PostGIS 2.5 is just around the corner. One of the new functions coming is the ST_OrientedEnvelop. This is something I've been waiting for for years.
It is the true minimum bounding rectangle, as opposed to ST_Envelope which is an axis aligned bounding rectable.
Below is a pictorial view showing the difference between the two.
Original Parcels |
Parcels with Envelopes |
Parcels with Oriented Envelopes |