Nowadays a depth delineated in a chart is a static depth based on the chart datum, whereas what the ship navigation
should consider is an instantaneous depth, namely, the sum of the static depth and dynamic tide height. Aim to the
shortage in depth representation, a method to construct an instantaneous depth model based on a grid tidal model and
chart data is proposed. Firstly, a regional grid tide model around China is developed based on the Princeton ocean model
(POM) using "blending" assimilation approach, and the continuous spatial-temporal tide heights are predicted. Secondly,
the tide grids serving for all depths in the chart are determined, the depths are located efficiently in these grids and
corresponding tide heights are obtained. Finally, Instantaneous depths are computed and displayed dynamically.
Experimental results indicate that the proposed method is efficient for dynamic representation of instantaneous depths,
and is also accurate for the representation in wide and plane sea areas.