Re: [Orekit Users] Newbye question on how to get satellite location given a TLE

Thank you for your super fast reponses!!

Here you are what I have done in order to get altitude, latitude and longitude of sat: http://codepaste.net/horgh2

I have compared results with satview.org for OSCAR 7 AO-7:

Mine:

date: 2014-03-10T19:24:00.000

altitude: 1453.9749291524224

latitude: 24.804338612981198

longitude: -49.60234374328559

Satview.org:

date: 2014-03-10T19:24:08.000

altitude: 1451.68

latitude: 25.63

longitude: -49.47.

TLE data for this sat is the latest I can get from http://www.celestrak.com/NORAD/elements/amateur.txt

Can this difference be acceptable (given that satview could be a good reference).. or there is a mistake of mine?

Thank you very very much!

Marco

2014-03-10 17:30 GMT+01:00 MAISONOBE Luc <luc.maisonobe@c-s.fr>:

Hi Marco,

Marco Serioli <mserioli@gmail.com> a écrit :

Hi and compliments for your super project!

Thanks a lot for these kind words.

I'm a newbye and moreover I know nothing about background concept of this
project.

I'm simply developing a software in which I have to find azimuth and
elevation of a Satellite at a given time from a given Ground Station.
Moreover I want to find Satellite lat and long.

What I have tryed to do is: after setting OREKIT_DATA_PATH, create a TLE
object

TLE tle = new TLE(
"1 07530U 74089B 14068.85842801 -.00000028 00000-0 96998-4 0
9129",
"2 07530 101.4628 53.9967 0012290 127.9050 292.4577
12.53603117799073");

TLEPropagator propagator = TLEPropagator.selectExtrapolator(tle);

But I have not found a way to create a ground station.

You can use TopocentricFrame for this, and even better ElevationDetector (which is built from a topocentric frame) if you want to automatically display start and end of visibilities from this specified station. You can look in the src/tutorials folder in the source distribution (fr.cs.examples.propagation.VisibilityCheck).

Moreover I can get
only PVCoordinates from propagator and I don't know how to get relative
angular coordinates to plot satellite position projected on a world map.

In order to display geodetic coordinates, you can look at another tutorial: MasterMode. There, you will see a local implementation of OrekitFixedStepHandler. Copy it and replace the print part in the handleStep with a new print dedicated to geodetic coordinates. In order to compute these coordinates, you would have first created a model for Earth as follows:

Frame earthFrame = FramesFactory.getITRF(IERSConventions.IERS_2010, true);
BodyShape earth = new OneAxisEllipsoid(Constants.WGS84_EARTH_EQUATORIAL_RADIUS,
Constants.WGS84_EARTH_FLATTENING,
earthFrame);

and then in the handleStep method you can do:

GeodeticPoint gp =
earth.transform(curentState.getPVCoordinates().getPosition(),
currentState.getFrame(),
currentState.getDae());

Then you can print gp.getLatitude(), gp.getLongitude(), get.getAltitude().

How can I get information requested?

You should browse the tutorials and look at <https://www.orekit.org/forge/projects/orekit/wiki>.

Thank you and sorry if my question is silly

No problem, you're welcome
Luc

Marco

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