SpatialDB Advisor: Tip #3: What object is that?

Tip #3: What object is that?

· Nov 24, 03:22 pm by Simon Greener

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.

— Isaac Kunen Nov 24, 03:37 pm #

<<Tip #2: Spatial Indexing and Primary Keys >>Tip #4: What Coordinate System is that?

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