I'm about to start a project on making my first autopilot! From what I've read so far, thermopiles are fairly accurate and not susceptible to noise such as vibration whereas the IMU is. However, from most autopilots that I've seen, neither are used together for attitude estimation (i.e. they seem to be only used separately). I thought it would be great if the sensor drift from the IMU could be fused with somewhat reliable data from the thermopiles. Am I looking at it wrongly or is there a reason why this isn't commonly implemented?