[Kstars-devel] SatLib

Jason Harris kstars at 30doradus.org
Sun Jul 16 19:47:20 CEST 2006 

Hi Bernard!

Glad to hear this message.  It sounds like what you and I have done 
separately so far will fit together well.  I have written a 
SatelliteTrack class that stores the SkyPoints that make up a 
satellite's track in the sky.  I have also written a SatelliteComponent 
class to manage the currently-acive satellite tracks.

I'd be very happy to give you what I have so far and let you adapt it to 
your C++ library (which sounds very nice, BTW), unless you'd prefer 
another way?  Maybe I can just commit what I have so far to SVN...let me 
know.

Jason

Bernard GODARD wrote:
> Hi,
> 
> Oops, I was working on that too...
> 
> I guess, I should have written more often to the list (I just wrote
> once), but I am quite busy at the moment I am quite slow to code
> (always changing the interfaces to my libs..).
> 
> I made a C++ library for SGP4 (and other models) from a GPL C lib.
> It doesn't have global variables.
> You can find it here:
> http://godard.b.free.fr/dotclear/index.php?2006/05/26/4-sgp-cpp-library
> there's a small documenting test program inside
> 
> basically, it works like this :
> 
> _____________
> Sxpx * sat1;         // the Sxpx class is a pure virtual class that is used to
>                             // compute the position and velocity of a satellite
>                             // independantly of the model used (SGP,
> SGP4, SDP4, SGP8
>                             // or SDP8). The Sgp, Sdp4, Sgp4, Sgp8 and
> Sdp8 classes all
>                             // implement the Sxpx interface
> 
> string fname("sat.tle");  // the name of the file containing the TLE
> string id1("88888");      // a NORAD ID for a satellite
> 
> t = new Tle(fname,id1);  // open the file whose name is fname. Look in this file
>                                  // for the first TLE whose satellite
> NORAD ID is id1
> e = new SgpElements(*t); // convert the TLE from string to numerical data
> 
> sat1 = new Sgp(*e);         // create an SGP model with the TLE PosVel
> 
> pv=sat1->getPosVel(jd); // get satellite position and velocity at julian day jd
> // in the TEME reference frame of TLE epoch
> _______________________
> 
> I have been thinking that we need a new SkyComponents class with all
> the "active" satellites and I was working on a TleManager class that
> can read TLE files, add and remove satellites.
> 
> Well, I will be happy to help if I can.
> 
>            Bernard
> 
> 
> 
> 
> On 7/15/06, Jason Harris <kstars at 30doradus.org> wrote:
>> Hi Jean-Baptiste,
>>
>> I have finally begun work on adding earth satellites to KStars using your
>> SatLib framework.  If you don't mind, I'd like to give some feedback on the
>> API to hopefully make a future version of the lib a little more usable for
>> KStars.
>>
>> First, a brief introduction to your library for my fellow KStars devs:
>>
>> The two main functions for our purposes are:
>>
>>    int SatInit(char *ObsName, double ObsLat, double ObsLong, double ObsAlt,
>> char *TLE_file);
>>    int SatFindPosition(char *satname, double jd_start, double step, long
>> number_pos, SPositionSat *pPositionSat[]);
>>
>> SatInit() reads in all of the satellites' orbital data from the TLE_file and
>> creates the global sat array to hold these data.  It also sets up the
>> geodetic position of the observing station.
>>
>> SatFindPosition() returns an array of SPositionSat structs, which basically
>> encode the instantaneous Azimuth/Elevation coordinates for the named
>> satellite, for a series of instants, starting at jd_start.
>>
>> So, the usage pattern is to first call SatInit() and then call
>> SatFindPosition() on each satellite for which you want a track.
>>
>> Now, my comments:
>>
>> *) Is it possible to decouple the initialization of the satellite orbital data
>> from the initialization of the geographic position?  Ideally, I'd like to
>> call SatInit() once when KStars starts up, and then be able to react when the
>> user changes their geographic position without reading the orbital data all
>> over again.  Maybe the geographic position data would make more sense as
>> arguments to SatFindPosition() than SatInit() ?
>>
>> *) Maybe this is just my prejudice as a C++ guy, but it seems kind of
>> dangerous to have global variables with simple names like "sat".
>>
>> *) Can there be a version of SatFindPosition() that returns Equatorial
>> coordinates rather than Horizontal?  This isn't a big deal; we have functions
>> to do the conversion, of course.  Also, do you correct for atmospheric
>> refraction in determining the elevation coordinate?
>>
>> *) What are the units for the ObsAlt parameter of SatInit()?  Is it the height
>> above sea level, or the distance from Earth's center?
>>
>> thanks for your efforts!
>>
>> Jason
>>
>> On Sunday 25 September 2005 06:35, jb wrote:
>>> Hi all :)
>>>
>>> On a previous mail, I've told developping a C library for position
>>> satellites calculation.
>>>
>>> This job will be done on 8-9 October week end ;) (a good code week end)
>>>
>>> What's the aim ?
>>> Having a strong, fast and light C library that gives Ra & Dec of a
>>> satellites, by given TLE, position and time.
>>>
>>> To do what ?
>>> search what satelites you've seen last night, predict ISS pass on Sun or
>>> moon...
>>>
>>> Why not include this on Kstars code ?
>>> We want to share it with all other ephemerids program (cartes du
>>> ciel/Skycharts for example)
>>>
>>> A Little problem :
>>> we aren't really good programmers ;) but we'll be helped by Patrick
>>> Chevalley to do this.
>>>
>>> If you have any asks, hints, clue, code to do this, please send me a mail
>>> to this adress.
>>>
>>> Mail you soon,
>>>
>>>                                       Jean-baptiste BUTET
>>>
>>>
>>>
>>> _______________________________________________
>>> Kstars-devel mailing list
>>> Kstars-devel at kde.org
>>> https://mail.kde.org/mailman/listinfo/kstars-devel
>> --
>> -------------------------------
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>> Forums: http://kstars.30doradus.org
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