[amsat-bb] Re: satellite los footprints
kb1lqd at gmail.com
Mon Mar 25 10:58:10 PDT 2013
There is so much variability in the footprint that #1 or #2 would probably
suffice. Working satellites on the fringes of AOS and LOS wheigh heavily on
your location, surroundings, and equipments that it's impractical, it's
just a visual "references" that shows relative satellite reception.
Hope this helps.
- Brent, KB1QD
On Mon, Mar 25, 2013 at 11:15 AM, Joseph Armbruster <
josepharmbruster at 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
> 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
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