public NumberExpression<Integer> srid() {
        if (srid == null) {
            srid = Expressions.numberOperation(Integer.class, SpatialOps.SRID, mixin);
        }
        return srid;
    }
Returns the Spatial Reference System ID for this geometric object. This will normally be a
foreign key to an index of reference systems stored in either the same or some other datastore.

@return SRID
querydsl-spatial/src/main/java/com/querydsl/spatial/jts/JTSGeometryExpression.java