[postgis] SFSQL Metadata Views

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[postgis] SFSQL Metadata Views

Frank Warmerdam
Folks,

Some of the core capabilities of SFSQL are now being handled by PostGIS.
However, currently there is no real support for metadata of any kind.

The SF-SQL specification includes two "Feature Table Metadata Views":

 o GEOMETRY_COLUMNS: Associates geometry columns with a spatial reference
   system id, a geometry type (restricting the columns to lines for instance),
   and a dimension.

 o SPATIAL_REFERENCE_SYSTEMS: Associates spatial reference system id with
   their well known text equivelent.

The document also talks about AddGeometryColumn(), and DropGeometryColumn()
stored procedures, which would help maintain the above views when adding
a geometry column to an existing table.

My question then is, do we want to pursue implementation of GEOMETRY_COLUMNS
and SPATIAL_REFERENCE_SYSTEMS tables within PostGIS, and if so, what sort of
help in the form of stored procedures or other automation can we provide to
ensure they are maintained and consistent?

Also, who has experience with other SF SQL implementations? (Oracle? SDE?)
I want to get to the point that a client program can work with only minor
twiddles against PostGIS or some other SFSQL compliant database environment.
What do we need to make that happen?  Does anyone else implement and maintain
GEOMETRY_COLUMNS and SPATIAL_REFERENCE_SYSTEMS?  

Best regards,

---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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Re: [postgis] SFSQL Metadata Views

David Blasby-3
>However, currently there is no real support for metadata of any kind.
>
> The SF-SQL specification includes two "Feature Table Metadata Views":
>
>  o GEOMETRY_COLUMNS: Associates geometry columns with a spatial reference
>    system id, a geometry type (restricting the columns to lines for instance),
>    and a dimension.
>
>  o SPATIAL_REFERENCE_SYSTEMS: Associates spatial reference system id with
>    their well known text equivelent.
....


I've been looking into that today, and we could probably write some
triggers and stored procedures to keep GEOMETRIC_COLUMNS updated.

We'll need to have some way of restricting a GEOMETRY column to be, say,
a LINESTRING.  I dont want to have to read a system table on every
INSERT or UPDATE.  Any ideas?

We'll also have to do something with the Spatial Reference System.  I'm
actually looking at that right now since I want to add a length()
function that works on a ellipsoid.  

dave

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Re: [postgis] SFSQL Metadata Views

Frank Warmerdam
Dave Blasby wrote:
> I've been looking into that today, and we could probably write some
> triggers and stored procedures to keep GEOMETRIC_COLUMNS updated.
>
> We'll need to have some way of restricting a GEOMETRY column to be, say,
> a LINESTRING.  I dont want to have to read a system table on every
> INSERT or UPDATE.  Any ideas?

Dave,

Is it important that this be inforced all the time?  
 
> We'll also have to do something with the Spatial Reference System.  I'm
> actually looking at that right now since I want to add a length()
> function that works on a ellipsoid.

How are you wanting to deal with spatial reference systems?  I am assuming
that you don't want to build reprojection support into PostGIS, is that
right?  I have lots of C++ code for building, and parsing WKT spatial
refs, and a binding on PROJ.4 using them to reproject geometries.  This
is all in OGR.

Best regards,

---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, [hidden email]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

To unsubscribe from this group, send an email to:
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