# Tech Chat - How Does A GNSS Receiver Implement Tilt Surveying?

As the saying goes, "Science and technology constitute a primary productive force". From my experience as a surveyor over the past few years, I totally agree with this.

I remember that when I was doing surveying work a few years ago, in addition to operating the machine, another key role was centering the range pole. No matter total station or RTK receiver, it is necessary to keep the pole bubble in the center for a measurement. At that time, in fact, it's very tiring for the whole day of survey work. You may have the same idea as me - Can we do the measurement without centering the bubble?

With the technology improved and now we get the answer of "Yes!" on RTK devices.

**Tilt Survey**

As all surveyors know, what we want to get is the ground point coordinates. So when measuring with a range pole, it is necessary to keep the pole centered and fix the pole exactly at the point. Then we can just subtract the pole height to get the correct coordinates of the ground point.

For tilt surveying, how do we calculate the point coordinates from the RTK receiver coordinates? Except for the pole height, it still needs the tilt degree and tilt azimuth. Then we can easily calculate the tilt offset on N/E/H directions via mathematical formula (Pythagorean Theorem) and finally get the correct ground point coordinate.

The key step is how we can get the accurate tilt degree and azimuth, there are mainly two solutions. One is to use a magnetometer sensor, and the other is to use an IMU module. Since the magnetometer sensor is susceptible to magnetic field interference, the accuracy is unstable, especially when near metal objects. So now most RTK brands are using IMU technology for tilt measurement.

**What is IMU?**

IMU (Inertial Measurement Unit) is one of the common sensors to provide motion data in a time-series format, it contains an accelerometer sensor and a gyroscope sensor.

As we all know, the sensors need to be calibrated to maintain high accuracy and performance.

So when using an IMU RTK, the first step is to calibrate. The procedure for calibrating an IMU module varies depending on the brand and technology used. Some brands have complicated steps, while some only require one step.

As a professional GNSS RTK receiver provider, our Y1 IMU GNSS Receiver has a build-in IMU sensor for the tilt surveying, providing centimeter-level accuracy in just one step of calibration.

Watch the IMU calibration video __https://youtu.be/HeOBjQhyvpI__

More about Y1 GNSS receiver

https://www.singularxyz.com/Y1.html

https://www.singularxyz.com/Y1_Land_Surveying_Solution.html