[Mapserver-users] Oracle Spatial Extents

[Vladimir Guzmán]

Hi, Frans.

It takes 29 secs to get the full extents of the geometry, which has 
~2500 elements.
The oracle gets all the ~2500 extents, and then gets the minimum and 
maximum value for X and Y, so I obtain the full extents this way.
I'm using Oracle Spatial 9i.
My data is not geodetic (SRID=1=>Sinusoidal WGS84)
I don't understand very well the difference between geodetic and 
non-geodetic data, anyway, at the beginning I had my data in SRID=8307 
and I wasn't able to use the MBR functions, so I switched to SRID=1.

And trying the Fernando Simon's suggestion 
(http://mapserver.gis.umn.edu/data2/wilma/mapserver-users/0407/msg00767.html), 
I had no luck.
The level with SDO_TUNE.ESTIMATE_TILING_LEVEL was 6, but the query 
didn't get better.  Besides, after indexing this way I wasn't able to 
draw the geometry outside the extents.

My question now is: Is there another way to get the extents of a geometry?
I also tried SDO_AGGR_MBR with the same results (too much time executing 
the query).

The point is that I use a lot this functionality in Postgis 
(extent(the_geom)) with very large datasets and Postgis does it very fast.

Any help will be very appreciated.

Thanks a lot in advance,


-- 
Vladimir Ilich Guzmán R.
------------------------
http://maintask.com 



Frans Knibbe wrote:

> Vladimir,
>
> Does it take 29 seconds for all ~2500 extents? What version of Oracle 
> Spatial are you using? The function you are using is not supported for 
> geodetic data in Oracle 9 but it is in Oracle 10.  The Oracle metalink 
> article 241661.1 explains why the MBR functions were not supported in 
> version 9. Are you sure you want to use the MBRs?
>
> I don't know if the MBR functions use the R-tree index (which stores 
> MBRs), but I can imagine the algorithm for calculating a MBR is more 
> complex for geodetic data than for projected data, which might explain 
> the long duration. Maybe you could make a copy of your table and 
> project it, then see how long it takes to execute the same query.
>
> Greetings,
>
> Frans**
>
> Vladimir Guzmán wrote:
>
>> Hello.
>> I need to get the extents of a geometry in Oracle Spatial.
>> I'm using the following query:
>>
>> MIN(SDO_GEOM.SDO_MIN_MBR_ORDINATE(GEOMETRY_TABLE.ORA_GEOMETRY, 
>> m.diminfo,1)) as XMIN,
>> MIN(SDO_GEOM.SDO_MIN_MBR_ORDINATE(GEOMETRY_TABLE.ORA_GEOMETRY, 
>> m.diminfo,2)) as YMIN,
>> MAX(SDO_GEOM.SDO_MAX_MBR_ORDINATE(GEOMETRY_TABLE.ORA_GEOMETRY, 
>> m.diminfo,1)) as XMAX,
>> MAX(SDO_GEOM.SDO_MAX_MBR_ORDINATE(GEOMETRY_TABLE.ORA_GEOMETRY, 
>> m.diminfo,2)) as YMAX
>> FROM GEOMETRY_TABLE, user_sdo_geom_metadata m
>> WHERE m.table_name = 'GEOMETRY_TABLE' AND m.column_name = 
>> 'ORA_GEOMETRY';
>>
>> But Oracle takes 29 seconds (!) to get the extents.
>> Is this a normal behavior?
>> The geometry is indexed using:
>>
>> CREATE INDEX GEOMETRY_TABLE_SPATIAL_IDX
>> ON GEOMETRY_TABLE(ORA_GEOMETRY)
>> INDEXTYPE IS MDSYS.SPATIAL_INDEX;
>>
>> The geometry has ~2500 records.
>> The geometry's SRID is 1 (Sinusoidal WGS84).
>> Am I using the wrong query?
>> Is there another way?
>>
>> Anyone has experienced a related problem?
>>
>> Thanks in advance for your help.
>>
>
>
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