# Seabed

## General

### Depth

The depth of the seabed below the (global) coordinate system origo in ASHES. Must be a positive value.

We recommend that the ASHES coordinate system origo is thought of as the vertical datum. Further we recommend that one of two alternatives chosen when thinking of the zero-level:

ALT 1: Origo is the LAT. A benefit of this is that LAT is the datum of most nautical charts ( see Wikipedia), so depth from such charts can be used directly as the Depth parameter. The Mean sea level (MSL) parameter should then be set to a positive value. Additionally, Tidal level can be used, positive or negative. Since MSL by default is zero, this is the ASHES default.

ALT 2: Origo is MSL. The Depth must then be adjusted (increased) compared to nautical charts. Tidal level can be used with positive or negative values.

To get the actual depth, the parameters for Mean sea level ( MSL) and Tidal level must also be taken into account if any of the two are diffrent from zero. Note that they by default are both zero, so, by default this parameter specifies the actual depth.

Example:

Depth: 20 m. MSL:1.4 m. Tidal level: -1.0m.

The actual depth is: (20.0 + 1.4 - 1.0) m = 20.4 m

• Default value: 20
• Unit: $\text{m}$
• Range: 1 — 10000