Coastal express

Compute nearest neighbor distances along the coast with a view angle.

Installation

$ pip install cx

Example

$ cx --boundary="$PWD/boundary.txt" \
     --islands="$PWD/islands.txt" \
     --view-angle=90.0 \
     --min-distance=3.0 \
     --max-distance=40.0 \
     --output-dir="$PWD/output"

Available options

$ cx --help

Usage: cx [OPTIONS]

Options:
  --boundary TEXT      File containing the boundary.
  --islands TEXT       File(s) containing island data - you can use wildcards.
  --view-angle TEXT    View angle in degrees.
  --min-distance TEXT  Min distance.
  --max-distance TEXT  Max distance.
  --output-dir TEXT    Output folder.
  --help               Show this message and exit.

Definition of the view angle

The code will form view vectors perpendicular to the coastline. The code will make sure that along the boundary, the vectors point towards "inside" and along islands they point towards "outside". The view vector is computed to be perpendicular to the vector connecting the two neighboring points of the current point.

The view angle of N degrees defines a view sector N/2 degrees to both sides of the view vector. In other words a view angle of N degrees is N degrees wide in total and is oriented symmetrically around the view vector which is perpendicular to the coast line.

Input and output formats

The code will read boundary and island files. It assumes that the first line in the boundary file contains the total number of polygon points, followed by one line per point. First and last polygon point are expected to be the same point. Two first numbers in each line are assumed to be x and y coordinates in arbitrary but consistent units. Each line can contain more numbers and the code will not worry about these.

The code can read one or many island files. Each island file can contain one or many polygons. Each polygon starts with one line specifying the total number of points. First and last polygon point are expected to be the same point. Each point line is interpreted the same way as the boundary.

The output format preserves all lines and numbers and the only thing it will do is to append each point line by the computed distance. In other words each point line will become longer by one number.