Hello,

I am trying to calculate the along_track incidence angle for an IKONOS image so I can build RPCs using the "Build RPCs" tool. The documentation was helpful (https://www.harrisgeospatial.com/docs/parametersfordigitalcameraspushbroomsensors.html#incidence_angles), but the equation provided to calculate the along_track angle gives me a negative numerator. Because it has to be square-rooted, this gives a non-answer for the along_track incidence angle.

I interpreted the numerator for the along_track to be (a^2)*1 + tan^2(nominal) - 1. However, for my values of a (0.935484) and nominal (19.34332), this results in a negative numerator (-0.00164). If I pretend this value is positive, I only get an incidence angle of 1.69 (which seems low).

I also tried a few other interpretations of the along_track numerator that interpreted the extra 1 in the front of the equation as a form of factoring. The numerators for these were:
1) a^2 + (a^2 * tan^2(nominal angle - 1) (which results in a final angle of 35.74 degrees) and
2) a^2+ tan^2(nominal angle -1) (results in a final angel of 38.74 degrees).

Am I on the right track, or are there brackets missing somewhere in the equation? And if so, are there brackets missing in the across_track equation as well? I get a realistic answer (19.98 degrees) for the across track when the numerator is interpreted as tan^2(nominal)+1-a^2.

Thanks in advance for any suggestions.

Val