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srs.js
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srs.js
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var path = require('path');
var fs = require('fs');
var srs = require('./_srs');
var _settings = require('./settings');
var exists = require('fs').existsSync || require('path').existsSync;
/*
This is a custom srs definition for
spherical mercator that we make
canonical because no single variant
of the projection stored by various
applications is optimal.
This is basically a modification of gdal's
understanding of epsg 3857
Changes:
* add +over and +wktext to proj4 string
* remove any double spaces in proj4 string
* epsg is 3857, the new official epsg for 900913
* name is pulled from gdal/data/cubwerx_extra.wkt for 900913
instead of using 'WGS 84 / Pseudo-Mercator' or 'Popular...'
TODO:
* +x_0=0.0 vs +x_0=0 (same with +y_0)
* handle two scaling aliases +k and +k_0
* meaning of +k=1. vs +k=1.0 ?
*/
var merc_pretty_wkt = 'PROJCS["WGS 84 / Pseudo-Mercator",\n GEOGCS["WGS 84",\n DATUM["WGS_1984",\n SPHEROID["WGS 84",6378137,298.257223563,\n AUTHORITY["EPSG","7030"]],\n AUTHORITY["EPSG","6326"]],\n PRIMEM["Greenwich",0,\n AUTHORITY["EPSG","8901"]],\n UNIT["degree",0.0174532925199433,\n AUTHORITY["EPSG","9122"]],\n AUTHORITY["EPSG","4326"]],\n UNIT["metre",1,\n AUTHORITY["EPSG","9001"]],\n PROJECTION["Mercator_1SP"],\n PARAMETER["central_meridian",0],\n PARAMETER["scale_factor",1],\n PARAMETER["false_easting",0],\n PARAMETER["false_northing",0],\n EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs"],\n AUTHORITY["EPSG","3857"],\n AXIS["X",EAST],\n AXIS["Y",NORTH]]';
exports.canonical = {
spherical_mercator: {
proj4: '+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0.0 +k=1.0 +units=m +nadgrids=@null +wktext +no_defs +over',
srid: 3857, // or 900913
auth: 'EPSG',
pretty_wkt: merc_pretty_wkt,
esri: false,
name: 'Google Maps Global Mercator', // so many variants here
valid: true,
is_geographic: false
}
};
function oc(a) {
var o = {};
for (var i = 0; i < a.length; i++) {
o[a[i]] = '';
}
return o;
}
var merc_names = [
'Google_Maps_Global_Mercator',
'Google Maps Global Mercator',
'WGS 84 / Pseudo-Mercator', // 3857
'Popular Visualisation CRS / Mercator', // 3785
'WGS_1984_Web_Mercator', // ESRI
'WGS_1984_Web_Mercator_Auxiliary_Sphere', // ESRI
'Popular_Visualisation_CRS_Mercator_deprecated' // wtf
];
var merc_srids = [
900913, // neo-hippy followers of http://crschmidt.net/
3857, // epsg official, second try
3785, // epsg deprecated, failed first try
//3587, // common typo but actually NAD83(NSRS2007) / Michigan Central
102100, // esri official, second try
102113, // esri deprecated, failed first try
41001 //osgeo
];
/*
if we have statically linked libosr then we need
to set the GDAL_DATA directory so that the bundled
.csv and .wkt files are found.
*/
if (_settings.static_osr) {
process.env.GDAL_DATA = path.join(__dirname, 'srs_data');
}
// push all C++ symbols into js module
for (var k in srs) { exports[k] = srs[k]; }
// make settings available
exports.settings = _settings;
var force_merc = function(result) {
var new_merc = exports.canonical.spherical_mercator;
new_merc.input = result.input;
return new_merc;
};
exports.split_proj = function(literal) {
var parts = literal.split(' ');
// remove blank parts due to double spaces (common in proj epsg table)
var len = parts.length;
for (i = 0; i < len; i++) {
if (parts[i] === '') {
parts.splice(i, 1);
}
}
// break into key=value pairs, discarding +modifiers without values
var pairs = {};
parts.sort();
var new_len = parts.length;
for (i = 0; i < new_len; i++) {
var p = parts[i];
if (p.indexOf('=') != -1) {
var pair = p.split('=');
pairs[pair[0]] = pair[1];
}
}
return pairs;
};
var canonical_parts = exports.split_proj(exports.canonical.spherical_mercator.proj4);
var canonical_stringify = JSON.stringify(canonical_parts);
exports.parse = function(arg) {
if (arg instanceof Buffer) {
arg = arg.toString();
}
if (exists(arg)) {
var extension = path.extname(arg).toLowerCase();
var is_json = false;
if (extension == '.json' || extension == '.geojson') {
is_json = true;
}
var file_data = fs.readFileSync(arg);
if (!is_json) {
if (file_data[0] == '{') {
is_json = true;
} else {
var fstring = file_data.toString();
if (
((fstring.search('"type"') > -1) && (fstring.search('"coordinates"') > -1))
|| (fstring.search('"FeatureCollection"') > -1)
|| ((fstring.search('"geometryType"') > -1) && (fstring.search('"esriGeometry"') > -1))
)
{
is_json = true;
}
}
}
if (is_json) {
var file = JSON.parse(file_data);
if (file.crs && file.crs.properties && file.crs.properties.urn) {
arg = file.crs.properties.urn;
} else if (file.crs && file.crs.properties && file.crs.properties.name) {
arg = file.crs.properties.name;
} else {
arg = '+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs';
}
}
}
var result;
try {
result = srs._parse(arg);
} catch (e) {
if (arg.indexOf('ESRI::') !== 0) {
result = srs._parse('ESRI::' + arg);
} else {
throw e;
}
}
// detect mercator variants and
// replace with canonical.spherical_mercator
// TODO - early returns
if (result.name in oc(merc_names)) {
// this should be a fast track for many .prj files
return force_merc(result);
} else if (result.srid in oc(merc_srids)) {
return force_merc(result);
} else if (result.proj4 !== undefined && result.proj4.indexOf('+proj=merc') != -1) {
// catch case of gdal's translation to proj4 being used as input
if (result.proj4 === '+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +ellps=WGS84 +units=m +no_defs') {
return force_merc(result);
} else if (result.proj4 === '+proj=merc +lon_0=0 +lat_ts=0 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +units=m +no_defs') {
return force_merc(result);
}
// break into parts
// TODO - sort and remove less critical pairs
var parts = exports.split_proj(result.proj4);
if (JSON.stringify(parts) === canonical_stringify) {
return force_merc(result);
} /*else {
console.log(parts);
console.log(canonical_parts)
//if (parts.equals(canonical_parts)) {
//return force_merc(result);
}*/
}
return result;
};