# Need to clear some concepts: AHRS - Attitude - Yaw,Pitch and Roll - MARG sensors -INS

I faced the following terms : AHRS - Attitude - Yaw,Pitch and Roll - MARG sensors

I know for example how to calculate Yaw,Pitch and Roll , but does it related to Attitude ?

What's Attitude any way and how it get calculated ?

AHRS "Attitude and heading reference system" does it formed from Yaw,Pitch and Roll ?

MARG(Magnetic, Angular Rate, and Gravity) ? how it's related to other terms ?

My questions here are about these concepts, and there meaning , how they cooperate with each other , how they got calculated and which sensors suits for what ?

– Paul
Commented Aug 30, 2014 at 22:36
• I got confused , each time the same terms are used , they are mixed ! Commented Aug 30, 2014 at 23:11

When talking about vehicles (such as aircraft), attitude is just a fancy word for "orientation": the combination of yaw, pitch, and roll. These would be easy to calculate if the plane was just standing still; you'd use a compass to get the yaw, and a plumb bob to measure the pitch and roll. However, the acceleration or deceleration of the aircraft would severely alter these measurements.

• Gyroscopes measure angular velocity but can't measure position, velocity, or acceleration. (Fortunately, they aren't affected by it either.)
• Accelerometers can measure the force on an object (either real forces like gravity or perceived forces like centrifugal force). This measurement is often integrated to estimate velocity, or double-integrated to estimate position (both of which become increasingly inaccurate with time).
• Magnetometers measure the magnitude and direction of magnetic fields.

Regarding the other terms: IMUs produce some subset of MARG data (some have more sensors than others). MARG data is used by an AHRS system to compute attitude (roll, pitch, yaw). MARG data (optionally combined with other sensor data) is used by an INS system to compute both attitude and position.

Summarized from wikipedia:

IMU: (inertial measurement unit) is just a sensor that provides raw data to help determine velocity, acceleration, and orientation. It is usually some combination of an accelerometer, gyroscope, and a magnetometer. I emphasize that the IMU only provides raw data, and not necessarily the true information that you want.

MARG: is a general term for the kind of data obtained from an IMU: magnetic (magnetometer), angular rate (gyroscope), and gravity (accelerometer). A MARG sensor is an IMU that obtains all three of these pieces of data. But generally speaking, IMU's may also provide other data such as temperature and pressure (both can be used to help determine altitude).

AHRS: combines an IMU with some sort of processor that produces the useful information that you really need (i.e. roll, pitch, yaw, etc...). This is usually done by means of a (extended) kalman filter.

INS: is a complete system that enables you to determine and monitor the movement of an object over time, using the processed MARG data from that object.

To understand the relation between attitude and "roll, pitch and yaw", refer to my other answer:

What's the difference between Yaw and Attitude in Quad Rotor