On the sphere, an equality relationship is rarely used. There
are frequently questions like Is object
a contained by object
b? or Does object
a overlap object
b?
pgSphere supports such
queries using binary operators returning
true or false:
Table 5.2. Contain and overlap operators
| operator | operator returns true, if |
|---|---|
| <@ or @ (deprecated, not for smoc) | the left object is contained by the right object |
| @> or ˜ (deprecated, not for smoc) | the left object contains the right object |
| !<@ or !@ (deprecated, not for smoc) | the left object is not contained by the right object |
| !@> or !˜ (deprecated, not for smoc) | the left object does not contain the right object |
| && | the objects overlap each other |
| !&& | the objects do not overlap each other |
An overlap or contain operator does not exist for all
combinations of data types.
For instance, scircle <@ spoint is
useless because a spherical point can never contain a
spherical circle.
When one of the arguments of such an operator is a MOC and the other is an scircle or an spoly, the non-MOC argument is converted to a MOC of the order of the maximum order of the MOC. When comparing against a MOC-valued column, it is usually much faster to explicitly convert the geometry using the smoc constructor, as the conversion will then only happen once.
Example 5.3. Is the left circle contained by the right circle?
sql> SELECT scircle '<(0d,20d),2d>' <@ scircle '<(355d,20d),10d>' AS test ;
test
------
t
(1 row)
Example 5.4. Are the circles overlapping?
sql> SELECT scircle '<(0d,20d),2d>' && scircle '<(199d,-10d),10d>' AS test ;
test
------
f
(1 row)
Example 5.5. Overlaps between a circle and a moc
sql> SELECT scircle '<(37d, 5d), 0.25d>' <@ smoc('4/1117') AS test ;
test
------
f
(1 row)
Example 5.6. Overlaps between a circle and a moc with explicit order
sql> SELECT scircle '<(37d, 5d), 0.25d>' <@ smoc('4/1117 5/') AS test ;
test
------
t
(1 row)
Example 5.7. Overlaps between a circle and a moc with explicit cast (normally faster)
sql> SELECT smoc(5, scircle '<(37d, 5d), 0.25d>') <@ smoc('4/1117 5/') AS test ;
test
------
t
(1 row)