#### Heading Sensor Operational Features

The vessel heading is displayed in the following interface elements:

- **{doc}`Navigational Panel </sections/graphical-user-interface/navigational-panel/index>`**
- **{doc}`Off-scale Danger Indicators </sections/graphical-user-interface/off-scale-indicators/index>` (Danger Course Indicator)**
- **Log book** in the **{doc}`Standard Position </sections/navigational-log/standard-position/index>` (Track) section**

![Navigation Panel](images/HDG_1.png)

| No. | Field | Description |
|---|---|---|
| 1 | **Heading** | Heading received from the heading sensor. Received from sentences: `$--HDG`, `$--HDT`, `$--THS` |
|   | **HDG** | Navigation parameter name — heading |
|   | **Gyro_Prim** | Name of the sensor providing the data |
| 2 | **Rate of Turn** | Rate of turn received from the heading sensor, if the sensor generates it. Received from sentences: `$--ROT` |
|   | **ROT** | Navigation parameter name |
|   | **Gyro_Prim** | Name of the sensor providing the data |
| 3 | -- | Visual representation of heading on the heading scale of the off-scale danger indicator. Received from sentences: `$--HDG`, `$--HDT`, `$--THS` |

#### Heading Discrepancy

When two or more heading sensors are connected to ECDIS, the discrepancy between the Primary and Secondary sensors will be calculated.

![Misclousure POS](images/HDG_3.png)

| No. | Element | Description |
|---|---|---|
| 1 |  | Primary heading sensor with priority **0** |
| 2 |  | Secondary heading sensor with priority **1** |
| 3 | Discrepancy | Heading discrepancy between Primary and Secondary heading sensors |

```{important}
When **heading sensor data is absent**, the vessel mark on the chart is displayed without heading line indication, and the vessel outline will not be displayed at ENC scale.
```

When heading data is available, the following tasks are performed:

- total drift compensation;
- wind calculation;
- vessel movement with drift calculation and monitoring band construction;
- anchor watch;
- vessel outline construction at chart scale;
- radar image overlay.
<br><br>
#### Heading Sensor Warnings

Operating mode messages (rows 2-5 of the table) are generated based on the **Mode indicator** field value in the **THS** message.

| TEXT | CATEGORY | CONDITION |
|---|---|---|
| Heading sensor error: \<sensor name\> | Warning | When data from the sensor stops being received according to the configurable timeout. |
| Simulation mode: \<sensor name\> | Warning | **Mode indicator** field has value **S** — simulation mode. |
| Dead reckoning mode: \<sensor name\> | Warning | **Mode indicator** field has value **E** — dead reckoning mode. |
| Manual heading input: \<sensor name\> | Warning | **Mode indicator** field has value **M** — manual input. |
| Heading sensor data invalid: \<sensor name\> | Warning | **Mode indicator** field has value **V** — data unreliable. |
| Magnetic variation unknown: \<sensor name\> | Warning | Unable to obtain or calculate true heading. The **HDG** message is used for calculations and heading display in the system, but magnetic variation data is absent. |
