Tilt is the calculated look angle away from a straight nadir (straight down below the spacecraft) view. If the tilt exceeds a certain angle, 55 degrees, then "HO" in the TILT field indicates that the look angle is very oblique and the horizon is probably visible. Although the field is now calculated from the spacecraft location data whenever it is available, it was input by hand for many years. When the cataloger looks at the image, they indicate that the horizon was visible, by entering "PAN-" at the beginning of the feature field. If "PAN-" is at the beginning of the feature field, then the tilt field is constrained to be "HO."
Metadata: Camera Tilt