Trimble R12i  is an advanced GNSS system that provides high precision, reliability and productivity, even in complex GNSS observation environments. Trimble ProPoint, a real-time processing engine that calculates the best possible position using all available GNSS constellations and signals, runs on a dual processor with 672 channels which has been specially designed for this engine, with the main benefit being the determination of precise positions.

Thus, once Trimble R12i determines a position, it is automatically combined with IMU observations, which completes the mathematical positioning model by including the tilt and orientation of the pole. This is known as TIP: Trimble Inertial Platform.

The big news is that TIP improves its accuracy specification starting from firmware 6.43, reaching 3 mm + 0.15 mm/° horizontal accuracy.

 

The position will be precisely determined wherever the pole tip is located


The power of the pole tip

Trimble Inertial Platform is the technology that allows determining positions with a tilted pole. It is only necessary to reach the point with the pole tip to determine its coordinates precisely and quickly. This technology can be used either to determine positions associated with a topographic survey or for staking out. In both operations, the use of this technique is highly productive since it is not necessary to level the pole to obtain a representative position in terms of the point indicated by the pole tip.


Trimble ProPoint in challenging GNSS observation environments
(Courtesy of Rumbos Geomensura)


While GNSS precisely determines the position, it is necessary to complete the mathematical model with the receiver's orientation in space. This orientation is given by three angles obtained by the IMU. Finally, the use of GNSS+IMU allows for the complete determination of the receiver's pose (position and orientation), which offers the main advantage of measuring with a tilted pole.

It is important to remember that an IMU is an array of accelerometers and gyroscopes that very precisely determine acceleration and angular velocity, respectively. In general terms, the operation of a GNSS+IMU is redundant. Thanks to the determination of acceleration, it is possible to calculate displacement over time (or position). This, in combination with GNSS, allows the accelerometer to couple to the last precise position determined by the GNSS and achieve a trajectory where GNSS cannot function, or to complement the positioning. On the other hand, the gyroscope does exactly the same through the observation of angular velocity: it determines orientations (or angles) in the three axes over time, which completes the 6 parameters that identify the receiver's pose.


Trimble R12i tilted
(Courtesy of Rumbos Geomensura)

 


Another interesting way to view pole tilt is to search for a more favorable satellite window. For example, if a point needs to be measured at the foot of a slope, tilting the receiver improves the satellite window compared to a vertical position.



Trimble Inertial Platform


Accuracy specification

According to the manufacturer, for a baseline shorter than 30 km, the following accuracy is achieved:

  • Horizontal: 8 mm + 1 ppm
  • Vertical: 15 mm + 1 ppm

 

Horizontal and vertical accuracy (mm)  vs. RTK baseline distance (km)

 

This accuracy is the basis for adding the TIP specification: 

  • RTK + 3 mm + 0.15mm/° (horizontal accuracy)

 

TIP horizontal accuracy (mm) vs. tilt (°)

 

Practical experience

A Trimble R12i receiver, operating with firmware 6.43, was tested, receiving CMRx corrections from an Alloy reference station via the internet. A static observation was made at the beginning and end of the experience to have a reference for comparing the different positions determined over time.

 

Origin point for comparison determined via two static baselines

 

In this way, the same point is observed 5 times in rounds every 15 minutes: one with the pole almost vertical and the rest with the pole tilted, approximately, in the north, east, south, and west directions. Thus, a total of 120 points are observed throughout the entire experience.

 

All points observed via RTK

 

In this way, a standard deviation of 15 mm horizontally and 11 mm vertically is achieved, ensuring repeatability in the solution over time.

 

 

0 comments