spherical trigonometry

[nelson61]

I'm working on building a Google Earth database of satellite footprints (those licensed by US) and could use some help for some special cases.

Some of the satellites data is in a form requring a fairly complex set of spherical trigonometric equations (excel spreadsheet) to solve the data points.

I've been chasing myself in circles for a couple of days trying to find an apparant error in my spreadsheet calculations (could be error in entry or could be a logic error).

If anyone would like to give me an assist, PM me and we can go into the details.

 

[B.J.]

I'm working on building a Google Earth database of satellite footprints (those licensed by US) and could use some help for some special cases.

Some of the satellites data is in a form requring a fairly complex set of spherical trigonometric equations (excel spreadsheet) to solve the data points.

I've been chasing myself in circles for a couple of days trying to find an apparant error in my spreadsheet calculations (could be error in entry or could be a logic error).

If anyone would like to give me an assist, PM me and we can go into the details.

Are you really trying to calculate "footprints", or just Az/El calculations? Ie footprints, which usually implies not just whether you have line of sight visibility, but also that the sat is actually beaming signal in your direction, require data only available to the satellite controllers and it's often different for different transponders on the satellite. I don't know any possible way you can do this unless you work for the company controlling the satellite. If it's just Az/El data you're trying to calculate, there are a number of documents on the web that have different ways of doing this. Some are easy provided that you have a good knowledge of the math, some are more laborious, but relatively straightforward. I used to have a fairly solid knowledge of the math, but that was some 45 years ago. Now, I have to use the laborious techniques.
If, however it's footprints, I don't know how you'd do that.

 

[nelson61]

I found my problem, a misplaced parenthesis. Yes, the derivation was initially published 40 or 50 years ago. It is all about a principal spherical coordinate system that relates to a secondary spherical coordinate system, the principle being at the center of the earth and the secondary at the center of the satellite. Back then, they used a mainframe to do the calculations. It reminds me of working with the the log tables in my Chemical Rubber Handbook (not fondly). Today, a spreadsheet can do it all.