Bitsailor

Sailing route optimization

Bitsailor uses the well-known Isochrones method for sailing route optimization. This is basically a brute-force algorithm that computes all positions reachable from a given position by moving with constant speed and direction for a fixed amount of time (eg. 10min). The resulting positions are filtered to prevent exponential growth and constitute the next isochrone.

Map

Bitsailor uses geodata provided by FOSSGIS e.V. which in turn uses OpenStreetMap data.

Map data is accessed with libgdal. The 'Land Polygons' file with split polygons from openstreetmapdata is used. A geospatial index is computed off-line on the set of polygons. (The non-split polygons file, while smaller, provides a less selective index and is therefor much slower).

At runtime the index is used to quickly find and intersect polygons with the boat path. In order to improve performance, a 1° tile cache is used . If neither the tile containing the start point nor the tile containing the end point of the path contain any land, the exact land check is skipped.

Wind

Polars

Boat polars are provided as CSV files or in JSON format containing separate array for each sail. Data is interpolated to 0.1 degrees and 0.1 m/s. The resulting arrays are compressed into a single array returning both the best sail and the corresponding speed.

Filtering

Installation

Prerequisites

Install libgdal with GEOS support via apt (package name may vary)
```
$ sudo apt-get install libgdal20
```
or following these instructions. In the latter case first install libgeos-3.4.2 (or newer) and dev files
```
$ sudo apt-get install libgeos-3.5.0
$ sudo apt-get install libgeos-dev
```
Then do
```
$ ./configure --with-geos=yes
```
Check that GEOS support is available.
Download the Land polygons shapefile, WGS84 projection, split polygons from osmdata.openstreetmap.de
```
$ wget https://osmdata.openstreetmap.de/download/land-polygons-split-4326.zip
```
Install package mapserver-bin
```
$ sudo apt-get install mapserver-bin
```

Unpack the shapefile archive. Generate a geospatial index.

$ unzip land-polygons-split-4326.zip
$ cd land-polygons-split-4326.zip
$ shptree land_polygons.shp

In addition, Bitsailor requires

and the quickloadable systems

cl-utilities
cffi
local-time
babel

Links

DWD opendata DWD publicly available weather data (new)

DWD GDS DWD basic public services (old)

GEOS Geometry Engine

GDAL Geospatial Data Abstraction Layer

GDAL Wiki GDAL bug tracker and Wiki

mak08/Bitsailor