@signalk/nmea0183-signalk/hooks/seatalk/0x99.js

A node.js/javascript parser for NMEA0183 sentences. Sentences are parsed to Signal K format.

/**
 * Copyright 2016 Signal K <info@signalk.org> and contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

'use strict'

const utils = require('@signalk/nmea0183-utilities')

/*
99  00  XX        Compass variation sent by ST40 compass instrument
                     or ST1000, ST2000, ST4000+, E-80 every 10 seconds
                     but only if the variation is set on the instrument
                     Positive XX values: Variation West, Negative XX values: Variation East
                     Examples (XX => variation): 00 => 0, 01 => -1 west, 02 => -2 west ...
                                                 FF => +1 east, FE => +2 east ...
                   Corresponding NMEA sentences: RMC, HDG
*/

module.exports = function (input) {
  const { id, sentence, parts, tags } = input

  var XX = parseInt(parts[2], 16)
  var value = 128 - (XX & 0x7f)
  var s = -1
  if (XX & (0x80 != 0)) {
    s = 1
  }
  var magneticVariation = s * value

  var pathValues = []

  pathValues.push({
    path: 'navigation.magneticVariation',
    value: utils.transform(utils.float(magneticVariation), 'deg', 'rad'),
  })

  return {
    updates: [
      {
        source: tags.source,
        timestamp: tags.timestamp,
        values: pathValues,
      },
    ],
  }
}