prem@geomag.fsu.edu (Prem Subrahmanyam) (08/08/89)
I am looking for an easy way to determine the range of latitudes and longitudes I am looking at, according to the following: I have a satellite, orbiting at R earth radii looking straight down at a particular longitude and latitude. The "wideness" of the lens angle can be determined by drawing a line from the eyepoint that is tangent to the earth. In other words, the field of view consists of a circle, where a line drawn in 3-space through the edge of the circle that I see will be tangent to the earth (don't bother about determining things due to a non-spheric earth--a spheric approximation will suffice). So, what is the range of latitudes and longitudes I'm looking at? The formula should contain 1. the distance of the satellite from the earth in earth radii. 2. the latitude and longitude that is directly beneath the satellite. The reason I'm asking is that we're using the NCAR plot package here on our Sun, and the contour plotting routine goes into an infinite loop if it attempts to do contours outside of the range of the present "window". We almost lost our filesystem due to the fact that the metafile had grown overnight to 77 MEGS....I need to determine the latitude and longitude range for a variety of altitudes so that our contouring program can run, given a specific altitude factor, and not have to be empirically assigned the lat and lon range for each different altitude. Oh, I forgot to mention that almost the entire earth is visible to the satellite at 6.63 earth radii...I mean almost the entire hemisphere that we're viewing...obviously not the entire earth. ---Prem Subrahmanyam p.s. this is a favor asked in repayment of the service we've provided by having our graphic files publically accesible.