In doing some testing of DWITHIN with DB2, I found that it does not
support the use of a units parameter in a query using a query like:
query = new Query( "CUSTOMERS", CQL.toFilter("DWITHIN(GEOM,
POINT(-121.914 37.311), 1.0, kilometers)") );
DB2 uses the distance value assuming it is in the coordinate system
units which in this case are decimal degrees which returns a very
different result from what is expected.
I've been able to correct the DB2 filter so that it produces the
expected result although I'm not sure if this would change any current
users of DWITHIN with the expectation that the units are ignored.
It appears that CQL.toFilter() supports only the following values
"\"feet\"",
"\"meters\"",
"\"statute miles\"",
"\"nautical miles\"",
"\"kilometers\"",
It does not support a filter without one of these values.
In poking around the source for other JDBC drivers, it seems that some
ignore the units and others support different units from those allowed
by CQL.toFilter().
The PostGIS code appears to support the following units:
put("kilometers", 1000.0);
put("kilometer", 1000.0);
put("mm", 0.001);
put("millimeter", 0.001);
put("mi", 1609.344);
put("miles", 1609.344);
put("NM", 1852d);
put("feet", 0.3048);
put("ft", 0.3048);
put("in", 0.0254);
However it doesn't support "statute miles" or "nautical miles".
CQL.toFilter() doesn't support plain "miles".
The Oracle code appears to support the following units:
put("metre", "m");
put("meters", "m");
put("kilometers", "km");
put("mi", "Mile");
put("miles", "Mile");
put("NM", "naut_mile");
put("feet", "foot");
put("ft", "foot");
put("in", "inch");
A similarly inconsistent set of units.
Is there a logical explanation for this?
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