Coordinate Transformation in Quadrotor

[danish.umer.k]

Hello... I am about to start my work on quadrotor for my university final year project. I am stuck at the very basic concepts in its mathematical modeling. They say that since the quadrotor possesses all 6 degrees of freedom, you have to transform its coordinates from body-fixed frame to earth-fixed frame of reference by multiplying with a rotation matrix called the direction cosine matrix. I have tried very hard but I am still unable to exactly grasp the concept. I mean why do u need to carry out the transformation at all why cant u just process the sensor information using the on-board controller. I will deeply appreciate any kind of guidance.
Thanks in advance.