属于此组的每个函数都以几何值作为参数，并返回该几何的某些定量或定性属性。有些函数会限制其参数类型。如果参数的几何类型不正确，此类函数将返回 NULL。例如，ST_Area() 多边形函数在对象类型既不是 Polygon 也不是 MultiPolygon 时会返回 NULL。Each function that belongs to this group takes a geometry value as its argument and returns some quantitative or qualitative property of the geometry. Some functions restrict their argument type. Such functions return NULL if the argument is of an incorrect geometry type. For example, the ST_Area() polygon function returns NULL if the object type is neither Polygon nor MultiPolygon.