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Tip #3: What object is that?
In Oracle, if I want to know what type of SDO_Geometry object is stored in a column I can do the following:
gis@XE> select a.geom.get_gtype(), count(*) 2 from tas_lga a 3* group by a.geom.get_gtype(); A.GEOM.GET_GTYPE() COUNT(*) ------------------ ---------- 3 9 7 20
However, we have to be able to “interpret” the returned value from get_gtype() in order to understand what the numbers mean. So, let’s “tart up” the output …
gis@XE> select case a.geom.get_gtype() 2 when 1 then 'Point' 3 when 2 then 'Linestring' 4 when 3 then 'Polygon' 5 when 4 then 'Collection' 6 when 5 then 'MultiPoint' 7 when 6 then 'MultiLineString' 8 when 7 then 'MultiPolygon' 9 when 8 then 'MultiCollection' end as gtype 10 count(*) as Total 11 from TAS_LGA a 12* group by a.geom.get_gtype(); GTYPE TOTAL --------------- ---------- Polygon 9 MultiPolygon 20
But for SQL Server 2008 there is an OGC 1.1 SQL method called STGeometryType() that will return the geography type as follows:
select a.geom.STGeometryType() as gtype, COUNT(*) as Total from dbo.TAS_LGA a group by a.geom.STGeometryType();
gtype Total
MULTIPOLYGON 20
POLYGON 9
Adding in dimensionality
Often though we want to know something about the dimensionality of a geometry column. This is pretty easy thing to query out in both databases.
Oracle
With Oracle there are two different geometry functions you can use to query the dimensionality of an sdo_geometry object. One – Get_Dims() – is Oracle specific; the other is part of the SQL3/MM standard – ST_CoordDim():
gis@XE> select a.geom.get_dims(), a.geom.st_coorddim(), count(*) 2 from TAS_LGA a 3* group by a.geom.get_dims(), a.geom.st_coorddim() gis@XE> / A.GEOM.GET_DIMS() A.GEOM.ST_COORDDIM() COUNT(*) ----------------- -------------------- ---------- 2 2 29
SQL Server 2008
select A.geom.STDimension() as dimension, count(*) as Total from dbo.TAS_LGA A group by A.geom.STDimension();
dimension Total
2 29
I hope these tips are useful.
Documentation
- MySQL Spatial General Function Documentation
- Oracle LRS Object Documentation
- Oracle Spatial Exporter Package Documentation
- Oracle Spatial Object Function Documentation
- Oracle Spatial Object Function Documentation (Multi Page Version)
- PostGIS pl/pgSQL Function Documentation
- SC4O Oracle Java Topology Suite (Stored Procedures) Package Documentation
- SQL Server Spatial General TSQL Function Documentation
- SQL Server Spatial LRS TSQL Function Documentation