Economc rent & opportunity cost versus consumer & producer s versus, why, horizontal, economic, triangle

farrukhsadiq

I am wondering why economic rent & opportunity cost are differently calculated than consumer surplus & producer surplus.
page 46.
consumer surplus: upper left triangle from horizontal line of equilibrium and demand curve
producer surplus: lower left triangle from horizontal line of equilibrium and supply curve
page 293:
economic rent: lower left triangle from horizontal line of equilibrium and supply curve
opportunity cost: lower right triangle from supply curve and vertical line of equilibrium
On the abscissa you have in both cases the quantity and on the ordinate in both cases the price (wage rate). So, why can’t you calculate them not in the same why?
What do I miss?
Andreas