Ken,
I have already implemented the concept of ground station, albeit, i'm not sure I like the way I have the configuration file set up, see:
ground station implementation: Google Earth Satellite Tracker - Ground Stations U... los implementation: Google Earth Satellite Tracker - Line of Sight Upd...
I'm likely going to implement 1 and move on for now. With respects to the ground station, I like the idea of having a minimum elevation angle, that would be insanely easy to implement. Expect these two to be implemented later tonight :-)
Joseph Armbruster
On Mar 25, 2013, at 6:42 PM, Ken Ernandes wrote:
My humble suggestion:
- Implement option 1 for the satellite footprint.
- 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 josepharmbruster@gmail.com 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 AMSAT-BB@amsat.org. 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