I need to calculate a GPS azimuth under the following conditions (diagram below). What I have is a known GPS location and bearing (azimuth of 145.56°). At this known position and orientation I also know that my field of view is centred on this azimuth and is 12° in total i.e. 6° of view either side of this azimuth. I want to calculate the azimuth if I changed my bearing to travel along the extremes of this field of view. What I have been doing is a really simple calculation of 145+6 and 145-6 to give me my requirements, however I am not at all confident that it is this simple. I think both degree systems being calculated may not be compatible as the azimuth is spherically related and the field of view if planar. Any advice, direction, help would be greatly appreciated.