@jbroll/nmea-simple/codecs/DTM.ts

NMEA 0183 sentence parser and encoder

/*
 * === DTM - Datum reference ===
 *
 * ------------------------------------------------------------------------------
 *           1  2  3   4  5   6  7  8    9
 *           |  |  |   |  |   |  |  |    |
 *  $ --DTM,ref,x,llll,c,llll,c,aaa,ref*hh<CR><LF>
 * ------------------------------------------------------------------------------
 *
 * Field Number:
 * 1. Local datum code.
 *    W84 - WGS84
 *    W72 - WGS72
 *    S85 - SGS85
 *    P90 - PE90
 *    999 - User defined IHO datum code
 * 2. Local datum subcode. May be blank.
 * 3. Latitude offset (minutes)
 * 4. N or S
 * 5. Longitude offset (minutes)
 * 6. E or W
 * 7. Altitude offset in meters
 * 8. Datum name. What’s usually seen here is "W84", the standard WGS84 datum used by GPS.
 * 9. Checksum
 */


import { parseFloatSafe, parseLatitude, parseLongitude } from "../helpers";
import { initStubFields, PacketStub } from "./PacketStub";


export const sentenceId: "DTM" = "DTM";
export const sentenceName = "Datum reference";

/**
 * Local datum code (xxx):
 * W84 = WGS84
 * W72 = WGS72
 * S85 = SGS85
 * P90 = PE90
 * 999 = User defined IHO datum code
 */
export type DatumCode = "W84" | "W72" | "S85" | "P90" | "999" | "";


export interface DTMPacket extends PacketStub<typeof sentenceId> {
    datumCode: DatumCode;
    datumSubcode?: string;
    offsetLatitude: number;
    offsetLongitude: number;
    offsetAltitudeMeters: number;
    datumName: DatumCode;
}


export function decodeSentence(stub: PacketStub, fields: string[]): DTMPacket {
    return {
        ...initStubFields(stub, sentenceId, sentenceName),
        datumCode: parseDatumCode(fields[1]),
        datumSubcode: fields[2] || undefined,
        offsetLatitude: parseLatitude(fields[3], fields[4]),
        offsetLongitude: parseLongitude(fields[5], fields[6]),
        offsetAltitudeMeters: parseFloatSafe(fields[7]),
        datumName: parseDatumCode(fields[8])
    };
}


function parseDatumCode(field: string): DatumCode {
    return field === "W84" ? "W84"
        : field === "W72" ? "W72"
        : field === "S85" ? "S85"
        : field === "P90" ? "P90"
        : field === "999" ? "999"
        : "";
}