imuSensor - why is the acceleration negated, when calculating the total acceleration?

The IMU-Sensor simulates an acclerometer, magnetometer and gyroscope. As inputs the sensor needs acceleration, angular velocity and orientation. I don´t

understand why the input acceleration is negated.

https://www.mathworks.com/help/fusion/ref/imusensor-system-object.html

Answer 1

[Adam Danz]

Acceleration due to gravity is always negative. For example, if a falling object is affected only by gravity, its acceleration is -9.81m/s^2.

The sign of acceleration indicates the direction of acceleration for some reference frame. For example, if you're driving forward and you define forward as positive, then negative acceleration is the same as deceleration. The acceleration is being applied to the backward direction.

[Sebastian Bilkey]

thank you for your answer. your response does not really answer my question, but I already find the response somewhere else.

[Adam Danz]

@Sebastian Bilkey, please share what you've found so future visitors of this thread can benefit from your question. You can add it as a new answer.

[Morten Nissov]

I think he's asking why the following produces a negative number

>> imu = imusensor('accel-gyro');
>> imu([1,0,0], zeros(1,3))

ans =

   -1.0000         0    9.8100
   

Going from your explanation, and the accel begin in NED frame, I interpret the "true acceleration" being positive in the x axis as corresponding to the vehicle accelerating forward, as such I can't quite see why the measurement should be negative?

Especially considering "negative acceleration is the same as deceleration"