[OSGeo-Standards] Re: WMS-C and handling of tiled=true? Indicating a Restriction or an Ability

[Satoru Takagi]

Hi Jody,

First of all, I had acted in the world different from the GIS culture 
that centered on OGC. If anything, I belong to the world of SVG and 
Semantic Web of W3C. Moreover, I am in Japan. Therefore, I might have a 
sense different from people of the GIS community. And, I am continuing 
the design of the Web Mapping Platform architecture based on SVG.

The map tiling can be achieved by interpreting like the following static 
data.

<tiledmap>
  <tile bbox="0,0,10,7"    xlink:href="0_0.jpg"/>
  <tile bbox="10,0,20,7"   xlink:href="1_0.jpg"/>
  <tile bbox="20,0,20,7"   xlink:href="2_0.jpg"/>
  <tile bbox="0,7,10,14"   xlink:href="0_1.jpg"/>
  <tile bbox="10,7,20,14"  xlink:href="1_1.jpg"/>
  <tile bbox="20,7,30,14"  xlink:href="2_1.jpg"/>
  <tile bbox="0,14,10,21"  xlink:href="0_2.jpg"/>
  <tile bbox="10,14,20,21" xlink:href="1_2.jpg"/>
  <tile bbox="20,14,30,21" xlink:href="2_2.jpg"/>
</tiledmap>


Because the position of each tile is shown by bbox property, the tile 
instance to which this document refers can have any URL. Even of course 
static URL.

On the other hand, data from WMS also can be referred to as a tile. 
Because protocol for WMS can be described by URL though it has special 
query part.

Example:
<tiledmap>
  <tile bbox="0,0,10,7" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=0,0,10,7"/>
  <tile bbox="10,0,20,7" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=10,0,20,7"/>
  <tile bbox="20,0,20,7" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=20,0,20,7"/>
  <tile bbox="0,7,10,14" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=0,7,10,14"/>
  <tile bbox="10,7,20,14" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=10,7,20,14"/>
  <tile bbox="20,7,30,14" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=20,7,30,14"/>
  <tile bbox="0,14,10,21" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=0,14,10,21"/>
  <tile bbox="10,14,20,21" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=10,14,20,21"/>
  <tile bbox="20,14,30,21" 
xlink:href="http://....?REQUEST=GetMap&FORMAT=image/png&....&BBOX=20,14,30,21"/>
</tiledmap>

That is, it is possible to provide for the mechanism of such tiling 
independently of WMS. Of course, they unites loosely with WMS by 
primitive URL.

On the other hand, the link to each tile is expanded with inline in this 
tiling method. Therefore, there might be a case where it becomes a 
problem on the efficiency side. On the other hand, the access method of 
each tile data is free as long as it is expressible by URL. It might be 
a freer specification from the specification that restricts query part 
of URL.

I think that this is on the extension of a past discussion concerning 
the difference of the architecture between REST and SOAP(RPC).


And we implemented this architecture based on SVG specifications. 
Because there was a function to import and arrange external contents in 
SVG specification (that is <image> element) , it was not necessary to 
expand the original element and property for tiling. As a result, in Web 
Map Platform by SVG, it was able to prescribe most of the specifications 
for tiling without new expansion.

There are the specifications and the sample in the following URL.
  SVG Map data divided into mosaic tegular :
    http://blog.svg-map.com/2008/07/format-and-proc.html
  Relationship between WMS and SVG Map:
    http://blog.svg-map.com/2008/07/relationship-be.html

See Also :
  Supplementation: SVG Map data divided into mosaic tegular:
    http://blog.svg-map.com/2008/07/supplementation.html
  Relationship between WMS and SVG Map:
    http://blog.svg-map.com/2008/07/relationship-be.html
  Example of tiled map:
    http://blog.svg-map.com/2008/08/base-map-of-jap.html
    http://blog.svg-map.com/2008/08/the-system-whic.html
  Architectures of Tiled Map Services:
    http://blog.svg-map.com/2008/07/architectures-o.html

Regards,

Satoru Takagi

Jody Garnett さんは書きました:
> Hi Satoru;
> 
> Now that I am at work I realized I answered your comment incorrectly. 
> The TileServer your describe is good; I will just need a way to tell (as 
> a client) that such a server is not a general purpose WMS (and thus uDig 
> will be forced to only make GetMap requests in accordance with the 
> VendorSpecificParameter restrictions.
> 
> Perhaps this is the intentions of the "tiled=true" 
> VendorSpecificParameter for GetMap?
> - My impression was that tilted=true was intended to let a full fledged 
> WMS implementation switch GetMap between dispatching to the normal 
> rendering path vs dispatching to tile lookup?
> - If tiled=true is indeed a flag indicating that *only* tile lookup is 
> supported the my workflow will need to be modified. Something like 
> checking the GetMap preamble documented by the VendorSpecificParameters; 
> and iff "tiled=true" was present, I could assume that a generic GetMap 
> was not supported ...
> 
> Hopefully this is the correct venue for these discussions.
> Jody
> 
> Satoru Takagi wrote:
>> Hi all,
>>
>> There seems to be the considerable difference between the function 
>> that is necessary for a tiling server and the function of the WMS server.
>>
>> The simplest tiling server can be achieved even by the simple file 
>> system (For example, mere httpd without CGI, servlet, PHP..) which 
>> stored tile files and metadata.
>>
>> Therefore, I think that the spacifications for tiling server should be 
>> designed based on simpler mechanism (the basic URL based web) rather 
>> expansion of the functions and its specifications of a dynamic server 
>> such as WMS.
>>
>> Regards,
>>
>> Satoru Takagi
> 
> 

-- 
--
高木　悟（Satoru Takagi)
ＫＤＤＩ株式会社 コア技術統括本部 ネットワーク技術本部
技術戦略部 企画調査Ｇ
Email:sa-takagi at kddi.com

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