Installation pitch tilt

Hello everyone
I did an experiment with a gps / ins system installed on a platform, with some tilt in the pitch axis, and now I’m trying to figure out how it affects the roll and yaw measurements. I guess this is a rotation matrix, which convolve in a super position the yaw and roll of the platform with certain weights (sin and cos) for the yaw and roll of the ins.
Am I right?

Thanks for help!
Aviel