@signalk/nmea0183-signalk/hooks/GGA.js

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

'use strict'

/**
 * Copyright 2016 Signal K and Fabian Tollenaar <fabian@signalk.org>.
 *
 * 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.
 */

const debug = require('debug')('signalk-parser-nmea0183/GGA')
const utils = require('@signalk/nmea0183-utilities')
const moment = require('moment-timezone')

/*
=== GGA - Global Positioning System Fix Data ===
Time, Position and fix related data for a GPS receiver.
------------------------------------------------------------------------------
        0         1       2 3        4 5 6  7   8   9 10 11 12  13   14
        |         |       | |        | | |  |   |   | |   | |   |    |
 $--GGA,hhmmss.ss,llll.ll,a,yyyyy.yy,a,x,xx,x.x,x.x,M,x.x,M,x.x,xxxx*hh<CR><LF>
------------------------------------------------------------------------------
Field Number:
0. Universal Time Coordinated (UTC)
1. Latitude
2. N or S (North or South)
3. Longitude
4. E or W (East or West)
5. GPS Quality Indicator,
     - 0 - fix not available,
     - 1 - GPS fix,
     - 2 - Differential GPS fix
           (values above 2 are 2.3 features)
     - 3 = PPS fix
     - 4 = Real Time Kinematic
     - 5 = Float RTK
     - 6 = estimated (dead reckoning)
     - 7 = Manual input mode
     - 8 = Simulation mode
6. Number of satellites in view, 00 - 12
7. Horizontal Dilution of precision (meters)
8. Antenna Altitude above/below mean-sea-level (geoid) (in meters)
9. Units of antenna altitude, meters
10. Geoidal separation, the difference between the WGS-84 earth
     ellipsoid and mean-sea-level (geoid), '-' means mean-sea-level
     below ellipsoid
11. Units of geoidal separation, meters
12. Age of differential GPS data, time in seconds since last SC104
     type 1 or 9 update, null field when DGPS is not used
13. Differential reference station ID, 0000-1023
14. Checksum
*/

function isEmpty(mixed) {
  return (
    (typeof mixed !== 'string' && typeof mixed !== 'number') ||
    (typeof mixed === 'string' && mixed.trim() === '')
  )
}

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

  const empty = parts.reduce((e, val) => {
    if (isEmpty(val)) {
      ++e
    }
    return e
  }, 0)

  if (empty > 4) {
    return null
  }

  const time = parts[0].indexOf('.') === -1 ? parts[0] : parts[0].split('.')[0]
  const timestamp = utils.timestamp(time, moment.tz('UTC').format('DDMMYY'))

  const quality = [
    'no GPS',
    'GNSS Fix',
    'DGNSS fix',
    'Precise GNSS',
    'RTK fixed integer',
    'RTK float',
    'Estimated (DR) mode',
    'Manual input',
    'Simulator mode',
    'Error',
  ]

  const delta = {
    updates: [
      {
        source: tags.source,
        timestamp: timestamp,
        values: [
          {
            path: 'navigation.position',
            value: {
              longitude: utils.coordinate(parts[3], parts[4]),
              latitude: utils.coordinate(parts[1], parts[2]),
            },
          },
          {
            path: 'navigation.gnss.methodQuality',
            value: quality[utils.int(parts[5])],
          },

          {
            path: 'navigation.gnss.satellites',
            value: utils.int(parts[6]),
          },

          {
            path: 'navigation.gnss.antennaAltitude',
            value: utils.float(parts[8]),
          },

          {
            path: 'navigation.gnss.horizontalDilution',
            value: utils.float(parts[7]),
          },

          {
            path: 'navigation.gnss.geoidalSeparation',
            value: utils.float(parts[11]),
          },

          {
            path: 'navigation.gnss.differentialAge',
            value: utils.float(parts[12]),
          },

          {
            path: 'navigation.gnss.differentialReference',
            value: Number(parts[13]),
          },
        ],
      },
    ],
  }

  const toRemove = []

  delta.updates[0].values.forEach((update, index) => {
    if (
      typeof update.value === 'undefined' ||
      update.value === null ||
      (typeof update.value === 'string' && update.value.trim() === '') ||
      (typeof update.value === 'number' && isNaN(update.value))
    ) {
      toRemove.push(index)
    }
  })

  if (toRemove.length > 0) {
    toRemove.forEach((index) => {
      delta.updates[0].values.splice(index, 1)
    })
  }

  return delta
}