[postgis-users] Points or boundaries more efficient for querying?

[Guido Lemoine]

Nick,

Both GE and VE are mixes of low res and high res tile sets, but using
the same coding scheme for both. This allows direct access to the (relevant)
tile sets at any level, which, together with caching and pre-emptive loading
and server load balancing, leads to their speed.

The only "scientific" objection you may have is that you need to stick 
to the
tile system's fixed projection and pixels spacing (determined by the
"level"). But I reckon that in your case (mixing global low with local
high res), you would want to stick to 1 projection anyway.

Since tile coding is implicit, the viewing client can calculate the required
tile codes, given a [geographical] view window (a ROI). No need to do any
spatial querying. The servers do not need to do resampling or painting (as
in WMS), they just send the requested tiles. The magic is in the simplicity.

GL

Nick Bower wrote:

>>If tile boundaries are implicit (i.e. fixed by your choice of tiling grid
>>and spacing), there is no need to store and or query tile outlines at
>>all.
>>Have a look at how WorldWind, Google and Virtual Earth do this. VE
>>is actually VERY cool at this (cooler than GE!). They even provide the
>>code.
>>    
>>
>
>Ok it will be interesting to see if these handles low res grids
>accompanied by overlapping high res ones over select ROIs.  It would
>seem like you are suggesting them not to use PostGIS at all here.
>
>  
>
>>I came across some OSgeo specs on this as well
>> (http://wiki.osgeo.org/index.php/Tile_Map_Service_Specification)
>>Thinking about implementing this sometime soon.
>>    
>>
>
>This seems like a query API - a cartographic OpeNDAP.  I was more
>enquiring about the search implementation, not the API used to access
>it.
>
>Thanks!  Nick.
>  
>

-- 

----------------------------------------------------------------
Joint Research Centre, European Commission
Institute for the Protection and Security of the Citizen (IPSC)
Unit: Support to External Security
Via E. Fermi, 1 TP 267 Ispra 21020 (VA), Italy
Tel. +39 0332 786239 (direct line) Fax. +39 0332 785154
WWW: http://ses.jrc.it
----------------------------------------------------------------
Disclaimer:
Views expressed are those of the individual and do not represent the
views of the European Commission