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

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

/**
 * Copyright 2019 Signal K and Fabian Tollenaar <fabian@decipher.industries>.
 *
 * 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/XTE')
const utils = require('@signalk/nmea0183-utilities')

/**
 *        0 1 2   3 4
 *        | | |   | |
 * $--XTE,A,A,x.x,a,N,*hh
 *
 * 0) Status   V = LORAN-C blink or SNR warning
 *             A = general warning flag or other navigation systems when a reliable fix is not available
 *
 * 1) Status   V = Loran-C cycle lock warning flag
 *             A = OK or not used
 *
 * 2) Cross track error magnitude
 * 3) Direction to steer, L or R
 * 4) Cross track units. N = Nautical Miles
 **/

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

  debug(`[XTEHook] decoding sentence ${id} => ${sentence}`)

  if (parts[0].trim().toUpperCase() === 'V') {
    // Don't parse this sentence as it's void.
    throw new Error(
      "Not parsing sentence for it's void (LORAN-C blink/SNR warning)"
    )
  }

  if (parts[1].trim().toUpperCase() === 'V') {
    throw new Error(
      "Not parsing sentence for it's void (LORAN-C cycle warning)"
    )
  }

  if (parts[2].trim() === '' && parts[3].trim() === '') {
    return null
  }

  const direction = parts[3].trim().toUpperCase() === 'L' ? 1 : -1
  const value =
    direction *
    utils.transform(
      parts[2],
      parts[4].trim().toUpperCase() === 'N' ? 'nm' : 'km',
      'm'
    )
  const path = 'navigation.courseRhumbline.crossTrackError'

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