In **AISdb**, the speed of a vessel is calculated using the `aisdb.gis.delta_knots`

function, which computes the *speed over ground (SOG)* in knots between consecutive positions within a given track. This calculation is important for the denoising encoder, as it compares the vessel's speed against a set threshold to aid in the data cleaning process.

Vessel speed calculation requires the **distance** the vessel has traveled between two consecutive positions and the **time interval**. This distance is computed using the haversine distance function, and the time interval is simply the difference in timestamps between the two consecutive AIS position reports. The speed is then computed using the formula:

$Speed(knot) = \frac{Haversine Distance}{Time} \times 1.9438445$

The factor `1.9438445`

converts the speed from meters per second to knots, the standard speed unit used in maritime contexts.

With the example track we created in *Haversine Distance*, we can calculate the vessel speed between each two consecutive positions: