How does it work? What makes it different?

The GS18 T allows to measure and stake out points faster and more conveniently than ever before. With the GS18 T, it is not necessary to level the pole vertically while doing a measurement or while setting out. You can literally forget the bubble (#ForgetTheBubble). Following a Q&A with Leica Geosystems GNSS Business Director Bernhard Richter about the new product, the following interview with Application Engineer at Leica Geosystems Paul Dainty gives us deeper insights about how to use the new Leica GS18 T and how it works.

What makes the GS18 T different? How does it work?

The Leica GS18 T is different from any other product in the market because it does not rely on a magnetometer to correct the pole tilt for each measurement. A magnetometer is affected by metallic objects, like vehicles, iron fences and beams or even reinforced concrete, all of which are often found on construction sites. In order to provide accurate and reliable tilt values, Leica Geosystems developed an application-specific, powerful and lightweight inertial micro unit (IMU), which is built into the GNSS antenna. The real -time tilt compensation combines GNSS data with the IMU’s tilt and direction values. Different to magnetometer-based GNSS antennas, the GS18 T’s tilt compensation does not need to be calibrated and is immune to metallic object interference.

What about the measurement performance in difficult conditions, such as urban canyons or woods with heavy canopy?

Like the Leica Viva GS16, the Leica GS18 T is a self-learning GNSS Smart Antenna with a high-class performance. This adaptive measurement engine with RTKplus provides measurement engineers on construction sites with the best position by automatically selecting the optimal signal combination. In addition, the GS18T is well prepared for the future. With its 555 channels, it is able to track all signals from all major GNSS systems worldwide, like Glonass, Galileo, BeiDou or QZSS (more details can be found in the GS18 T datasheet).

And how accurate are the measurements made with tilt compensation?

The accuracy depends on many factors. There is the accuracy of the GNSS position. If we look at the specified RTK solution, it is the same as with the GS16 – typically 8 mm + 1 ppm (single baseline length) Hz and 15 mm + 1 ppm (single baseline length) V. The accuracy of the tilt measurement is divided between the tilt accuracy and the direction of tilt accuracy. The tilt accuracy will typically be better than 0°12'00" and the direction of tilt accuracy typically better than 1°00'00". This means over a 1.8 metre pole length, the overall tilt accuracy is typically better than 20 mm at the pole tip with a tilt angle of 30°. This accuracy is comparable and most of the time better than using a conventional GNSS pole with a 20’ level bubble to make the pole vertical.

If the pole is tilted more than 30°, the accuracy of the tilted measurement reduces for two reasons:

1. Tilt accuracy declines as the tilt is increased and the direction of tilt accuracy has higher impact
2. With increasing the tilt angle, the antenna starts to lose track of some satellites, therefore reducing the GNSS position quality.

In any case, the position quality indicator in Leica Captivate shows the combined GNSS position quality and tilt quality, therefore representing the true pole tip accuracy.

Pole tip accuracy of 0.0175 metres, shown in Leica Captivate v3.0 on the field screen.

Does staking out also work with a tilted pole?

Yes, the tilt compensation can be used in any Captivate app where you can measure, meaning staking out is also much quicker and much more convenient than ever before. When setting out with conventional GNSS equipment, several different steps have to be done at the same time:

• Watching and interpreting the instructions on the screen
• Orienting, moving the pole according to the instructions
• Holding the pole vertical.

Holding the pole vertical, though, is no longer needed. With the GS18 T and the new Captivate v3.0, setting out is hugely simplified and a completely new experience. Utilising the tilted pole information and sensor heading, the intuitive 3D stake instructions now make it much easier to navigate to a stake point.

Staking out drastically simplified: With the powerful and intuitive 3D viewer, navigating to the point is easier.

What does Leica Geosystems mean with "Measure difficult to reach points that could not been measured before"?

With a conventional GNSS RTK rover, points like building corners, walls, fences, light posts or points underneath obstacles, like cars, cannot be directly measured with a vertical pole. To measure a building corner for example, you would have to measure a point nearby, and apply an offset to the point or measure it with an alternative method such as a total station – both options take time to do that reduces productivity. With the GS18 T, a building corner can be measured directly because the pole can be tilted and the pole tip placed easily and quickly to the corner. The same goes for all other difficult to reach objects, meaning the GS18 T makes measuring easier and quicker than ever before.

For a better understanding, I would recommend to watch the GS18 T how-to-video:

Isn’t the accuracy going to be affected, measuring next to buildings?

That is a very good question and one that people have been asking. When measuring next to buildings, the amount of multipath is likely to increase and a part of the view to the sky will be obstructed by the buildings, reducing the number of visible satellites. This makes for challenging GNSS conditions. The GS18 T with RTKplus technology is self-learning, meaning the sensor will automatically use the best signals and widely mitigate the multipath signals to compute its position. As long as the sensor can track enough satellites, an RTK position will be computed and the GNSS position quality will be displayed. So, whilst the accuracy is not likely to be quite as good as when measuring with an open view of the sky, the displayed GNSS position quality can be trusted so that you always know what accuracy your measured point will have.

Where can the new Leica GS18 T be tried out?

Easily, just contact your local Leica Geosystems distributor and ask for a hands-on demo.

Paul Dainty
Application Engineer at Leica Geosystems