Integrating the acceleration data two times will also integrate the measurement errors that occur in the accelerometer and gyroscope data. Moreover, effects of random noise and offset will also affect the displacement computation. This will result in inaccurate values of displacement.
It is advisable to fuse data from both inertial sensors and GPS to obtain pose and hence displacement.
To know how to determine pose using inertial sensors and GPS, refer to the following link:
