crossing

The python package crossing implements the optimisation of the crossing point for the Dijkstra path construction using the NewtonianDistance class. In the section below we will go through, stage by stage, how the crossing point is determined and the methods used within the class.

NewtonianDistance(node_id, neighbour_id, cellboxes, case=None, unit_shipspeed='km/hr', time_unit='days', maxiter=1000, optimizer_tol=0.001)

Class that uses the Newton method to find the crossing point between cells based on their environmental parameters.

Parameters:

Name	Type	Description	Default
node_id	str	the id of the initial cellbox	required
neighbour_id	str	the id of the neighbouring cellbox	required
cellboxes	dict	a dictionary with all cellboxes in the mesh indexed by their ids	required
case	int	the case between the cellboxes	None
unit_shipspeed	str	the speed unit to use	'km/hr'
time_unit	str	the time unit to use	'days'
maxiter	int	the maximum number of iterations for the optimisation	1000
optimizer_tol	float	the tolerance value for the optimisation	0.001

value()

Applying a correction to determine the optimal crossing point between the start and end cell boxes

All outputs are given in SI units (m,m/s,s)

Outputs

Traveltime (tuple,[float,float]) - Traveltime legs from start cell centre to crossing to end cell centre cross_points (tuple,[float,float]) - Crossing Point in (long,lat) cell_points (tuple,[int,int]) - Start and End cell indices Case (int) - Adjacent cell-box case between start and end cell box

waypoint_correction(Wp, Cp)

Determines the traveltime between two points within a given cell Args: Wp (tuple): Start Waypoint location (long,lat) Cp (tuple): End Waypoint location (long,lat) Returns: traveltime (float) - Traveltime between the two points within cell in unit_time

traveltime_in_cell(xdist, ydist, u, v, s, tt_dist=None)

Determine the traveltime within a cell

Parameters:

Name	Type	Description	Default
xdist	float	Longitude distance between two points in km	required
ydist	float	Latitude distance between two points in km	required
u	float	U-Component for the forcing vector	required
v	float	V-Component for the forcing vector	required
s	float	Speed of the vehicle	required
tt_dist	bool	Returns traveltime and distance if true, otherwise just traveltime	None

Returns: traveltime (float): the travel time within the cell dist (float): the distance within the cell