Re: [Orekit Users] geoid undulation

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

Le 25/02/2015 15:25, Odenstein Manfred a écrit :
> Hi Luc,

Hi Odi,

Here are some new information about this topic.
Evan Ward just added an implementation of a geoid that can be
computed directly from any normalized gravity field and a
reference ellipsoid.  It can compute undulation and also
performs direct transforms like computing latitude/longitude/orthometric
altitude and line/geoid intersection.

The corresponding classes and interfaces are in the models.earth package.

best regards,
Luc


> 
> thank you for the information, I’ve another question regarding geoid undulation, please correct me if I’m wrong:
> 
> In the orekit WMM implementation (GeoMagneticField), it is stated that the given hight in calculateField is "the altitude in kilometers above mean sea level“, but the WMM.COF file with the mentioned NGA WMM_SubLibrary.c only supports hight above ellipsoid (wgs84), is there documentation error ? The NOAA software accepts both ellipsoid hight and MSL by doing an undulation calculation with EGM96 15min grid interpolation, but I miss this in the orekit implementation.
> 
> In the orekit WMM.COF file format there exists both min. and max. altitude, from where are these values from  ?
> 
> thank you and best regards
> odi
> 
>> Am 23.02.2015 um 09:20 schrieb Luc Maisonobe <Luc.Maisonobe@c-s.fr>:
>>
>> Hi Odi,
>>
>> Le 22/02/2015 16:30, Odenstein Manfred a écrit :
>>> Hi, sorry, I'm not the math expert, but I'm using orekit for the
>>> magnetic field calculations, as I now need also some gravity
>>> calculations, especially undulation, I've found the implementation of
>>> a model reader for EGM96, EGM2008, etc but found no method which
>>> takes lat/lon and date to retrieve the information. I'm just oversee
>>> something or is nothing there ?
>>
>> You did not oversee anything. There are no undulation computation yet in
>> Orekit. We will probably add one in the future, as it is important for
>> example for some Digital Elevation Models that are referenced to geoid
>> and not to ellipsoid.
>>
>> The model readers you found are dedicated to look at the gravity field
>> from a dynamical point of view, not from the undulation perspective.
>> This means they are used to compute at any point in space the gravity
>> vector. Undulation are more seen as an iso-surface on the combination of
>> this gravity field plus some other parts like inertial forces due
>> to Earth rotation. So they share some data, but we did not implement yet
>> the second perspective.
>>
>> Of course, contributions are welcome so if you decided to come up with
>> the missing parts, we will look at how to include it in Orekit.
>>
>>>
>>> any help would be appreciated thank you and best regards odi
>>>
>>
>> best regards,
>> Luc
>>
>>
>