Using Google Ditu maps with Satellite imagery for China
Erik Wilde was pointing out the disparities between Google Maps and Google Ditu, or their Chinese version of maps. However, Google Ditu doesn’t have satellite imagery.
There are several easy ways to fix this. The first was to look at the Ditu tiles, and confirm they are the same as Google’s nominal tiling scheme. Which means you can add the China Street tiles as a simple GTileLayerOverlay with Google Maps standard satellite view underneath. This was incredibly easy with Mapstraction and I put up a demo here.
For bonus points I even added a Mapufacture syndicated feed of Erik’s venues for LocWeb2008 and nearby Wikipedia articles from Geonames.
The other way
The terms of how mixing Google’s various tiles together isn’t clear. So the other way to address his issue is to use the freely available data.
Namely, OpenStreetMap for roads, OpenAerialMap or other remote imagery, and run in OpenLayers. Here is the same map done with open data and open source. The resolution or completeness isn’t there yet, but you can see where it’s going and the ability to be use the information as you want is very appealing.
My name is
January 29th, 2008 at 5:00 pm (#)
Hi!
Sorry to barge in on you like this, but I’ve been poking around mapstraction for a while, and there are a bunch of questions I just can’t seem to find an answer to. Anyway, I’ve even tried to find the mailing list but to no avail. The one referenced on http://mapstraction.com/trac does not exist. So, if you could be so kind to nudge me in the right direction, that would be great!
Thank you for your time!
Kind regards, Vanja
January 29th, 2008 at 11:53 pm (#)
Hi Vanja – sorry about the confusion. I updated the front page of Mapstraction.com, but not the rest of the trac and wiki.
The mailing list has moved to:
http://lists.mapstraction.com/listinfo.cgi/mapstraction-mapstraction.com
Definitely send any/all your questions to the list and we’ll help you out.
June 23rd, 2008 at 7:08 am (#)
Hi,
I noticed in your Beijing example that the streets in the ditu maps don’t line up properly with the streets in the satellite imagery. Is there some way to apply an offset, so that they line up better?
thanks!
June 23rd, 2008 at 8:58 am (#)
@karl – the problem is that the tilesets are in different coordinate reference systems. This is the method of converting the spherical latitude & longitude to a flat image.
Google Ditu uses B-54 (Guass-Krueger), while Google Maps is a Spherical Mercator, or “Web Mercator” known as EPSG:3785
So what has to happen is a warping would occur to get the two images to overlay properly.