Our GeoConnexion column: 4 things to consider before purchasing a survey-grade GNSS

In his last column, KOREC’s Mark Poveda delved into the crucial questions to consider before buying a 3D Laser Scanner. In this column, he turns his focus to four important factors to weigh up before making an investment in a GNSS survey-grade receiver.

In his last column, KOREC’s Mark Poveda delved into the crucial questions to consider before buying a 3D Laser Scanner. In this column, he turns his focus to four important factors to weigh up before making an investment in a GNSS survey-grade receiver.

Benchmark Surveys and the Trimble R12i

Across the geospatial industry, we’re seeing a bigger shift towards people using GNSS for their survey grade data collection and setting out operations, thanks in part to developments that have increased their ability to work accurately in challenging GNSS conditions such as urban canyons or under tree canopy. However, it’s important to state that if it’s high-accuracy, mm positions you’re after, then a total station will always be your go to.

In this column, I’m going to take a look at four GNSS areas it’s worth considering, especially if you’re keen to avoid time consuming total station set ups in your day-to-day survey work.

1. It’s not about the number of channels, it’s about how your receiver handles and decodes them

    When choosing the correct receiver for your purposes, it’s important to understand that most of them now support multi-constellations (GPS, GLONASS, Galileo, BeiDou), but it’s also important to check that they also support L1, L2 and L5 frequencies which mitigate signal interference in harsh GNSS environments. For example, Trimble’s ProPoint technology, found in several of their receivers, takes signals from all available constellations via three frequencies and uses dual core receivers for fast and accurate precision in challenging survey scenarios. My advice here would be to test repeatability of positions in these conditions during a field trial. We don’t want the spoofed accuracies that can occur with some receivers and this is the only way to ensure that doesn’t happen.

    2. RTK and Correction Services for positioning security – choose wisely, they’re not all the same

    Your RTK and Correction Services are key to continuous centimetre positions in the field and especially if you’re likely to be working where there’s patchy mobile coverage or your signal may drop in areas like quarries. If you want to avoid getting the total station out for those few points you need when there’s no signal, then it’s important to check that your receivers can also ‘bridge the gap’ using satellite corrections. KOREC customers report that the xFill function on their Trimble receivers, which does exactly this, saves them around 30 minutes of site time by avoiding a total station set up, it all adds up on downtime cost savings. Sometimes they’re not even aware the feature has kicked in because work is continuous and uninterrupted. Again, something to check on your field test.

    3. Environmental durability and endurance – will your expensive investment survive the conditions you work in?

    Construction sites are demanding places to work in and on top of that, did you know that last year rain fell on 171 days in the UK!

    If your expensive investment is going to handle the British weather as well as tough site conditions, then you’ll need an IP65 rating for your receiver, or if you want it to withstand submersion, then IP68, plus you’ll need MIL-STD810G or H for ruggedness for both your receiver and controller. Especially, take a really good look at the build quality during your field test and check out whether it comes with local servicing and repairs from your GNSS supplier. 

    4. It’s all about the workflow – protecting your data and turning it into manageable information

    Finally, a successful survey isn’t just about the receiver, it’s about collecting, processing and analysing that data and of course, protecting the information you’ve collected. Unfortunately instrument theft is a common occurrence so we definitely recommend that your receiver has the ability to sync with secure cloud storage and also that you can choose where it is hosted rather than it ending up in a random location anywhere in the world.

    It’s also important to consider the end-to-end workflow and ensure that yours is futureproof. For example, is your collected information compatible with your back-end packages if you’re an n4ce or SCC user? Seamless integration is vital for saving office time on the processing and decoding of your collected data.

    Whilst I hope this information is a good guide to what to look for in a GNSS Receiver, my best advice would be to rigorously check before you buy with an extensive field test and especially, check its accuracy and repeatability in different conditions.