IsSimple(g)

Currently, this function is a placeholder and should not be used. If
implemented, its behavior will be as described in the next paragraph.

Returns 1 if the geometry value g has no anomalous geometric points,
such as self-intersection or self-tangency. IsSimple() returns 0 if the
argument is not simple, and -1 if it is NULL.

The description of each instantiable geometric class given earlier in
the chapter includes the specific conditions that cause an instance of
that class to be classified as not simple. (See [HELP Geometry
hierarchy].)

URL: http://dev.mysql.com/doc/refman/5.5/en/geometry-property-functions.html#general-geometry-property-functions

