TrueWind
Contents
see also
- http://davidburchnavigation.blogspot.com/2013/04/true-true-wind-from-apparent-wind.html
- https://coaps.fsu.edu/woce/truewind/paper/index.html
- http://signalk.org/specification/1.0.0/doc/otherBranches.html
- http://www.catb.org/gpsd/NMEA.html
- https://opencpn.org/wiki/dokuwiki/doku.php?id=opencpn:opencpn_user_manual:terminology
Terms
vessel's Movement and Orientation
- SOG Speed Over Ground navigation.speedOverGround
- COG Course Over Ground (relative to true north) navigation.courseOverGroundTrue
- COG Course Over Ground (relative to magnetic north) navigation.courseOverGroundMagnetic
- STW Speed Trough Water navigation.speedThroughWater
- HDG Heading
- HDT Heading (relative to true north) navigation.headingTrue
- HDM Heading (relative to magnetic north) navigation.headingMagnetic
Wind
- AW Apparent Wind (relative to vessel)
- AWS Apparent Wind Speed environment.wind.speedApparent
- AWD Apparent Wind Direction (relative to true north) environment.wind.directionTrue
- AWD Apparent Wind Direction (relative to magnetic north) environment.wind.directionMagnetic
- AWA Apparent Wind Angle (relative to HDG) environment.wind.angleApparent
- TW True Wind (relative to surface of the water)
- TWS True Wind Speed (relative to water) environment.wind.speedTrue
- TWD True Wind Direction (relative to true north) ???
- TWA True Wind Angle (relative to HDG) environment.wind.angleTrueWater
- GW Ground Wind (relative to ground) used in weather forecasts and reports
- GWS Ground Wind Speed (relative to ground) environment.wind.speedOverGround
- GWD Ground Wind Direction (relative to true north) ???
- GWA Ground Wind Angle (relative to HDG) environment.wind.angleTrueGround
Current
- DFT Current Drift (speed relative to ground) environment.current.drift
- SET Current Set (direction relative to true north) environment.current.setTrue
- SET Current Set (direction relative to magnetic north) environment.current.setMagnetic
calculate True Wind from Apparent Wind
- AWA Apparent Wind Angle (relative to H) environment.wind.angleApparent
- H Heading (relative to true north) navigation.headingTrue
- AWD Apparent Wind Direction (relative to true north) environment.wind.directionTrue
AWD = MOD(H+AWA;360)
- AWS Apparent Wind Speed environment.wind.speedApparent
- COG Course Over Ground navigation.courseOverGroundTrue
- SOG Speed Over Ground navigation.speedOverGround
- TWS True Wind Speed (relative to ground) environment.wind.speedOverGround
TWx = OGx - AWx = SOG * Sin (COG) - AWS * Sin (AWD)TWy = OGy - AWy = SOG * Cos (COG) - AWS * Cos (AWD)TWS= SQRT (TWx*TWx + TWy*TWy)- TWD True Wind Direction (relative to true north) ???
TWD = ATAN ( TWx / TWy )
- S Speed over ground in direction of H
- DFT Drift (speed relative to ground) ???
DFTx = OGx - SHx = SOG * Sin (COG) - S * Sin (H)DFTy = OGy - SHy = SOG * Cos (COG) - S * Cos (H)DFT= SQRT (DFTx*DFTx + DFTy*DFTy)- SET Set (direction relative to true north) ???
SET = ATAN ( DFTx / DFTy )
signalk-derived-data (assuming COG=H)
- https://github.com/SignalK/signalk-derived-data/blob/master/calcs/groundWind.js
- COG Course Over Ground navigation.courseOverGroundTrue
- SOG Speed Over Ground navigation.speedOverGround
- AWA Apparent Wind Angle (relative to H) environment.wind.angleApparent
- AWS Apparent Wind Speed environment.wind.speedApparent
AWx = AWS * Cos (AWA)AWy = AWS * Sin (AWA)- TWA True Wind Angle (relative to H) environment.wind.angleTrueGround
TWA = ATAN2(AWy, -SOG + AWx)- TWS True Wind Speed (relative to ground) environment.wind.speedOverGround
TWS = SQRT (POWER(AWy,2) POWER(-SOG + AWx,2))
Sensors
Heading
- see also http://www.navlab.net/Publications/The_Seven_Ways_to_Find_Heading.pdf
- magnetic compass
- H true = H magnetic + Magnetic declination
- Fluxgate compass
- H true = H magnetic + Magnetic declination
- Gyrocompass
- H true
- moving baseline Real-time kinematic (GPS)
- H true
SOG and COG
- GPS receiver
STW
AWS and AWA
- wind-vane (AWA)
- anemometer
- cup (AWS)
- hand held propeller (AWS)
- ultrasonic (AWS and AWA)
