In 2016 a few new models are introduced but overall it’s a year of consolidation but watch out for the opportunities of precise point positioning. Read this Engineering Showcase article to find our more about the latest GNSS Receivers and technological developments in 2016.
Engineering Showcase editor Richard Groome suggests that manufacturers have been consolidating their ranges of GNSS receivers. Read more on the latests GNSS Receivers from Leica Geosystems and Trimble here:
GNSS Receivers, such as Leica’s GS08, GS12, GS14 have gone. The GR10 and GR25 reference stations have been replaced by the GR30, which can handle BeiDou data and the GMX910 has been introduced, for monitoring applications.
Trimble has a new GNSSreceiver, the R2 whilst the R8s and R9s, are now marketed as suitable for precise point positioning (PPP), joining the top of the range R10, which was launched with that feature. It is clear that the manufacturers have seen Galileo and Beidou just round the corner and have responded.
GNSS Correction Services
A subtle, or maybe not so subtle, adjustment is the treatment of PPP. Trimble offers a full PPP service called CenterPoint RTX. With a CenterPoint RTX subscription, the receiver can receive GNSS corrections via satellite or the internet and is able to compute positions to a precision of 4cm in horizontal and 9 cm in vertical from 30 minutes of data. In other words it could be particularly useful in places where there is no network RTK service.
However, if using satellite correction delivery, the receiver still has to be able to track the satellite delivering the RTX corrections. Other than polar regions and a chunk of central Asia, most of the planet is covered, but obstruction by trees and topography still has to be considered.
Trimble also offers a service called Trimble xFill on its R10 receiver. This service can come into operation when the receiver loses contact with the network RTK service, or its base station – when the phone or radio goes down. For five minutes, it will continue to generate positions by using corrections from CenterPoint RTX. After five minutes the service stops, unless the user has subscribed to CenterPoint RTX. Leica offer a similar gapfilling service called L-band SmartLink, but the corrections are available for twice the time after loss of communications with the base.
One would expect positions to degrade during periods when the receiver is depending on corrections from xFill, and Trimble’s FAQs state that the degradation is 10mm per minute (RMS) in plan and 20mm per minute (RMS) in height. For those who have paid the subscription, the precision levels out after five minutes and “will not exceed 6cm horizontal and 14cm vertical” while using Trimble xFill with CenterPoint RTX – assuming good GNSS visibility.
Chasing the centimetre
For those of us who have to chase the centimetre in the vertical the prospect of 14cm will cause a shudder. Indeed, in the wrong hands it is arguable that xFill is a licence to produce poor quality data, especially when the marketing blurb encourages complacency by stating that “xFill maintains RTK level accuracy” during an outage. Thankfully, it can be switched off, but will probably only be switched off by those who have read and understood the small print.
Leica literature is not quite so bold in its claims. It states that horizontal accuracy is approximately 5cm after ten minutes, preferring to illustrate accuracy in the vertical only as a line on a graph.
The prospect for the future should be improvement in the results obtained using PPP, thanks to more constellations and satellites as well as faster and more accurate computation of satellite orbits. More satellites should also result in better position-fixing overall and particularly in less than optimal environments.
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