[gdal-dev] WMS Issues Two Requests

[Even Rouault]

Le vendredi 07 février 2014 15:08:07, Martin Lewis a écrit :
> Thanks Jukka.
> 
> I have been having a play around and the 'width' and 'height' sent in the
> WMS Request string appears to be BlockSizeX and BlockSizeY and I think I
> understand now.
> 
> Removing the BlockSizeX and Y  from the XML meant that block size was
> defaulted to 1024 and 1024 - again resulting in two requests.
> 
> Setting BlockSize to 256 and 256 and you get loads of requests as expected
> to fulfil the whole request of 1076 * 787
> 
> However setting the BlockSizeX and Y to the same as SizeX and SizeY (1076,
> 787) in the DataWindow section, created a WMS Request that had 'height' and
> 'width' set to 787 and 1076 - which appears to be exactly what is required.
> 
> This cut the time from start of request to drawing on the screen by 5 times
> - from 5 secs to 1 sec, exactly what I was after.
> 
> I suppose some WMS servers may not support the BlockSize that is being
> requested. (when I set the BlockSize to 2048, one map server was returning
> an error saying it was above the allowed 2001 width!!?)

That's what Jukka mentionned in his first email. Most servers have a maximum 
width/height to avoid being brought down by evil clients. So you need to use 
more reasonable block sizes, and yes you'll request a few more pixels than 
needed, but that's life...

> 
> However at the current moment what is requested appears to be within limits
> of all the servers we talk to.
> 
> Is it as simple as this or is there anything that I have missed?
> 
> Once again thanks for your help.
> 
> Martin
> 
> 
> 
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