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();
------------------ ----------
                 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
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.


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> /
----------------- -------------------- ----------
                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.