Returns the minimum extent of the object in the Z direction, this can be combined with GetObjectSizeMaxZ to determine the size of the object in the Z direction. Note that the object may be off center so its min value may be 10 whilst its max value is 12, meaning its size is 2 units in the Z direction. This command takes the bounds of all meshes that make up this object, to check the bounds of a single mesh use GetObjectMeshSizeMinZ.
float GetObjectSizeMinZ( objID )