Analyze sailboat performance data gathered from NMEA-0183 and NMEA-2000 (N2K) data sources
- Analyze sailboat race performance using data collected from NMEA bus
- Compute polar plots, per-leg strip charts, minute-by-minute summaries, and Expedition-ready text
- Generate reports in various formats - text files, graphics, and spreadsheets
It has become very easy and relatively inexpensive to record raw NMEA data, for instance:
- Directly via ~$250 Yacht Devices Voyage Data Recorder
- Indirectly via N2K to WiFi gateways (such as any B&G Zeus or Vulcan MFD, Vesper AIS/WiFi gateways, and Yacht Devices YDWG NMEA-2000 dongles) and apps like SEAiq ($5 for iPhone/USA, $50 for Android/World)
polarize takes this data and converts it to more familiar forms - polar charts, strip charts, track files, spreadsheets, etc.
polarize requires two inputs:
- A list of .json files describing the races and courses in a regatta (typically regatta.json)
- A per-race NMEA data file pointed to from inside the regatta file
- .log files are assumed to have raw N2K data
- .nmea files are assumed to have NMEA-0183 text sentences
The regatta file contains additional information including boat name, timezone offset, rudder correction, and COG/SOG sources. Typically one creates a directory for each regatta since they share courses.
polarize can generate several kinds of output:
| Option | Effect |
|---|---|
| -strip | Create per-race strip graph files |
| -legs | Create per-leg analysis |
| -minute | Create minute-by-minute reports in per-leg analysis |
| -spreadsheet | Create xlsx spreadsheet file |
| -polars | Create aggregate polar graph file |
| -exp | Create aggregate Expedition polar text file |
| -gpx | Create gpx track |
Polars can be generated per-regatta or aggregated from multiple regattas (polarize -polars */regatta.json)
NMEA-0183 .nmea files (i.e. recorded with SEAiq) are parsed directly
NMEA-2000 .log files from Yacht Devices VDR Voyage Data Recorder are converted to JSON by the canboat analyzer (https://www.github.com/canboat/canboat)
It's becoming common for boats to have multiple sources of similar data. For instance COG/SOG data on a boat with a B&G MFD and ZG100 GPS/heading sensor will disagree due to different damping heuristics, sometimes by quite a bit. The N2K Source ID can be specified in the regatta file for N2K data to choose which device to use. If naively converted to NMEA-0183 by a WiFi gateway the source ID field is lost making it hard/impossible to filter for only one source. This may confuse polarize.
polarize requires Python3.x and additional modules:
- matplotlib for plotting (https://matplotlib.org)
- numpy for some statistics (https://numpy.org)
- scipy for Savitsky-Golay filtering (https://scipy.org)
- xlsxwriter to generate Excel-compatible .xlsx files (https://pypi.org/project/XlsxWriter)
polarize requires kludgey internal configuration:
- The ANALYZE variable must point to the local copy of analyze to enable N2K data conversion
- Polar wind ranges are set manually in a table. The default is good for a particular schooner in typical San Francisco Bay wind ranges.
Copyright 2019 Lance Berc
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