Hello Noel,
I think you can find more information on the computation of the upper hull
values in [FFS00] "Implementing Geospatial Operations in an Object-Relational
Database System".
For testing, we used oracle, where we had transient tables.
I am not sure whether we have transient memory tables in SQLite. If yes, you
can use them.
The simple box elimination always goes along with a full table scan. Assume you
have the polygons of complete Europe in your database and you do a selective
spatial query, you still have to evaluate all bounding boxes of all polygons.
In that case a hierarchical organization of the data, e.g. by the Relational
Quadtree or the Relational R-tree, is certainly much more efficient. If you
always select let's say more than 10% of all polygons, then the box filtering
might be enough.
Best Martin
----- Ursprüngliche Mail ----
Von: Noel Frankinet <[EMAIL PROTECTED]>
An: sqlite-users@sqlite.org
Gesendet: Freitag, den 19. Mai 2006, 09:38:13 Uhr
Betreff: Re: AW: [sqlite] Re: spatial sqlite anyone ?
Martin Pfeifle wrote:
>Hi,
>I think the simplest solution would be to put a spatial index on top of the
>B-tree, that's what e.g. Oracle does in their Spatial Cartridge.
>Basically you store the index data in relations and index these relations by
>B-trees.
>In this case, you do not have to change the core code of SQLite. You can
>already do this now.
>Nevertheless, it would be nice, if SQlite supports somehow the "extensible
>indexing interface".
>So, you ask a spatial query and in the background the system uses the index
>data stored in relations.
>We have done a lot of research on that topic. To get acquainted to the basic
>idea, you might have a look at
>"The Paradigm of Relational Indexing: A Survey".
>
>In my opinion, a direct integration of a spatial index is of course
>preferable, but who is going to do that?
>
>Best Martin
>
>
>
Hello Martin, hello All,
Thank you for the above link, it is very useful.
I definitely want to go the spatial index map to btree index way.
I especially like the quad-tree select because I understand it and I
already have most of the building blocks :
SELECT DISTINCT idx.id
FROM polygons_quadtree idx,
TABLE(ZDecompose(BOX()) titles,
Table(ZupperHull(tiles.zval)) uh
WHERE (idx.zval BETWEEN tiles.zval AND ZHi(tiles.zval))
OR (idx.zval = uh.zval);
Well almost, I know how to make ZDecompose, I still not sure about ZHi,
ZUpperHul, do you have any more pointers ?
I didn't konw the TABLE statement to return a pseudo table,
unfortunately, it seems not available in sqlite, can it be emulated by a
transient memory table ?
Do you think that such a complex statement has any chance to be speedier
than a simple bbox elimination ?
Thanks again,
Best regards
--
Noël Frankinet
Gistek Software SA
http://www.gistek.net
