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Coast, shore, and ports

Extracting distance features from and to points-of-interest using raster files.

The distances of a vessel from the nearest shore, coast, and port are essential to perform particular tasks such as vessel behavior analysis, environmental monitoring, and maritime safety assessments. AISdb offers functions to acquire these distances for specific vessel positions. In this tutorial, we provide examples of calculating the distance in kilometers from shore and from the nearest port for a given point.

First, we create a sample track:

import aisdb
from aisdb.gis import dt_2_epoch

y1, x1 = 44.57039426840729, -63.52931373766157
y2, x2 = 44.51304767533133, -63.494075674952555
y3, x3 = 44.458038982492134, -63.535634138077945
y4, x4 = 44.393941339104074, -63.53826396955358
y5, x5 = 44.14245580737021, -64.16608964280064

t1 = dt_2_epoch( datetime(2021, 1, 1, 1) )
t2 = dt_2_epoch( datetime(2021, 1, 1, 2) )
t3 = dt_2_epoch( datetime(2021, 1, 1, 3) )
t4 = dt_2_epoch( datetime(2021, 1, 1, 4) )
t5 = dt_2_epoch( datetime(2021, 1, 1, 7) )

# creating a sample track
tracks_short = [
    dict(
        mmsi=123456789,
        lon=np.array([x1, x2, x3, x4, x5]),
        lat=np.array([y1, y2, y3, y4, y5]),
        time=np.array([t1, t2, t3, t4, t5]),
        dynamic=set(['lon', 'lat', 'time']),
        static=set(['mmsi'])
    )
]

Here is what the sample track looks like:

Distance from shore

The class aisdb.webdata.shore_dist.ShoreDist is used to calculate the nearest distance to shore, along with a raster file containing shore distance data. Currently, calling the get_distance function in ShoreDist will automatically download the shore distance raster file from our server. The function then merges the tracks in the provided track list, creates a new key, "km_from_shore", and stores the shore distance as the value for this key.

from aisdb.webdata.shore_dist import ShoreDist

with ShoreDist(data_dir="./testdata/") as sdist:
        # Getting distance from shore for each point in the track
        for track in sdist.get_distance(tracks_short):
            assert 'km_from_shore' in track['dynamic']
            assert 'km_from_shore' in track.keys()
            print(track['km_from_shore'])

[ 1  3  2  9 14]

Distance from coast

Similar to acquiring the distance from shore, CoastDist is implemented to obtain the distance between the given track positions and the coastline.

from aisdb.webdata.shore_dist import CoastDist

with CoastDist(data_dir="./testdata/") as cdist:
        # Getting distance from the coast for each point in the track
        for track in cdist.get_distance(tracks_short):
            assert 'km_from_coast' in track['dynamic']
            assert 'km_from_coast' in track.keys()
            print(track['km_from_coast'])

[ 1  3  2  8 13]

Distance from port

Like the distances from the coast and shore, the aisdb.webdata.shore_dist.PortDist class determines the distance between the track positions and the nearest ports.

from aisdb.webdata.shore_dist import PortDist

with PortDist(data_dir="./testdata/") as pdist:
        # Getting distance from the port for each point in the track
        for track in pdist.get_distance(tracks_short):
            assert 'km_from_port' in track['dynamic']
            assert 'km_from_port' in track.keys()
            print(track['km_from_port'])

[ 4.72144175  7.47747231  4.60478449 11.5642271  28.62511253]