Category Archives: INS

PHI or PSI: 2 flavours of error propagation models

In order to be able to write a Kalman filter for your INS, you have to derive a linear error propagation model for your navigation system. In the existing literature, such error propagation models are broadly categorized into 2 groups. … Continue reading

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Zero motion detector for inertial sensors

Zero motion detection for low cost MEMS units is an extremely important topic that has not received enough attention in the navigation community. For most low-cost inertial navigation applications, the only aiding source that can be used to limit the … Continue reading

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On the singularity of the attitude representations

How many times have you read this statement in a paper related with the inertial navigation: “…because of the singularity problem of Euler angles, quaternion representation is used in this study…” It looks quite a legitimate statement, doesn’t it. It … Continue reading

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Sampling Analog Inertial Sensors

In serious navigation projects, analog inertial sensors must be preferred instead of sensors with digital outputs. Some form of analog to digital converter (ADC) is required in order to read the outputs from these analog sensors. Selection of a proper … Continue reading

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A note on the strapdown algorithms

Probably you have noticed that the strapdown implementations in the toolkit directly use the sensor outputs to compute the body updates. For instance, accelerometer outputs (a) are multiplied by the DCM (C) and then added to the velocity state. Those … Continue reading

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Implementing a GPS/INS without a math-coprocessor

Recently, I have implemented (embedded) a GPS-INS system in the native environment of my Android phone (a 2.5 years old HTC Hero). The embedded navigation code is capable of processing external inertial sensor and GPS outputs sent to the device … Continue reading

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