My humble suggestion: 1. Implement option 1 for the satellite footprint. 2. If you decide to give the users the ability to input their location, them the option to provide either a single minimum elevation angle or a local map -- i.e., 360 individual minimum elevations as a function of Azimuth. It's much easier to project this and the user is generally interested in an unobstructed LOS with respect to his/her location.
73, Ken N2WWD Sent from my iPad On Mar 25, 2013, at 11:15 AM, Joseph Armbruster <[email protected]> wrote: > > I can not decide how to implement ground footprints with my google earth > satellite tracker. I figured, since I can't make up my mind, I should get a > second (and third, and fourth) opinion. For this thread, I would like to > discuss how satellite ground-footprints should be implemented. A quick > brainstorm led me to three possible implementations (I am leaning towards 3). > For each of these, I assume that a geographic line-of-sight footprint is > desired with no RF characteristics taken into consideration: > > option 1 : assume a spherical earth model and project a polygon downwards > towards the footprint > > - note: this is obviously the easiest approach but will result in the most > error > > option 2 : assume an ellipsoidal earth model and project an irregularly > shaped polygon downwards towards the footprint > > - note: this is arguably more difficult than option 1 and would result in > less error > > option 3 : use a digital elevation model and an ellipsoidal model to cull-out > regions that are not visible due to geographic features and project an > irregularly shaped polygon downwards towards the footprint > > - note: In this case, our footprint polygon would have holes cut out for the > regions that are culled out by mountain ranges, canyons / etc... Obviously, > this would be the most difficult to implement but would likely be the best > visual representation. The problem is, I would never dream of distributing > DEMs for the entire Earth with my tool, even DTED0 would be absurd in my > opinion. I could make the elevation queries accessible using a web-service, > but then the user would be tied to the internet. The other option would be > to allow the users to download their elevation data into a cache, then the > tool would just load / use it. This way the user would only have to obtain > the elevation data for their region of interest. Maybe that would be the > best approach? I am open to suggestions! > > If you have any experience visualizing footprints, please let me know. I > would be interested in hearing your lessons-learned. These are what the > line-of-sight indicators look like right now: Google Earth Satellite Tracker > - Line of Sight Update > > I am open to comments and suggestions, > Joseph Armbruster > _______________________________________________ > Sent via [email protected]. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
