When Google went insane and decided to charge excessive amounts for use of their mapping APIs I looked for an alternative. One of the features I needed was support for KML, since my website uses it quite extensively. Which led me to Here Maps.
After a fair amount of work, I managed to convert most of my pages to use Here Maps, but there’s still a few stuck using Google Maps due to features that are unique to Google Maps. This was OK, since my usage was now mostly under the $200 per month of free credit. But recently one of my Google Maps pages started to get a lot of hits due to a new inbound link and I zoomed past $200 free credit into eye-wateringly expensive territory. So time to convert that page to Here Maps.
Converting maps that load KML from Google Maps to Here Maps is generally straightforward, just learn a different API and redo the JavaScript on your page. But the architecture of KML support on the two platforms is different. Google loads the KML on their servers, generates map tiles and uses those to display the KML file. Here Maps loads the KML file in the browser and add markers, polylines etc to the map directly.
The Google approach has one major advantage, it copes well with large KML files. Since the move to Here Maps, I’ve had to stop loading up KML files that I know have more than a few thousand markers in them. Google’s KML support also means you can load up KML files from external sources, whereas Here Maps will generally fail with external KML (unless CORS has been configured to support it on the other server).
Google KML has a few disadvantages. If the KML changes regularly then you’ll probably suffer from caching issues, since the old map tiles can keep getting returned for some time after the KML changes. Also the rendering isn’t as good as Here Maps, since the KML is rendered as an image at each zoom level rather than as live objects on the map
The thing that had stopped me moving this page over to Here Maps was the inability to display remote KML data. Then it struck me that the fix for that was fairly straightforward. Add a local piece of server code that loads up the KML file from the remote source and returns it to the browser so it’s treated as a local URL. That was easy enough to code up. Then I just needed to cope with a few edge cases, Google Maps copes with KMZ files, but Here Maps doesn’t. And some servers didn’t like requests coming from something that wasn’t a browser. So I eventually came up with this
public void ProcessRequest(HttpContext context) {
context.Response.ContentType = "application/vnd.google-earth.kml+xml";
var url = context.Request.QueryString["url"];
var httpRequest = (HttpWebRequest) WebRequest.Create(url);
httpRequest.Method = "GET";
// pretend to be a browser
httpRequest.UserAgent =
"Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36";
using(var httpResponse = (HttpWebResponse) httpRequest.GetResponse()) {
var responseStream = httpResponse.GetResponseStream();
if (responseStream != null) {
var archiveStream = new MemoryStream();
responseStream.CopyTo(archiveStream);
archiveStream.Position = 0;
// see if it's a zip file
try {
var archive = new ZipArchive(archiveStream);
using(var stream = archive.Entries[0].Open())
using(var archiveReader = new StreamReader(stream)) {
context.Response.Write(archiveReader.ReadToEnd());
}
} catch (Exception) {
archiveStream.Position = 0;
var reader = new StreamReader(archiveStream);
var response = reader.ReadToEnd();
context.Response.Write(response);
reader.Close();
}
// Close both streams.
responseStream.Close();
}
}
}
