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

[Andreas Hocevar]

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

OpenLayers uses the original Google API, v2.x. Using 
OpenLayers.Layer.Google is nothing else than using a GMaps Map directly, 
you just access it wrapped by an OpenLayers layer type, not by the API 
directly.

I also do not see a violation of the terms of use. We even make sure 
that the Terms of Use link is clickable if we render other layers on top 
of Google.

There is, however, a known issue: if you create your map at a smaller 
size and switch from one Google Layer type to another after resizing it 
to your big map, tiles will only be loaded for the area of the old 
extent. There is a patch that appears to solve this issue. You can try 
it: http://trac.openlayers.org/ticket/1797

Regards,
Andreas.

> 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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>> Users at openlayers.org
>> http://openlayers.org/mailman/listinfo/users
>>
>>   
>>     
>
>
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-- 
Andreas Hocevar
OpenGeo - http://opengeo.org/
Expert service straight from the developers.