Re: [Orekit Users] Questions about updating orekit-data.zip

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

Hi Craig,

On 18/07/2012 23:56, Craig E. Ward wrote:
> According to the wiki, the static data in the version of orekit-data.zip
> available at the website isn't up-to-date. People needing to use Orekit
> need to use update this file themselves.

Yes.

> 
> What isn't clear to me is just how to do that. I can follow the link on
> the configuration page, but the page at the end of the link has many
> choices. I don't know which one is appropriate.
> 
> If I were to download one of the "EOP 08 C04 (IAU1980)" files, where
> would I put it in the orekit-data.zip hierarchy? Would it replace
> existing file(s) or just augment them?

If what you want is simplicity, I would suggest you to download two
files only and remove all other eop or bulletinb files from the zip.

The two files would be:

 <http://data.iers.org/products/12/1386/output/116590/finals.daily.xml>
 <http://data.iers.org/products/13/1388/output/116593/finals2000A.daily.xml>

The first file above contain all data for IAU1980 you need. They are
used for legacy Earth frames. The second file is useful if you use more
modern Earth frames (ITRF2008 or thigs like that). So you need both
files if you use both legacy and modern Earth frames.

The drawback of this simple approach is that Orekit will open and parse
a huge xml file that contains much more data than it really needs.

You will have to replace this file from time to time as IERS adds new
data at its end regularly.


> 
> Would the same answers apply for "EOP C01 IAU1980" file?

Orekit does not read EOP C01 files yet (we did not check the format,
it's certainly easy but no one asked for it up to now).

> 
> Are there other files that should be augmented or replaced?

You should take care of the UTC-TAI.history file. This file must be
updated each time a new leap second is about to be introduced. Beware
that there was a leap second introduced at the end of June 2012, so you
really need an up to date file.

> 
> What we're using Orekit for is propagation of TLE data. If there are
> particularly important data files in the orekit-data.zip file related to
> TLE processing, which ones are they?

TLE data processing only needs precession-nutation without EOP
correction so it does not rely on specific data. EOP data is needed when
you use other frames (like TOD with EOP corrections or Earth frames).

Hope this helps,
Luc

> 
> Thanks,
> 
> Craig Ward
>