# Navigation System

The navigation system menu contains settings such as IMU orientation, GNSS antenna type, and GNSS antenna lever arm offsets:

<figure><img src="https://2222094320-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdEevfLZRIk38LUPwDa4V%2Fuploads%2FJnLDzvvt6Oic3W9E7fZ5%2Fimage.png?alt=media&#x26;token=7c9f106a-3458-4ebe-8174-574b27d4c45e" alt=""><figcaption></figcaption></figure>

### IMU Orientation

IMU orientation indicates how the IMU axes need to be rotated so that they align with the vehicle axes. Per the Novatel InertialExplorer convention, vehicle axes are: X-vehicle right, Y-vehicle forward, Z-vehicle up. This InertialExplorer definition of vehicle axes is the most relevant as InertialExplorer / NavLab use this definition of the vehicle for trajectory processing. If your IMU orientation is incorrect, it's very likely that trajectory processing will not succeed. &#x20;

To change the IMU Orientation, click **Configure.** The IMU orientation is displayed in many different conventions:

<figure><img src="https://2222094320-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdEevfLZRIk38LUPwDa4V%2Fuploads%2FsTOTbnX80KDM4Dw0QsxW%2Fimage.png?alt=media&#x26;token=cd683550-7ff6-4ab1-a7cf-acb11e3cd77e" alt=""><figcaption></figcaption></figure>

It's recommended to change the IMU orientation using the **Axis Mapping** matrix, to prevent from incorrectly determining X,Y,Z rotations.  More information can be found about IMU orientation [here](https://docs.phoenixlidar.com/hardware-and-interfaces/gnss/orientation-and-offsets/imu).

{% hint style="info" %}
IMU orientation depends not only on the model of the IMU, but also the way the lidar system is installed in respect to the vehicle.&#x20;
{% endhint %}

### GNSS Antennas

**Antenna type**: Indicates the antenna model. If the antenna is not NGS Calibrated, it will not appear in the list - in this case, use the **Generic** antenna model:

<figure><img src="https://2222094320-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdEevfLZRIk38LUPwDa4V%2Fuploads%2FZrI5kp9PKPNkFe6rbeVa%2Fimage.png?alt=media&#x26;token=8d36f90d-f335-4459-b76d-0fb65f627628" alt=""><figcaption></figcaption></figure>

**Antenna lever arm offsets**:

The distance between the IMU and GNSS antenna phase center must be known precisely. The X, Y, Z translations from IMU to antenna, otherwise known as GNSS antenna lever arm measurements, are entered here, along IMU axes:

<figure><img src="https://2222094320-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FdEevfLZRIk38LUPwDa4V%2Fuploads%2FNOVXjf5b2VVhkKUxpcUH%2Fimage.png?alt=media&#x26;token=72fce7ae-83df-421f-81eb-2de345003a42" alt=""><figcaption></figcaption></figure>

If your system utilizes dual antenna functionality, both antennas will require offsets to be entered. More information about GNSS antenna lever arms can be found[ here](https://docs.phoenixlidar.com/hardware-and-interfaces/gnss/orientation-and-offsets/gnss-antennas).

{% hint style="info" %}
Offsets from IMU to antenna are measured along IMU axes. For example, if the IMU's Z axis points down, and the GNSS antenna phase center is 35 cm above the IMU, this would be entered as -0.350 m Z, because a positive Z value in this case is defined as downwards (or vehicle down).&#x20;
{% endhint %}