Re: [Orekit Users] Howto: Moving LLA Point Transformation?

[Luc Maisonobe <Luc.Maisonobe@c-s.fr>]

Hi James,

Le 20/08/2015 22:11, schatzman-james@n-ask.com a écrit :
> I can do something like
> 
>             earthRefFrame = getItrfFrame();
>             earth = new
> OneAxisEllipsoid(Constants.WGS84_EARTH_EQUATORIAL_RADIUS,
>                     Constants.WGS84_EARTH_FLATTENING,
>                     earthRefFrame);
>             TopocentricFrame staF = new TopocentricFrame(earth, lla, "anon");
>   PVCoordinates pv = staF.getTransformTo(frame,
> dateTime).transformPVCoordinates(      PVCoordinates.ZERO);
> 
> 
> to compute the position and velocity  in an arbitrary frame corresponding to a
> GeodeticPoint lla.
> 
> However, suppose the point is moving in the geodetic frame. There does not
> seem to be an analogous class to TopocentricFrame that allows for motion in
> the local coordinate system.
> 
> Short of some numerical approximation (e.g. finite differences), how can I
> compute the velocity in a new coordinate system of a point moving in LLA?

You are right, there were no derivatives associated with GeodeticPoint.
I have therefore just added a new signature in the
OneAxisEllipsoid.transform method to also provide two double arrays (one
for godetic coordinates first derivatives, one for the second
derivatives). See
<https://www.orekit.org/forge/projects/orekit/repository/revisions/ef1bb1a875f943f478209008c6da94d91848684e>.
For now, only the computation from geodetic point to Cartesian is available.

Does this meet your needs?

best regards,
Luc

> 
> Thanks!
>