# FOG Yaw Gyro, transformation to remove earths rotation based on attitude (roll,pitch,yaw,latitude)

I'm trying to use an accurate FOG gryo for tracking heading in a moving platform. The FOG gyro has two rate errors, Faraday (fixed amount regardless of alignment to the earth) and the 15.04 degrees per hour of the earths rotation (function of my alligmnet to the rotation).

I know the attitude of the gyro ring.. Roll,Pitch,Yaw and Latitude,Longitude.. If the gyro is exactly aligned with the rotation I will see all of the 15.04 deg/hr superimposed, none of it if I'm perpendicular to the rotation. Now I need mapping/function that will give me a number between -1 to 1 giving me the amount of the earths rotation imparted at a given roll,pitch and yaw on the surface of the earth.. Where roll=pitch=0 level with the surface, yaw=0 pointing true north. The gyro (yaw axis) is mounted flat in the plane of the earth.

This will allow me to remove the Faraday drift (constant) and then calculate the amount of the earths rotation projected into this gyro at this roll,pitch, yaw, latitude.

Can someone help with this transformation or point me to a document that can help?

• That's what I would have expected; I should perhaps have phrased my question as, "how does the level of accuracy and precision required to detect the earth's rotation in various lengths of time compare to what's available from various gyros?" For example, if one wanted a device which could report its latitude if left at in a fixed earth-relative position, in a temperature-controlled space, for 48 hours, would such a device require $1,$10, $100,$1000, or more worth of sensors? – supercat Nov 26 '13 at 16:09