## Limitations and Recommendations

```{note}
The International Hydrographic Organization notes that any navigational chart adequately reflects the navigational and hydrographic conditions only at the time the hydrographic survey was conducted.
```

Due to the high variability of seabed topography in coastal zones, narrow channels, areas of intense river run-off, as well as the influence of wind-driven and tidal phenomena, **depths may differ from those indicated on the chart**.

### Key limitations when operating ECDIS

#### 1. Reduced accuracy near coasts and structures

When navigating in waters near **high coastlines** or **artificial structures**, GNSS fix accuracy may be significantly reduced due to deterioration of the geometric dilution of precision (GDOP), caused by the inability to observe some satellites.

```{warning}
In some cases, a differential correction may degrade the result of the vessel's position determination.
```

**NSR ECDIS NES-3000 software** automatically monitors the quality of the geometric dilution of precision based on GNSS receiver data and generates a warning signal when the limit value of the integral geometric factor is exceeded.

#### 2. GNSS signal degradation

Due to the low **signal-to-noise ratio** at the GNSS antenna input, cases of signal degradation have been observed while the GNSS receiver continues to output a valid fix flag.

**This manifests as:**
- Displacement of the vessel's position plotted on the ENC
- Visual drift of the vessel under the influence of current

```{tip}
SN Circular 255, issued by the IHO, recommends overlaying the radar image on the electronic chart for timely detection of such situations.
```

#### 3. Recommendations when navigating along leading lines

When navigating along **leading lines**, it is recommended to always compare the plotted position with the leading lines shown on the electronic chart, which allows timely detection of unstable GNSS performance.

#### 4. Specifics of operation during turning manoeuvres

GNSS receivers have a function for **filtering random outliers** of navigational parameters over a series of measurements, which improves the quality of coordinate and speed-over-ground vector computation when sailing on a steady course.

```{important}
During a turning manoeuvre, the vessel's heading changes significantly faster than the course over ground (COG), which is the direction of the velocity vector produced by the GNSS receiver.
```

**For this reason, the results of automatic ECDIS monitoring of charted hazards during a turning manoeuvre should be treated with caution**, since ENC scanning is performed in a strip or sector ahead of the vessel in the direction of the COG, and with a narrow sector part of the water area may remain outside the monitored zone.

### Recommendations for monitoring the vessel's position

In the cases described above, for monitoring the vessel's position relative to navigational hazards and in fairways, use:

- **Aids to navigation (ATON)**
- **Navigational Radar**
- **Do not rely solely on ECDIS readings**


```{important}
NSR ECDIS NES-3000 ensures correct operation and display of ENCs in the latitude range from 85°N to 85°S.
```
