proj4js/lib/datum.js

var PJD_3PARAM = 1;
var PJD_7PARAM = 2;
var PJD_WGS84 = 4; // WGS84 or equivalent
var PJD_NODATUM = 5; // WGS84 or equivalent
var SEC_TO_RAD = 4.84813681109535993589914102357e-6;

function datum(datumCode, datum_params, a, b, es, ep2) {
  var out = {};
  out.datum_type = PJD_WGS84; //default setting
  if (datumCode && datumCode === 'none') {
    out.datum_type = PJD_NODATUM;
  }

  if (datum_params) {
    out.datum_params = datum_params.map(parseFloat);
    if (out.datum_params[0] !== 0 || out.datum_params[1] !== 0 || out.datum_params[2] !== 0) {
      out.datum_type = PJD_3PARAM;
    }
    if (out.datum_params.length > 3) {
      if (out.datum_params[3] !== 0 || out.datum_params[4] !== 0 || out.datum_params[5] !== 0 || out.datum_params[6] !== 0) {
        out.datum_type = PJD_7PARAM;
        out.datum_params[3] *= SEC_TO_RAD;
        out.datum_params[4] *= SEC_TO_RAD;
        out.datum_params[5] *= SEC_TO_RAD;
        out.datum_params[6] = (out.datum_params[6] / 1000000.0) + 1.0;
      }
    }
  }


  out.a = a; //datum object also uses these values
  out.b = b;
  out.es = es;
  out.ep2 = ep2;
  return out;
}

module.exports = datum;