[amsat-bb] Re: satellite los footprints

[Brenton Salmi]

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
> 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
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