Inertial Measurement Unit (IMU)

What is a "megnatometer" ? What does it measure ? usually such units use accelerometers and gyros for the angular velocity, I never met the megnatometer.

It measure x and y axes of earth's magnetic field.

Then it is a "magnetometer " no? Words have a meaning and in communication an error can be fatal for the understanding. This is the reason you should check what you write before sending the message if not for anything else than respect for the reader.

Such a measurement will only give you the north -magnetic- which is not the north geographic and if you do not have corrections then you want to go to Greenland and come to the Fidgi Islands.

Your concept will lead to bigger errors since you will need 2 successive integrations to define displacement.