@signalk/nmea0183-signalk/hooks/seatalk/0x50.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')

/*
50  Z2  XX  YY  YY  LAT position: XX degrees, (YYYY & 0x7FFF)/100 minutes
                     MSB of Y = YYYY & 0x8000 = South if set, North if cleared
                     Z= 0xA or 0x0 (reported for Raystar 120 GPS), meaning unknown
                     Stable filtered position, for raw data use command 58
                     Corresponding NMEA sentences: RMC, GAA, GLL
*/

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

  var Z = (parseInt(parts[1], 16) & 0xf0) >> 4
  var XX = parseInt(parts[2], 16)
  var YYYY = parseInt(parts[3], 16) + 256 * parseInt(parts[4], 16)
  var s = 1
  if ((YYYY & 0x8000) != 0) {
    s = -1
  }
  var minutes = (YYYY & 0x7fff) / 100.0
  session['latitude'] = s * (XX + minutes / 60)

  var pathValues = []

  if (
    session.hasOwnProperty('latitude') &&
    session.hasOwnProperty('longitude')
  ) {
    pathValues.push({
      path: 'navigation.position',
      value: {
        longitude: utils.float(session['longitude']),
        latitude: utils.float(session['latitude']),
      },
    })
  }

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