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I want to draw a city district area on Google Maps using Polygon class and an array of lat/lng coordinates.
OpenStreetMap provides me all data I need — if I type some district name I can get useful data in OSM XML format, for example OSM drawn polygon of “Vecmilgravis” district in Riga, Latvia and it's data in OSM XML format.
The problem is all those node nodes are sorted in some weird order, so if I just extract all lat and lng pairs and make an coordinates array for Google Maps Polygon class I see not what I've expected:
Markers are displayed correctly 'cos coordinates order is not important for them, but polygon is messed up 'cos of wrong coordinates order I copypasted from OSM data.
So, how do I extract (or sort manually) OSM nodes coordinates in right order?
462
To make a path or polygon into a 3D object, click Altitude. A "New Path" or "New Polygon" dialog will pop up. You may need to move it out of the way before moving on to the next step. To draw the line or shape you want, click a start point on the map and drag.
Google Maps uses OSM for data. POGO uses Google Maps. This is the coorelation : r/TheSilphRoad.
OSM gives better performance in various urban centres as compared to Google Maps. Google Maps are the best for online purposes. OpenStreetMap allows the users to download the maps that can be used offline also for either finding a route or identifying a location.
With OSM, map data for the whole planet can be downloaded and used completely offline. Google Maps can only cache small region and generally can not work without an Internet connection. OSM dataset can be used to large-scale geocoding, routing and analysis, which would be impossible using Google Maps.
This is probably the "right" way to do it:
(there might be a more efficient way to do it)
code snippet:
var geocoder;
var map;
var centerPt;
var markers = [];
function initialize() {
var map = new google.maps.Map(
document.getElementById("map_canvas"), {
center: new google.maps.LatLng(37.4419, -122.1419),
zoom: 13,
mapTypeId: google.maps.MapTypeId.ROADMAP
});
var path = [];
var xmldata = xmlParse(xmlBoundaryData);
var nodes = xmldata.getElementsByTagName("node");
var bounds = new google.maps.LatLngBounds();
var nodeArray = [];
// get the coordinate data out of the "nodes"
for (var i = 0; i < nodes.length; i++) {
var pt = new google.maps.LatLng(nodes[i].getAttribute("lat"),
nodes[i].getAttribute("lon"));
path.push(pt);
nodeArray[nodes[i].getAttribute("id")] = pt;
var marker = new google.maps.Marker({
position: pt,
map: map,
title: "" + i
})
markers.push(marker);
bounds.extend(pt)
}
var waysArray = [];
// get the ways, putting the "nodes" in "way" order
var ways = xmldata.getElementsByTagName("way");
for (var j = 0; j < ways.length; j++) {
var waypath = [];
var nd = ways[j].getElementsByTagName("nd");
for (var i = 0; i < nd.length; i++) {
waypath.push(nodeArray[nd[i].getAttribute("ref")]);
}
waysArray.push(waypath);
var waypoly = new google.maps.Polyline({
path: waypath,
map: map,
strokeColor: "#0000FF"
})
}
// assemble the "ways" into a polygon by concatenating together at the common points
console.log("number of ways="+waysArray.length);
var polypath = [];
for (var i = 0; i < waysArray.length; i++) {
if (i == 0) {
// first "way"
console.log("way 0, ends at " + waysArray[i][0].toUrlValue(6));
for (var j = 0; j < waysArray[i].length; j++) {
polypath.push(waysArray[i][j]);
}
} else if (polypath[polypath.length - 1].equals(waysArray[i][0])) {
console.log("way " + i + ", ends at " + waysArray[i][0].toUrlValue(6));
for (var j = 1; j < waysArray[i].length; j++) {
polypath.push(waysArray[i][j]);
}
} else if (polypath[polypath.length - 1].equals(waysArray[i][waysArray[i].length - 1])) {
console.log("way " + i + " (rev), ends at " + waysArray[i][waysArray[i].length - 1].toUrlValue(6));
for (var j = waysArray[i].length - 2; j >= 0; j--) {
polypath.push(waysArray[i][j]);
}
} else {
// not adjacent to the end, try again later (push it on to the end of the array)
waysArray.push(waysArray[i]);
}
}
var polygon = new google.maps.Polygon({
map: map,
path: polypath
});
map.fitBounds(bounds);
}
google.maps.event.addDomListener(window, "load", initialize);
function xmlParse(str) {
if (typeof ActiveXObject != 'undefined' && typeof GetObject != 'undefined') {
var doc = new ActiveXObject('Microsoft.XMLDOM');
doc.loadXML(str);
return doc;
}
if (typeof DOMParser != 'undefined') {
return (new DOMParser()).parseFromString(str, 'text/xml');
}
return createElement('div', null);
}
var xmlBoundaryData = '<?xml version="1.0" encoding="UTF-8"?><osm version="0.6" generator="CGImap 0.4.0 (20233 thorn-01.openstreetmap.org)" copyright="OpenStreetMap and contributors" attribution="http://www.openstreetmap.org/copyright" license="http://opendatacommons.org/licenses/odbl/1-0/"><node id="939092112" visible="true" version="3" changeset="9125708" timestamp="2011-08-25T22:47:10Z" user="Raitisx" uid="105318" lat="57.0408668" lon="24.0680754"><tag k="source" v="Rīgas pilsētas teritorijas plānojums"/></node><node id="956004391" visible="true" version="5" changeset="36231114" timestamp="2015-12-28T22:52:59Z" user="AkageMuk" uid="2012081" lat="57.0299437" lon="24.1089277"><tag k="name" v="Vecmīlgrāvis"/><tag k="name:de" v="Alt-Mühlgraben"/><tag k="name:lv" v="Vecmīlgrāvis"/><tag k="name:ru" v="Вецмилгравис"/><tag k="place" v="suburb"/><tag k="wikipedia" v="lv:Vecmīlgrāvis"/><tag k="wikipedia:ru" v="Вецмилгравис"/></node><node id="1412648728" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:50Z" user="Raitisx" uid="105318" lat="57.0237064" lon="24.1172858"/><node id="1412648732" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:50Z" user="Raitisx" uid="105318" lat="57.0237837" lon="24.1146783"/><node id="1412648733" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0239283" lon="24.1201001"/><node id="1412648734" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0239694" lon="24.1120189"/><node id="1412648735" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0244130" lon="24.1218642"/><node id="1412648741" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0252736" lon="24.1235470"/><node id="1412648742" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0252901" lon="24.1068387"/><node id="1412648745" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0259421" lon="24.0865922"/><node id="1412648749" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0267091" lon="24.1003177"/><node id="1412648750" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0272530" lon="24.0901290"/><node id="1412648753" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0272650" lon="24.1261230"/><node id="1412648754" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0277863" lon="24.0940634"/><node id="1412648755" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0277928" lon="24.0850352"/><node id="1412648760" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:51Z" user="Raitisx" uid="105318" lat="57.0298488" lon="24.1289978"/><node id="1412648766" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0322322" lon="24.0795026"/><node id="1412648767" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0324695" lon="24.1317941"/><node id="1412648768" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0336179" lon="24.1289290"/><node id="1412648769" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0342914" lon="24.1256628"/><node id="1412648770" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0346037" lon="24.1223190"/><node id="1412648771" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0348498" lon="24.1188739"/><node id="1412648772" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0348667" lon="24.0758427"/><node id="1412648775" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0353858" lon="24.1167861"/><node id="1412648783" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0377249" lon="24.1087940"/><node id="1412648786" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:52Z" user="Raitisx" uid="105318" lat="57.0382325" lon="24.0717365"/><node id="1412648787" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:53Z" user="Raitisx" uid="105318" lat="57.0383366" lon="24.1072823"/><node id="1412648788" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:53Z" user="Raitisx" uid="105318" lat="57.0398108" lon="24.1061825"/><node id="1412648789" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:53Z" user="Raitisx" uid="105318" lat="57.0403684" lon="24.1061945"/><node id="1412648792" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:53Z" user="Raitisx" uid="105318" lat="57.0418628" lon="24.1028049"/><node id="1412648793" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:53Z" user="Raitisx" uid="105318" lat="57.0425852" lon="24.0987029"/><node id="1412648798" visible="true" version="1" changeset="9125708" timestamp="2011-08-25T22:45:53Z" user="Raitisx" uid="105318" lat="57.0430687" lon="24.0645903"/><node id="1412648799" visible="true" version="1" 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v="administrative"/><tag k="source" v="Rīgas pilsētas teritorijas plānojums"/></way><way id="127683719" visible="true" version="3" changeset="13788614" timestamp="2012-11-07T18:35:30Z" user="briedisUNrepshe" uid="780955"><nd ref="1412648789"/><nd ref="1412648788"/><nd ref="1412648787"/><nd ref="2001673384"/><nd ref="1412648783"/><nd ref="1412648777"/><nd ref="1412648775"/><nd ref="1412648771"/><nd ref="1412648770"/><nd ref="1412648769"/><nd ref="1412648768"/><nd ref="1412648767"/><tag k="admin_level" v="10"/><tag k="boundary" v="administrative"/><tag k="source" v="Rīgas pilsētas teritorijas plānojums"/></way><way id="127683787" visible="true" version="2" changeset="9316551" timestamp="2011-09-16T14:24:16Z" user="Raitisx" uid="105318"><nd ref="1412648809"/><nd ref="1412648814"/><nd ref="1412648822"/><nd ref="1412648830"/><nd ref="1412648829"/><nd ref="1412648821"/><nd ref="1412648815"/><nd ref="1412648819"/><nd ref="1412648828"/><tag k="admin_level" v="10"/><tag k="boundary" 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ref="127683755" role="outer"/><member type="way" ref="127683719" role="outer"/><member type="way" ref="127683753" role="outer"/><member type="way" ref="127683754" role="outer"/><member type="way" ref="127683772" role="outer"/><member type="way" ref="80500002" role="outer"/><member type="way" ref="80499981" role="outer"/><member type="way" ref="127683787" role="outer"/><member type="node" ref="956004391" role="admin_centre"/><tag k="admin_level" v="10"/><tag k="boundary" v="administrative"/><tag k="name" v="Vecmīlgrāvis"/><tag k="name:de" v="Alt-Mühlgraben"/><tag k="name:lv" v="Vecmīlgrāvis"/><tag k="name:ru" v="Вецмилгравис"/><tag k="type" v="boundary"/></relation></osm>';html,
body,
#map_canvas {
height: 100%;
width: 100%;
margin: 0px;
padding: 0px
}<script src="https://maps.googleapis.com/maps/api/js?libraries=geometry&key=AIzaSyCkUOdZ5y7hMm0yrcCQoCvLwzdM6M8s5qk"></script>
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