This plugin calculates missing data from the data that is supplied to AvNav.
- magnetic variation - is calculated at current position based on the World Magnetic Model.
- true heading - from magnetic heading and variation
- set and drift - from ground track and water track
- depth below surface - from depth below transducer and configured depth of transducer
- true and ground wind - from apparent wind and course data
- TODO: leeway estimation
The formulas used for the calculation are best read directly in the code.
All calculated and input values are available in AvNav under gps.calculated.*. It reads its input data from the AvNav data model, after NMEA parsing hase been done by AvNav.
It also can write NMEA sentences, which are parsed by AvNav itself and are forwarded to NMEA outputs.
With leeway factor
angles and directions are always converted like
The
| quantity | description |
|---|---|
| HDG | heading, unspecified which of the following |
| HDT | true heading, direction bow is pointing to, relative to true north (also HDGt) |
| HDM | magnetic heading, as reported by a calibrated compass (also HDGm) |
| HDC | compass heading, raw reading of the compass (also HDGc) |
| VAR | magnetic variation, given in chart or computed from model |
| DEV | magnetic deviation, boat specific, depends on HDG |
| COG | course over ground, usually from GPS |
| SOG | speed over ground, usually from GPS |
| SET | set, direction of tide/current, cannot be measured directly |
| DFT | drift, rate of tide/current, cannot be measured directly |
| STW | speed through water, usually from paddle wheel, water speed vector projected onto HDT (long axis of boat) |
| HEL | heel angle, measured by sensor or from heel polar TWA/TWS -> HEL |
| LEE | leeway angle, angle between HDT and direction of water speed vector, usually estimated from wind and/or heel and STW |
| CRS | course through water |
| AWA | apparent wind angle, measured by wind direction sensor |
| AWD | apparent wind direction, relative to true north |
| AWS | apparent wind speed, measured by anemometer |
| TWA | true wind angle, relative to water, relative to HDT |
| TWD | true wind direction, relative to water, relative true north |
| TWS | true wind speed, relative to water |
| GWA | ground wind angle, relative to ground, relative to HDT |
| GWD | ground wind direction, relative to ground, relative true north |
| GWS | ground wind speed, relative to ground |
| DBS | depth below surface |
| DBT | depth below transducer |
| DBK | depth below keel |
| DRT | draught |
| DOT | depth of transducer |