Generate True Heading from Magnetic Heading

[scurvy-dog]

This simple flow subscribes to navigation.headingMagnetic from SignalK than adds a hard coded value for the magnetic declination for my area. It also transforms the topic from navigation.headingMagnetic to navigation.headingTrue. And last it outputs the data back to SignalK.

[scurvy-dog]

[
{
"id": "95981eba.b644c",
"type": "tab",
"label": "Flow 2",
"disabled": false,
"info": ""
},
{
"id": "4ee3faa1.1a5444",
"type": "change",
"z": "95981eba.b644c",
"name": "Add MagVar",
"rules": [
{
"t": "set",
"p": "payload",
"pt": "msg",
"to": "payload + 0.27",
"tot": "jsonata"
},
{
"t": "set",
"p": "topic",
"pt": "msg",
"to": "navigation.headingTrue",
"tot": "str"
}
],
"action": "",
"property": "",
"from": "",
"to": "",
"reg": false,
"x": 410,
"y": 320,
"wires": [
[
"b2eb0573.d53868"
]
]
},
{
"id": "7aafc0ea.3f107",
"type": "signalk-subscribe",
"z": "95981eba.b644c",
"name": "Heading Magnetic",
"mode": "sendAll",
"flatten": true,
"context": "vessels.self",
"path": "navigation.headingMagnetic",
"source": "",
"period": 1000,
"x": 170,
"y": 320,
"wires": [
[
"4ee3faa1.1a5444"
]
]
},
{
"id": "b2eb0573.d53868",
"type": "signalk-send-pathvalue",
"z": "95981eba.b644c",
"name": "Heading True",
"source": "",
"meta": "",
"x": 660,
"y": 320,
"wires": []
}
]