proj4js/lib/transform.js

var D2R = 0.01745329251994329577;
var R2D = 57.29577951308232088;
var PJD_3PARAM = 1;
var PJD_7PARAM = 2;
var datum_transform = require('./datum_transform');
var adjust_axis = require('./adjust_axis');
var proj = require('./Proj');
var toPoint = require('./common/toPoint');
module.exports = function transform(source, dest, point) {
  var wgs84;
  if (Array.isArray(point)) {
    point = toPoint(point);
  }
  function checkNotWGS(source, dest) {
    return ((source.datum.datum_type === PJD_3PARAM || source.datum.datum_type === PJD_7PARAM) && dest.datumCode !== "WGS84");
  }

  // Workaround for datum shifts towgs84, if either source or destination projection is not wgs84
  if (source.datum && dest.datum && (checkNotWGS(source, dest) || checkNotWGS(dest, source))) {
    wgs84 = new proj('WGS84');
    transform(source, wgs84, point);
    source = wgs84;
  }
  // DGR, 2010/11/12
  if (source.axis !== "enu") {
    adjust_axis(source, false, point);
  }
  // Transform source points to long/lat, if they aren't already.
  if (source.projName === "longlat") {
    point.x *= D2R; // convert degrees to radians
    point.y *= D2R;
  }
  else {
    if (source.to_meter) {
      point.x *= source.to_meter;
      point.y *= source.to_meter;
    }
    source.inverse(point); // Convert Cartesian to longlat
  }
  // Adjust for the prime meridian if necessary
  if (source.from_greenwich) {
    point.x += source.from_greenwich;
  }

  // Convert datums if needed, and if possible.
  point = datum_transform(source.datum, dest.datum, point);

  // Adjust for the prime meridian if necessary
  if (dest.from_greenwich) {
    point.x -= dest.from_greenwich;
  }

  if (dest.projName === "longlat") {
    // convert radians to decimal degrees
    point.x *= R2D;
    point.y *= R2D;
  }
  else { // else project
    dest.forward(point);
    if (dest.to_meter) {
      point.x /= dest.to_meter;
      point.y /= dest.to_meter;
    }
  }

  // DGR, 2010/11/12
  if (dest.axis !== "enu") {
    adjust_axis(dest, true, point);
  }

  return point;
};