I would suggest you go with #1 or #2. The added complexity of method #3
probably won't pay any significant dividends in practical terms. You
could always implement #3 for version II. :-)
Will you be considering squint? Frankly, I'm not sure any current
satellites are using antennas where squint would play a part.
Regards...
On 03/25/2013 11:15 AM, Joseph Armbruster 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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--
73, de Gus 8P6SM
Barbados, the easternmost isle.
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