proj4js/lib/apply_gridshift.js

var common = require('./common');
module.exports = function(srs, inverse, point) {
  var i, l, gi, ct, epsilon;
  if (srs.grids === null || srs.grids.length === 0) {
    return -38; //are these error codes?
  }
  var input = {
    "x": point.x,
    "y": point.y
  };
  var output = {
    "x": Number.NaN,
    "y": Number.NaN
  };
  /* keep trying till we find a table that works */
  var onlyMandatoryGrids = false;
  for (i = 0, l = srs.grids.length; i < l; i++) {
    gi = srs.grids[i];
    onlyMandatoryGrids = gi.mandatory;
    ct = gi.grid;
    if (ct === null) {
      if (gi.mandatory) {
        this.reportError("unable to find '" + gi.name + "' grid.");
        return -48; //are these error codes?
      }
      continue; //optional grid
    }
    /* skip tables that don't match our point at all.  */
    epsilon = (Math.abs(ct.del[1]) + Math.abs(ct.del[0])) / 10000;
    if (ct.ll[1] - epsilon > input.y || ct.ll[0] - epsilon > input.x || ct.ll[1] + (ct.lim[1] - 1) * ct.del[1] + epsilon < input.y || ct.ll[0] + (ct.lim[0] - 1) * ct.del[0] + epsilon < input.x) {
      continue;
    }
    /* If we have child nodes, check to see if any of them apply. */
    /* TODO : only plain grid has been implemented ... */
    /* we found a more refined child node to use */
    /* load the grid shift info if we don't have it. */
    /* TODO : ..grids pre-loaded (as they can be huge ...) */
    /* skip numerical computing error when "null" grid (identity grid): */
    if (gi.name === "null") {
      output.x = input.x;
      output.y = input.y;
    }
    else {
      output = common.nad_cvt(input, inverse, ct);
    }
    if (!isNaN(output.x)) {
      break;
    }
  }
  if (isNaN(output.x)) {
    if (!onlyMandatoryGrids) {
      this.reportError("failed to find a grid shift table for location '" + input.x * common.R2D + " " + input.y * common.R2D + " tried: '" + srs.nadgrids + "'");
      return -48;
    }
    return -1; //FIXME: no shift applied ...
  }
  point.x = output.x;
  point.y = output.y;
  return 0;
};