@signalk/nmea0183-signalk/hooks/RMC.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')
const moment = require('moment-timezone')

/*
RMC Sentence
http://www.gpsinformation.org/dale/nmea.htm#RMC
$GPRMC,123519,A,4807.038,N,01131.000,E,022.4,084.4,230394,003.1,W*6A
values:
 -      RMC          Recommended Minimum sentence C
[0]     123519       Fix taken at 12:35:19 UTC
[1]     A            Status A=active or V=Void.
[2][3]  4807.038,N   Latitude 48 deg 07.038' N
[4][5]  01131.000,E  Longitude 11 deg 31.000' E
[6]     022.4        Speed over the ground in knots
[7]     084.4        Track angle in degrees True
[8]     230394       Date - 23rd of March 1994
[9][10] 003.1,W      Magnetic Variation
 -      *6A          The checksum data, always begins with *
*/

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

  let latitude = null
  let longitude = null
  let speed = null
  let track = null
  let variation = null

  const timestamp = utils.timestamp(parts[0], parts[8])
  const age = moment.tz(timestamp, 'UTC').unix()

  latitude = parts[2].trim().length > 0 && !isNaN(parts[2]) && "NS".includes(parts[3]) ? utils.coordinate(parts[2], parts[3]) : null
  longitude = parts[4].trim().length > 0 && !isNaN(parts[4]) && "EW".includes(parts[5]) ? utils.coordinate(parts[4], parts[5]) : null

  speed = parts[6].trim().length > 0 && !isNaN(parts[6]) && parts[6] >= 0 ? utils.transform(parts[6], 'knots', 'ms') : null

  track = parts[7].trim().length > 0 && !isNaN(parts[7]) ? utils.transform(parts[7], 'deg', 'rad') : null

  variation = parts[9].trim().length > 0 && !isNaN(parts[9]) && "EW".includes(parts[10]) ? utils.transform(utils.magneticVariaton(parts[9], parts[10]), 'deg', 'rad') : null

  const delta = {
    updates: [
      {
        source: tags.source,
        timestamp: timestamp,
        values: [
          {
            path: 'navigation.position',
            value: {
              longitude,
              latitude,
            },
          },

          {
            path: 'navigation.courseOverGroundTrue',
            value: track,
          },

          {
            path: 'navigation.speedOverGround',
            value: speed,
          },

          {
            path: 'navigation.magneticVariation',
            value: variation,
          },

          {
            path: 'navigation.magneticVariationAgeOfService',
            value: age,
          },

          {
            path: 'navigation.datetime',
            value: timestamp,
          },
        ],
      },
    ],
  }

  return delta
}