Re: [Orekit Developers] Problem with getPVCoordinates?

[Evan Ward <evan.ward@nrl.navy.mil>]

Alessandro,

If you use the following line instead do you still see the problem?

Frame earthFrame = FramesFactory.getITRF(IERSConventions.IERS_2010, false);

My guess is that the difference has to do with how Orekit caches and 
interpolates EOP data to speed computation. Using simple EOP is roughly 
equivalent to cm level accuracy in LEO. Hopefully Luc can chime in with 
error levels introduced by interpolating and shifting the frame 
transformations, but in one case I only noticed differences at the mm level.

Best Regards,
Evan

On 01/26/2017 07:54 AM, alessandro.vananti@aiub.unibe.ch wrote:
> I have a problem with the following code.
>
> Frame inertialFrame = FramesFactory.getEME2000();
> GeodeticPoint station = new GeodeticPoint(Math.toRadians(40),
> Math.toRadians(0), 0);
> Frame earthFrame = FramesFactory.getITRF(IERSConventions.IERS_2010, true);
> BodyShape earth = new
> OneAxisEllipsoid(Constants.WGS84_EARTH_EQUATORIAL_RADIUS,
> Constants.WGS84_EARTH_FLATTENING, earthFrame);
> TopocentricFrame staF = new TopocentricFrame(earth, station, "station");
>
> staF.getPVCoordinates(AbsoluteDate.J2000_EPOCH, inertialFrame);   // line to
> comment out
>
> System.out.println(staF.getPVCoordinates(AbsoluteDate.J2000_EPOCH.shiftedBy(1),
> inertialFrame).getPosition().getX());
>
>
> When I run it I get as a result: 866163.3982467309
> If I comment out the line "staF.getPVCoordinates(AbsoluteDate.J2000_EPOCH,
> inertialFrame);" then I get as a result 866163.3982467302.
> So the last digit is different. How is it possible?
>
> Alessandro