A 100% python weather routing library for sailing.

An introductory explanation (english, french, spanish and italian translations) of weather routing tools and methods can be find in: https://globalsolochallenge.com/weather-routing/

pip install weatherrouting

For a comprehensive usage reference example pleace refer to wind_forecast_routing QGIS plugin or GWeatherRouting standalone application

Almost one external function has to be implemented as a preliminary requirement for library usage:

A function that accept a datetime item, a float latitude and float longitude as parameters, performs a wind forecast analysis for the specified time and location (usually sampling a grib file) and returns a tuple with true wind direction (twd) expressed in radians and true wind speed (tws) expressed in meters per second or None if running out of temporal/geographic grib scope.

def getWindAt( t, lat, lon)
    # wind forecast analysys implementation
    ...
    return (twd, tws)

A function that accept a float latitude and float longitude as parameters, performs a test to check if the specified location is eligible as waypoint (i.e. lay or not on sea) and returns a boolean (True if valid, False if invalid)

def point_validity(lat, lon)
    # 
    ...
    return True/False

A function that accept a vector defined as four float parameters (latitude1, longitude1, latitude2, longitude2) performs a test to check whether the specified line between two waypoints is valid (i.e. lays completely or not on sea, or in other words is in line of sight) and returns a boolean (True if valid, False if invalid)

def line_validity(lat1, lon1, lat1, lon1)
    # 
    ...
    return True/False

from weatherrouting import Routing, Polar
from weatherrouting.routers.linearbestisorouter import LinearBestIsoRouter
from datetime import datetime

Define a list of trackpoints as lat,long tuples (almost 2) that have to be reached by the route

track = ((5.1, 38.1), (5.2, 38.4), (5.7, 38.2))

Define the polar object from a polar file describing the performance of the boat at different wind speeds (tws) and different angles (twd)

polar_obj = Polar("polar_files/bavaria38.pol")

Define the polar object from a polar file describing the performance of the boat at different wind speeds (tws) and different angles (`twd~)

start = datetime.fromisoformat('2021-04-02T12:00:00')

routing_obj = Routing(
    LinearBestIsoRouter,            # specify a router type
    polar_obj,                      # the polar object for a specific sail boat
    track,                          # the list of track points (lat,lon)
    getWindAt,                      # the function that returns (twd,tws) for a specified (datetime, lat, lon)
    start,                          # the start datetime
    start_position = (4.8,37.8)     # the start location (lat lon, optional, the first track point if undefined)
    pointValidity = point_validity  # the point validity function (optional)
    lineValidity = line_validity    # the line validity function (optional)
)

Calculate subsequent steps until the end track point is reached

while not self.routing_obj.end:
    res = self.routing_obj.step()

the step method returns a RoutingResult object with the following informations during routing calculation:

res.time         # the datetime of step  
res.isochrones   # all points reached at a specified datetime
res.progress     # the calculation progress 

and after the end of the routing calculation contains a list of tuple containing the waypoints informations (lat,lon,datetime, twd, tws, speed, heading)

res.path         # the list of route waypoints

The path could be exported as a geojson object for cartographic representation

from weatherrouting.utils import pathAsGeojson
import json

json.dumps(pathAsGeojson(res.path))

Read the LICENSE file.

This work is partially based and inspired by Riccardo Apolloni Virtual Sailing Simulator.