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*To*: orekit-users@orekit.org*Subject*: Re: [Orekit Users] Covariance matrix after Least Squares estimation*From*: MAISONOBE Luc <luc.maisonobe@c-s.fr>*Date*: Thu, 17 Aug 2017 18:02:42 +0200*In-reply-to*: <sympa.1502983306.8469.733@orekit.org>*User-agent*: Internet Messaging Program (IMP) H5 (6.2.3)

alessandro.vananti@aiub.unibe.ch a écrit :

Hi all,

Hi Allessandro,

I use the BatchLSEstimator class to perform an orbit determination. The computed orbit is correct. Now I would like to see the covariance matrix of my orbit. I tried to use BatchLSEstimator.getOptimum().getCovariances() but the values seem to be wrong. They seem to be dependent from the scale factor introduced in NumericalPropagatorBuilder. Is there a way to obtain the standard covariance matrix?

Good catch! As the getOptimum() method returns a view of the low level mathematical object provided by the optimizer, all the data it contains is in the units as seen by the optimizer, i.e. rescaled.

scale exists but is not easy. Here is how you could do that: - get all the drivers for estimated orbital parameters by calling estimator.getOrbitalParametersDrivers(true) - get all the drivers for estimated propagators parameters by calling estimator.getPropagatorParametersDrivers(true) - get all the drivers for estimated measurements parameters by calling estimator.getMeasurementsParametersDrivers(true) - from these three lists, and in the retrieval order (i.e. orbit drivers, followed by propagators drivers, followed by measurements drivers), build an unscaling array by using driverslist.getDrivers(), and driver.getScale() - for each element (i, j) in the mathematical matrix from the optimum, you should get the corresponding physical element by multiplying (or dividing ?) by array[i] * array[j]. We should provide a convenience method in the estimator to do all these parameters retrieval, scale extraction and multiplication for users. Could you open a new issue in our forge (you have to register first, at <https://www.orekit.org/forge/projects/orekit>) so we do not forget to add this improvement? best regards, Luc

Any help is appreciated! Alessandro

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