Web page freezing on executing of script

[noelmas]

Web page freezes on execution of script for converting OSGR coordinates to lat/long. Worked on one occasion, now freezes. Also appeared to create duplicate projects on one attempt. Dataset possibly too large.

Data: http://explorer.okfnlabs.org/#noelmas/5f2bf36b37418bcf5ff8/view/grid

Script: // ============================================================ // Library stuff // // For real "meat" see loadDataset function below

// From http://www.movable-type.co.uk/scripts/latlong-convert-coords.html var CoordTransform = {}; // CoordTransform namespace, representing static class

function toRad(num) { // convert degrees to radians return num * Math.PI / 180; }

// ellipse parameters CoordTransform.ellipse = { WGS84: { a: 6378137, b: 6356752.3142, f: 1/298.257223563 }, GRS80: { a: 6378137, b: 6356752.314140, f: 1/298.257222101 }, Airy1830: { a: 6377563.396, b: 6356256.910, f: 1/299.3249646 }, AiryModified: { a: 6377340.189, b: 6356034.448, f: 1/299.32496 }, Intl1924: { a: 6378388.000, b: 6356911.946, f: 1/297.0 } };

// helmert transform parameters from WGS84 to other datums CoordTransform.datumTransform = { toOSGB36: { tx: -446.448, ty: 125.157, tz: -542.060, // m rx: -0.1502, ry: -0.2470, rz: -0.8421, // sec s: 20.4894 }, // ppm toED50: { tx: 89.5, ty: 93.8, tz: 123.1, // m rx: 0.0, ry: 0.0, rz: 0.156, // sec s: -1.2 }, // ppm toIrl1975: { tx: -482.530, ty: 130.596, tz: -564.557, // m rx: -1.042, ry: -0.214, rz: -0.631, // sec s: -8.150 } }; // ppm // ED50: og.decc.gov.uk/en/olgs/cms/pons_and_cop/pons/pon4/pon4.aspx // strictly, Ireland 1975 is from ETRF89: qv // www.osi.ie/OSI/media/OSI/Content/Publications/transformations_booklet.pdf // www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsinfo/guidecontents/guide6.html#6.5

/**

• Convert lat/lon point in OSGB36 to WGS84 *
• @param {LatLon} pOSGB36: lat/lon in OSGB36 reference frame
• @return {LatLon} lat/lon point in WGS84 reference frame */ CoordTransform.convertOSGB36toWGS84 = function(pOSGB36) { var eAiry1830 = CoordTransform.ellipse.Airy1830; var eWGS84 = CoordTransform.ellipse.WGS84; var txToOSGB36 = CoordTransform.datumTransform.toOSGB36; var txFromOSGB36 = {}; // negate the 'to' transform to get the 'from' for (var param in txToOSGB36) txFromOSGB36[param] = -txToOSGB36[param]; var pWGS84 = CoordTransform.convertEllipsoid(pOSGB36, eAiry1830, txFromOSGB36, eWGS84); return pWGS84; }

/**

• Convert lat/lon from one ellipsoidal model to another *
• q.v. Ordnance Survey 'A guide to coordinate systems in Great Britain' Section 6
• www.ordnancesurvey.co.uk/oswebsite/gps/docs/A_Guide_to_Coordinate_Systems_in_Great_Britain.pdf *
• @private
• @param {LatLon} point: lat/lon in source reference frame
• @param {Number[]} e1: source ellipse parameters
• @param {Number[]} t: Helmert transform parameters
• @param {Number[]} e1: target ellipse parameters

• @return {Coord} lat/lon in target reference frame */ CoordTransform.convertEllipsoid = function(point, e1, t, e2) {

  // -- 1: convert polar to cartesian coordinates (using ellipse 1)

  var lat = toRad(point.lat); var lon = toRad(point.lon);

  var a = e1.a, b = e1.b;

  var sinPhi = Math.sin(lat); var cosPhi = Math.cos(lat); var sinLambda = Math.sin(lon); var cosLambda = Math.cos(lon); var H = 24.7; // for the moment

  var eSq = (a_a - b_b) / (a_a); var nu = a / Math.sqrt(1 - eSq_sinPhi*sinPhi);

  var x1 = (nu+H) * cosPhi * cosLambda; var y1 = (nu+H) * cosPhi * sinLambda; var z1 = ((1-eSq)nu + H) \ sinPhi;

  // -- 2: apply helmert transform using appropriate params

  var tx = t.tx, ty = t.ty, tz = t.tz; var rx = toRad(t.rx/3600); // normalise seconds to radians var ry = toRad(t.ry/3600); var rz = toRad(t.rz/3600); var s1 = t.s/1e6 + 1; // normalise ppm to (s+1)

  // apply transform var x2 = tx + x1_s1 - y1_rz + z1_ry; var y2 = ty + x1_rz + y1_s1 - z1_rx; var z2 = tz - x1_ry + y1_rx + z1*s1;

  // -- 3: convert cartesian to polar coordinates (using ellipse 2)

  a = e2.a, b = e2.b; var precision = 4 / a; // results accurate to around 4 metres

  eSq = (a_a - b_b) / (a_a); var p = Math.sqrt(x2_x2 + y2y2); var phi = Math.atan2(z2, p(1-eSq)), phiP = 2_Math.PI; while (Math.abs(phi-phiP) > precision) { nu = a / Math.sqrt(1 - eSq_Math.sin(phi)_Math.sin(phi)); phiP = phi; phi = Math.atan2(z2 + eSq_nu*Math.sin(phi), p); } var lambda = Math.atan2(y2, x2); H = p/Math.cos(phi) - nu;

  return {lat: toDeg(phi), lon: toDeg(lambda)}; }

// taken from http://www.movable-type.co.uk/scripts/latlong-gridref.html /**

• Convert Ordnance Survey grid reference easting/northing coordinate to (OSGB36) latitude/longitude *
• @param {OsGridRef} easting/northing to be converted to latitude/longitude

• @return {LatLon} latitude/longitude (in OSGB36) of supplied grid reference */ function osGridToOSGB36(easting, northing) { var E = easting; var N = northing;

  var a = 6377563.396, b = 6356256.910; // Airy 1830 major & minor semi-axes var F0 = 0.9996012717; // NatGrid scale factor on central meridian var lat0 = 49_Math.PI/180, lon0 = -2_Math.PI/180; // NatGrid true origin var N0 = -100000, E0 = 400000; // northing & easting of true origin, metres var e2 = 1 - (b_b)/(a_a); // eccentricity squared var n = (a-b)/(a+b), n2 = n_n, n3 = n_n*n;

  var lat=lat0, M=0; do { lat = (N-N0-M)/(a*F0) + lat;

  var Ma = (1 + n + (5/4)_n2 + (5/4)_n3) * (lat-lat0); var Mb = (3_n + 3_n_n + (21/8)_n3) * Math.sin(lat-lat0) * Math.cos(lat+lat0); var Mc = ((15/8)_n2 + (15/8)n3) * Math.sin(2(lat-lat0)) * Math.cos(2_(lat+lat0)); var Md = (35/24)n3 * Math.sin(3(lat-lat0)) * Math.cos(3(lat+lat0)); M = b * F0 \ (Ma - Mb + Mc - Md); // meridional arc

  } while (N-N0-M >= 0.00001); // ie until < 0.01mm

  var cosLat = Math.cos(lat), sinLat = Math.sin(lat); var nu = a_F0/Math.sqrt(1-e2_sinLat_sinLat); // transverse radius of curvature var rho = aF0(1-e2)/Math.pow(1-e2_sinLat*sinLat, 1.5); // meridional radius of curvature var eta2 = nu/rho-1;

  var tanLat = Math.tan(lat); var tan2lat = tanLat_tanLat, tan4lat = tan2lat_tan2lat, tan6lat = tan4lat_tan2lat; var secLat = 1/cosLat; var nu3 = nu_nu_nu, nu5 = nu3_nu_nu, nu7 = nu5_nu_nu; var VII = tanLat/(2_rho_nu); var VIII = tanLat/(24_rhonu3)(5+3_tan2lat+eta2-9_tan2lat_eta2); var IX = tanLat/(720_rhonu5)(61+90_tan2lat+45_tan4lat); var X = secLat/nu; var XI = secLat/(6nu3)(nu/rho+2_tan2lat); var XII = secLat/(120nu5)(5+28_tan2lat+24_tan4lat); var XIIA = secLat/(5040nu7)(61+662_tan2lat+1320_tan4lat+720_tan6lat);

  var dE = (E-E0), dE2 = dE_dE, dE3 = dE2_dE, dE4 = dE2_dE2, dE5 = dE3_dE2, dE6 = dE4_dE2, dE7 = dE5_dE2; lat = lat - VII_dE2 + VIII_dE4 - IX_dE6; var lon = lon0 + X_dE - XI_dE3 + XII_dE5 - XIIA*dE7;

  lat = lat * 180 / Math.PI; lon = lon * 180 / Math.PI;

  return {lat: lat, lon: lon}; }

function toDeg(num) { return num * 180 / Math.PI; }

// ============================================= // Our main function where we use the library to transform the data

loadDataset("original", function (error, dataset) { // error will be null unless there is an error // dataset is a Recline memory store (http://reclinejs.com//docs/src/backend.memory.html). // console.log(dataset); dataset.fields.splice(3, 0, {id: 'Latitude'}); dataset.fields.splice(3, 0, {id: 'Longitude'}); dataset.records = dataset.records.map(function(rec) { var out = transform(rec.Location_Easting_OSGR, rec.Location_Northing_OSGR); rec.Latitude = out.lat; rec.Longitude = out.lon; return rec; }); saveDataset(dataset); });

function transform(easting, northing) { var out = osGridToOSGB36(easting, northing); out = CoordTransform.convertOSGB36toWGS84(out); // console.log(out); return out; }

[noelmas]

Above problem was appearing in Google Chrome, also tried in Firefox, kept telling me the script was unresponsive.

[rufuspollock]

@noelmas it will be slow to load on that much data but looks like it has worked - when i look at http://explorer.okfnlabs.org/#noelmas/5f2bf36b37418bcf5ff8/view/grid there is 104210 records and they all seem to be convered. Note you can download the complete csv using the link at the top right called "Data"

[noelmas]

Great, looks like it did complete. I assume the script continues to run even if you close your browser? That would be useful info to have for people working with larger datasets.

[rufuspollock]

@noelmas in theory it should not continue to run if you close that window - but it does run in the background.

[rufuspollock]

INVALID.