#### Positioning Sensor Setup

| Menu path |
|-------------|
| {{ menu }} → {{ settings }} → Sensors → Add sensor → Position |

The sensor connection and setup are performed in accordance with the {doc}`procedure </sections/sensors/navigation-sensors/index>`.

The source of coordinates can be the integrated navigation system {doc}`**INS** </sections/sensors/ins/index>`.

ECDIS accounts for the GNSS antenna position relative to CCRP, therefore the GNSS antenna position in the ship's coordinate system must be specified.

Ensure that received message processing is correctly configured in the sensor settings, i.e., processing of the corresponding headers and message types is enabled.

Some standard navigation data sentences may not include a checksum value in the transmitted data packet. A variant of incorrect checksum calculation by the **GNSS (Global Navigation Satellite System)** receiver is also possible.

To receive such data, ECDIS **can** verify or ignore the checksum (**CRC — cyclic redundancy check**) in incoming sentences.

**CRC verification settings:**

- **Verification disabled** — all sentences will be considered valid
- **Verification enabled** — only sentences that pass verification successfully will be processed

GNSS receivers work with multiple **satellite navigation systems (SNS)**. Each SNS transmits data with a unique sentence header:

- **GN** — Global navigation satellite system (GNSS);
- **GL** — GLONASS positioning system;
- **GP** — Global positioning system (GPS);
- **GA** — Galileo positioning system;
- **GB** — BeiDou positioning system;
- **GI** — IRNSS positioning system;
- **GQ** — QZSS positioning system;
- **SN** — Electronic positioning system, other/general;
- **IN** — Integrated navigation system.

##### Recommended Sentence Set for GNSS Receiver
![Sentences](images/GNSS_2.png)

```{important}
In ECDIS, it is possible to select sentences from any GNSS or from all simultaneously (see list above); to do this, configure the sentence filter by header. See section {doc}`**Navigation Sensors (Sensors).** </sections/sensors/navigation-sensors/index>`
```

```{important}
ECDIS system time is synchronized with **UTC (Coordinated Universal Time)** received from GNSS in the `$--ZDA` sentence each time ECDIS is started, and thereafter when the discrepancy between system time and received time exceeds 5 seconds.

If time synchronization data integrity is compromised, the current ECDIS computer system time is used in calculations until the time source is restored. The navigator cannot change the system time.
```
