[amsat-bb] Re: satellite los footprints

[Joseph Armbruster]

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:
> 
> 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 <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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