[OpenLayers-Dev] [OpenLayers-Users] Advice about Google layer limitations

[Adrian Popa]

I asked the same question on Google API forums, and it looks like the 
original Google API doesn't have this limitation.

I did some tests and you can see the results on this thread: 
http://groups.google.com/group/google-maps-api/browse_thread/thread/97d62ed9a85e665e

I would like to know if there is something that can be done from the 
OpenLayers side, or is this a known limitation. Is OpenLayers scraping 
images from Google, or is it using the API just like any other Google 
Maps client?

Thank you,
Adrian

Adrian Popa wrote:
> Hello everybody,
>
> I would  like to share with you my findings about the usage of Google 
> background on very large maps. I have to render a map with the screen 
> resolution of about 4500x3100 (on a wall of screens). It works ok with 
> WFS layers, OSM and even Microsoft Virtual Earth, but I have issues with 
> Google and Yahoo.
>
> When I switch to the google layer, the background turns gray and then 
> the browser starts loading the images. After about 130s of loading 
> (there are quite a lot of pictures), I notice that google starts 
> throwing back HTTP 403 errors (Resource temporary unavailable). Just 
> before seeing these errors, some images (the center part of the map) 
> start appearing, but only about 1/4 of the map is drawn. If I wait about 
> 5 minutes, the download process gives up (it still receives HTTP 403 
> errors all this time), but it displays the rest of the images - which 
> were apparently downloaded before the 403 error appeard.
>
> I'm thinking it manages to download most of the visible images + some 
> images in the bbox (which is quite large), but not all the images before 
> getting errors. The problem is the Google API doesn't display what it 
> downloaded, but waits for more images to be downloaded.
>
> After analysing the data, I noticed that when the first DNS query is 
> done for the Google cache, it receives back 4 IP addresses. However, 
> only the first 2 IPs are used for traffic - and these 2 IPs start 
> sending back HTTP 403 errors after a while.
>
> I would like to know if the following are possible:
> 1. configure the Google API to use all the IP addresses it receives in 
> the DNS query - maybe this avoids the 403 erros
> 2. configure the Google API to display the pictures received without 
> waiting for more pictures to download. I'm not sure if this is possible 
> - maybe the images are pipelined through the same connection - and they 
> are shown only when the connection closes.
> 3. reduce the bbox for the Google Layer - this should be fine for my 
> needs - and maybe avoids the 403 errors.
>
> With regard to the Yahoo layer - things are better. It loads faster for 
> the same size (they don't seem to have a "throttling" mechanism), but it 
> only displays the final image when all the bits are downloaded - so it's 
> as fast as the slowest image. Can this behavoir be changed from within 
> OpenLayers?
>
> Thanks,
> Adrian
>
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