Hi,
I am in the process of creating a feature based on an Oracle Table that
is properly indexed and has an entry in USER_SDO_GEOM_METADATA.
Clicking the Generate button to get the extents returned incorrect
values.
I checked the MBR with the following code and got the same values as
OracleNG...
select sdo_aggr_mbr(geom_location)
from <tablename>
141.8076171875, -16.8662109375, 148.2353515625, -15.568359375
Obviously OracleNG is using SDO_AGGR_MBR as there's no way else to get
the strange results, which
aren't so strange when you read the Oracle docs - "...by contrast, the
SDO_AGGR_MBR function can operate on
subsets of rows."
I then checked using the following statement and got the correct values
SELECT SDO_TUNE.EXTENT_OF('TABLENAME', 'GEOM_LOCATION')
FROM DUAL;
137.6845703125, -29.197265625, 152.1845703125, -10.810546875
However, SDO_TUNE.EXTENT_OF only works with 2 dimensional geometries.
Now even though we are only working with 2 dims here, if someone is
using
an LRS dim or Z, it won't work.
This provides a reasonable approximation without much of a performance
hit ...
SELECT SDO_AGGR_MBR(ch)
from (select SDO_AGGR_CONVEXHULL(SDOAGGRTYPE(geom_location, 0.001)) ch
FROM <tablename>);
... but you would have to look up the tolerance from
USER_SDO_GEOM_METADATA.
The best solution is just to get the diminfo from
USER_SDO_GEOM_METADATA. The current
way of generating the data is flawed in any case for all databases, not
just Oracle. I
know I have put in the diminfo for my entire area of concern even though
it will be
two years before the data is fully populated. I would suspect most
people would put in
the layer size in the diminfo up front and that the data may not reflect
the actual bounds
required.
On the other hand, if we are not going to fix this, then there needs to
be a clear warning about
generated extents possibly (probably) being inaccurate if adding an
Oracle feature, right next to
the 'Generate' button.
Cheers
Stuart
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