.. chart_datums:
Chart Datums
============
The chart datum is defined using the Lowest Astronomical Tide (LAT) : it is the lowest tide level which can be predicted
to occur under average meteorological conditions and under any combination of astronomical conditions. [LAT]_
The different water height are defined using this chart datum (see :any:`following figure `):
- :math:`B(x,y)` : bathymetry, varying in space,
- :math:`H(t)` : tidal height, given by the tidal model,
- :math:`\eta(x,y,t)` : wave elevation, given by the :any:`wave field model`,
- :math:`H(t)+\eta(x,y,t)` : free surface position, relatively to the LAT,
- :math:`H(t)-B(x,y)` : ocean depth, relatively to the free surface.
.. _heights:
.. figure:: _static/heights.png
:align: center
:alt: chart datums
Chart datum, wave elevation, tidal height and bathymetry definitions
References
----------
.. [LAT] RESOLUTIONS of the INTERNATIONAL HYDROGRAPHIC ORGANIZATION Publication M-3 2nd Edition - 2010 Updated to December 2016. SECTION 2.2 – TIDES AND WATER LEVELS para 2 note (i)