNSS Base Station? Doesn’t the drone have GPS?
Whilst the drone and most LiDAR systems have their own GNSS receiver, this receiver is hurtling through the sky, not sitting peacefully on a known point observing satellite signals. We need a base station once we land our payload to post-process this known position against the flight trajectory of the payload. You can get a point cloud out of the system without a base station but the global accuracy of the survey will be poor.
A point of note here is that you need to get the best quality system you can afford, some simpler systems simply do not observe enough frequencies or satellite systems to be able to provide the Nextcore systems with enough reference to generate a clean point cloud you need to collect frequencies at least every second.
Are there alternatives to buying a base station?
Yes, and in some parts of the world buying a base station is not even necessary. This is because in some parts of the world there are very good networks of static systems that release positional data via subscription services.
You should be able to determine the best service available in your area but if you are like us in Australia and these stations are few and far between, it is not worth the risk and you often need to collect your own data. Generally, you will need to find a station within 20km (12 miles) of your survey.
So what system should I buy?
The simple answer is that anything that provides you with L1 and L2 observations and can produce a RINEX file of at least 2.11 or higher.
You’ll need one that provides observations every second and can see these satellites: GPS, GLONASS, Galileo, Beidou. There is a huge variety of systems and we don’t really recommend a specific one other than to advise that there is a huge variation in the quality and price of systems. Top shelf systems used by most surveyors include: Trimble, Topcon, Sokkia, Leica etc. There’s also a growing number of lesser-known systems that are coming in with very aggressive pricing in the market. Lower cost systems tend to be tailored to specific applications and may not provide the accuracy or repeatability desired .
Because our system works with the DJI m300 we often get asked by customers if they should or could use the D-RTK2 system with it. We do not recommend doing this although it can be done. Because DJI creates proprietary equipment, generating reliable RINEX files for the DJI RTK system is a difficult workaround and this system is an example of a lower-end one in terms of satellite fixes and reliability. If it’s absolutely what you need to conduct jobs then we can make it work for you but we recommend a higher grade survey level system if you wish to produce high-grade survey level results.
If you are currently using a different system from what we have suggested here with our products and are getting great or terrible results, we’d be keen to learn about your experiences with them.
Let me know what your UAV LiDAR challenges are. Drop me a note at: nextcore.co/contact
About the author:
Speak to our expert support team…
We have an expert support team and global network of distributors who can demo our products and discuss your specific project requirements, so use the form below to get in touch or check our distributors list here.