Augview is a GIS application that relies on accurate satellite positioning data for the application to be used effectively. Here, we look at the work Augview has undertaken to ensure the positioning data users receive when using the application is as accurate as possible.

Augview users work in the fields of utility asset location and management, and as such have a solid understanding of GIS and GNSS. They’ll also understand that with a system built around GNSS, accuracy testing (both in the R&D phase and ongoing) is a critical part of developing and managing the application.

At this point in time, GNSS receivers are incapable of providing 1 cm positional accuracy due to what is commonly known as GPS drift. GNSS positioning relies on very accurate measurement of the time it takes for a signal to travel from the satellite to the receiver.  However, the earth’s atmosphere and magnetic field perturb the speed at which the signal travels by a small and variable amount. As a result, the distance between the receiver and each satellite cannot be accurately determined.

Augview CEO Mike Bundock believes that in three to five years GPS drift issues will be largely overcome, as the technology evolves to automatically correct for the signal perturbations.

But for now, in order to mitigate any data errors associated with this drift, corrections generally need to be applied to the calculated position, using either satellite-based augmentation systems (SBAS) or ground-based augmentation systems (GBAS).

As part of the development of Augview, the team recently undertook testing across a wide range of devices to assess their ability to calculate an accurate and reproducible position both with and without applying corrections.

From the testing, three important discoveries were made.

When it comes to using a lone device without any real time correction, newer devices are generally (but not always) best. Newer devices will generally record a more accurate and reproducible position – without the need to apply corrections. However, accuracy is still limited.

With older devices, it is possible to integrate an external GNSS receiver via blue tooth or USB cable to provide real time corrections. Augview can assist clients with older hardware by recommending suitable external units to provide the most accurate satellite positioning data possible.

There are multiple approaches to performing real time corrections, including:

  • PPP (precision point positioning)
  • Differential corrections (DGPS)
  • Kinematic corrections (RTK).

If no corrections are being performed, even professional survey equipment will suffer from GPS drift in a similar manner to consumer grade devices such as tablets and smartphones. It’s important to note that survey grade equipment tends to have the advantage of a larger external antenna and more sophisticated signal processing which makes it achieve better positioning than consumer grade devices with internal micro antennas, especially in city areas with surrounding high-rise buildings.

It’s also worth noting that the size, quality and placement of the antenna plays an important role in acquiring better positioning – for example by filtering out multipath, which is the reflection of satellite signals from objects like trees, buildings and cars.

The team at Augview are continually testing mobile devices and external GPS receivers to measure the accuracy and reproducibility of the calculated position. Mike and the Augview team believe they are on the edge of a breakthrough in the area of low cost, high accuracy GNSS positioning – to ensure you don’t miss out on the latest Augview developments, sign up for the Augview newsletter.

Michelle Goldsmith

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