[Gvsig_english] Question on GeoBD and Metadata when exporting toOracle

Thu Sep 24 11:16:03 CEST 2009

Hello, Wolfgang.

When you export a vector layer to Oracle Spatlai/Locator, the sequence of actions is as follows:

- if a table with the same name exists, it's deleted (dropped in cascade mode). This also removes spatial indices associated with the table
- the new table is created
- geometry metadata for this table name is removed (if existed)
- new geometry metadata is written in USER_SDO_GEOM_METADATA
- a spatial index on the geometry column is created
- table records are added (no commits here)
- a single final commit is performed

The tolerance parameter in the metadata is always set to 0.5. Dimension names are set to 'X', 'Y' and 'Z' (if needed) or 'LONGITUDE' and 'LATITUDE'. Max. and min. values for X and Y are set according to the layer's bounding box. Min. and max. values for 'Z' (if needed) are always set to 0 and 100 (this is not very nice, but has no bad effect since the Z value does not currently take part in any geometric operation). Dimension names can be anything you want. You could use 'BREITE' instead of 'LATITUDE', 'EASTING' instead of 'X' or whatever.

SDO_TOLERANCE_1 and  SDO_TOLERANCE_2 refer to tolerance for X and Y perhaps?

Remember that the tolerance unit is implicit and depends on the table's coordinate system (SRID). If the SRID corresponds to a geodetic coordinate system (latitude, longitude), then the tolerance is assumed to be expressed in meters. If the SRID corresponds to a projected coordinate system (such as the German EPSG:3146X series) then the tolerance is assumed to be expressed in the same unit used by the coordinate system (usually meters). This also applies if the SRID is NULL. According to this, it would be a bad idea to have a table with geometries whose vertices are in latitude and longitude and setting the SRID to NULL, because the tolerance (0.5) would correspond to a few dozens of kilometers.

The tolerance settings are very unlikely to have any effect when you work with gvSIG because the application checks again the true relationship between geometries after they have been converted to the gvSIG geometry model. In other words: the 'select by rectangle' tool should not behave in a strange way even if you have a bad tolerance value. Of course you will see the effects of a bad tolerance value from other applications or when you execute a SQL statement directly against your database.

So the metadata stored for a Oracle Spatial/Locator table are:

- Owner
- Table name
- Geometry column name (the metadata record will be replicated for several values because a table can have more than one geometry column)
- Dimension info (for each dimension: dimension name, max value, min value, tolerance)
- SRID (possibly NULL)

If you have a 3D vector layer (for example a 3D shapefile) I think you will not notice the third dimension while you work with views and layouts, but if you export that layer to your Oracle Spatial/Locator database, it will be stored with a 3D geometry column (you can see the number of dimensions of each using Sqldeveloper for example)

As you perhaps know, Oracle Spatial/Locator supports 4D geometries (XYZT, I think Oracle normally uses the letter T instead of M for the 4th dimension). When you open one of these tables with gvSIG, the resulting layer is a 3D layer (4th dimension is discarded)

I have never heard about a parameter called resolution in the table metadata. Perhaps you are talking about some operations that allow you to restrict the result by setting a min and max_resolution value, but this is not connected to tables' metadata.

I agree that it would be a good idea to let the user set the metadata values.

Regards,
Juan Lucas Domínguez Rubio
---
Prodevelop SL, Valencia (España)
Tlf.: 96.351.06.12 -- Fax: 96.351.09.68
http://www.prodevelop.es <http://www.prodevelop.es/> 
---

________________________________

De: gvsig_internacional-bounces at listserv.gva.es en nombre de Wolfgang Qual
Enviado el: jue 24/09/2009 8:59
Para: Users and Developers mailing list
Asunto: [Gvsig_english] Question on GeoBD and Metadata when exporting toOracle

Hi list,
in our City administration, different GIS software is used to work with
spatial data. Among them, ArcMap and gvSIG allow to access a central
oracle spatial database. Thanks to the great GeoBD extension, accessing
that database via gvSIG is very comfortable, even exporting new layers
to the database is possible.
Yesterday, a colleague of mine who is in charge of the overall design of
the geodatabase asked me to provide some details on GeoBD's
capabilities. He asked me about metadata that is created by that
extension when exporting a shapefile to the oracle spatial database and
possibilities to set custom settings for the metadata. In this context,
he also talked about "tolerance" (SDO_TOLERANCE_1, SDO_TOLERANCE_2),
"resolution". I have no idea, whether GeoBD sets these values.
Therefore, I would be very happy, if someone of you (maybe the
developers from Prodevelop) could give me some details on the type and
values of metadata that is written to new oracle spatial layers. That
would be very great to have.

Best regards and thank you very much for your help.
Wolfgang

--
Wolfgang Qual
Landeshauptstadt München
Referat für Gesundheit und Umwelt
RGU-UW 11
Sg. 1 Gesundheits- und Umweltberichterstattung,
Energie und Klimaschutz
Bayerstr. 28a, 80335 München
Tel.: +49 (0)89 233-477 17
Fax.: +49 (0)89 233-477 05
E-Mail: wolfgang.qual at muenchen.de

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