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

const FEET_TO_METERS = 0.3048

/*
=== DBT - Depth below transducer ===
------------------------------------------------------------------------------
*******0   1 2   3 4   5 6
*******|   | |   | |   | |
$--DBT,x.x,f,x.x,M,x.x,F*hh<CR><LF>
------------------------------------------------------------------------------
Field Number:
0. Depth, feet
1. f = feet
2. Depth, meters
3. M = meters
4. Depth, Fathoms
5. F = Fathoms
6. Checksum
*/

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

  let meterValue = parts[2]

  if (hasNoValue(meterValue)) {
    const feetValue = parts[0]
    if (hasNoValue(feetValue)) {
      meterValue = null
    } else {
      meterValue = utils.float(feetValue) * FEET_TO_METERS
    }
  } else {
    meterValue = utils.float(meterValue)
  }

  const delta = {
    updates: [
      {
        source: tags.source,
        timestamp: tags.timestamp,
        values: [
          {
            path: 'environment.depth.belowTransducer',
            value: meterValue,
          },
        ],
      },
    ],
  }

  return delta
}

const hasNoValue = (value) =>
  (typeof value !== 'string' && typeof value !== 'number') ||
  (typeof value === 'string' && value.trim() === '')