I'm a student and I'm trying to compute the footprint of a generic EO sensor starting from sensor's characteristics and position and velocity vector of my satellite in ECEF coordinates. I followed this tutorial of Stephen Hartzell to compute the satellite line-of-sight intersection with Earth and validate the results comparing with the ones from STK.
It seems to work well when the satellite is Nadir pointing: the results (slant range, point on earth coordinates) differs about $10^{-8}$ from the STK ones. However, when I apply a pitch or roll rotation to the sensor boresight, the slant computed differs 27 meters from the STK ones with consequent significant errors (0.1°) to the latitude and longitude points computed from the intersection point coordinates.
To describe the procedure in detail, I've defined a unit vector pointing toward the Earth $(z = \frac{\llap{-}r}{|r|})$ from my ECEF coordinate. Therefore, I've moved that from ECEF to the satellite body coordinate system with the appropriate rotation matrix, and then I've applied my pitch/roll rotations around the proper axis. At this point, I converted the rotated pointing vector in ECEF coordinates, and I’ve applied the intersection procedure shown above.
Do you think this procedure is correct or there is another one more effective?
Thanks in advance.
