That's a best-guess, assuming that the text is referring to how the terrain is being handled by the point-of view function -- specifically, that the geographical features are not "flattened out" as the Mobile Object flies over them. Thus, "without forced flattening, the MO follows [or "is influenced by"] the terrain, in terms of pitch and roll." (These last two terms, of course, refer to the motion of the aircraft about one of its axes. Pitch refers to the up-and-down motion of the nose and tail of the aircraft about the horizontal axis that joins the ends of its wings, and roll is the motion of the aircraft about the horizontal axis that joins the nose and the tail.)