A method for controlling an engine having a variable geometry mechanism, comprising: determining a first pressure at an inlet of the engine; determining a pressure ratio between the first pressure and a predetermined reference pressure; determining an output power for the engine; adjusting the output power based at least in part on the pressure ratio to obtain a corrected output power; generating a position control signal for the variable geometry mechanism (51,52) of the engine based on the corrected output power and the pressure ratio; and outputting the position control signal to a controller of the engine to control the variable geometry mechanism, wherein the position control signal is a first position control signal, and the variable geometry mechanism is a first variable geometry mechanism associated with a first spool compression system, and further comprising: determining an output torque for the engine; adjusting the output torque based at least in part on the pressure ratio to obtain a corrected output torque; determining a first temperature at the inlet of the engine; determining a speed of a second spool compression system, the second spool compression system being separate from the first spool compression system; adjusting the speed of the second spool compression system based at least in part on the first temperature and a reference temperature to obtain a corrected speed; generating a second position control signal for a second variable geometry mechanism of the engine based on the corrected output torque and the corrected speed, the second variable geometry mechanism being associated with the second spool compression system; and outputting the second position control signal to the controller to control the second variable geometry mechanism. determining a first pressure at an inlet of the engine; determining a pressure ratio between the first pressure and a predetermined reference pressure; determining an output power for the engine; adjusting the output power based at least in part on the pressure ratio to obtain a corrected output power; generating a position control signal for the variable geometry mechanism (51,52) of the engine based on the corrected output power and the pressure ratio; and outputting the position control signal to a controller of the engine to control the variable geometry mechanism, wherein the position control signal is a first position control signal, and the variable geometry mechanism is a first variable geometry mechanism associated with a first spool compression system, and further comprising: determining an output torque for the engine; adjusting the output torque based at least in part on the pressure ratio to obtain a corrected output torque; determining a first temperature at the inlet of the engine; determining a speed of a second spool compression system, the second spool compression system being separate from the first spool compression system; adjusting the speed of the second spool compression system based at least in part on the first temperature and a reference temperature to obtain a corrected speed; generating a second position control signal for a second variable geometry mechanism of the engine based on the corrected output torque and the corrected speed, the second variable geometry mechanism being associated with the second spool compression system; and outputting the second position control signal to the controller to control the second variable geometry mechanism. determining an output torque for the engine; adjusting the output torque based at least in part on the pressure ratio to obtain a corrected output torque; determining a first temperature at the inlet of the engine; determining a speed of a second spool compression system, the second spool compression system being separate from the first spool compression system; adjusting the speed of the second spool compression system based at least in part on the first temperature and a reference temperature to obtain a corrected speed; generating a second position control signal for a second variable geometry mechanism of the engine based on the corrected output torque and the corrected speed, the second variable geometry mechanism being associated with the second spool compression system; and outputting the second position control signal to the controller to control the second variable geometry mechanism.