Re: [Orekit Developers] FieldOfView Detector

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

On 01/18/2016 09:27 AM, Luc Maisonobe wrote:
> Le 18/01/2016 15:16, Luc Maisonobe a écrit :
>> Hi Evan,
>>
>> Le 15/01/2016 09:25, Luc Maisonobe a écrit :
>>> Le 14/01/2016 22:11, Evan Ward a écrit :
>>>> Hi Luc,
>>> Hi Evan,
>>>
>>>> I noticed your recent work on the new field of view classes. I think
>>>> these are a great addition. Would it be possible to model an antenna
>>>> attached to a ground station? I think the current implementation of
>>>> FieldOfView requires a spacecraft state.
>>> You caught me red handed!
>>>
>>> I am also not really comfortable with the spacecraft state in the
>>> offsetFromBoundary method. It induces a dependency that is not
>>> right. It is currently used to convert the input position into
>>> a line of sigth, and this computation should better be performed
>>> at call site, not within the method.
>>>
>>> I'll fix this in a few minutes.
>> I think I will reintroduce a method dedicated to the case the Field Of
>> View is spacecraft centered. It will be something like:
>>
>>  List<GeodeticPoint> getFootprint(SpacecraftState state,
>>                                   OneAxisEllipsoid body);
>>
>> I think it will be better here than for example in
>> FootPrintOverlapDetector because there is no predefined geographic zone
>> here and the method is expected to be called typically from a
>> StepHandler throughout propagation.
>>
>> Do you agree with this new method?
> Also if we add this method, do you think FieldOfView should remain in
> the events package? Perhaps it should be moved to utils (but utils
> is already quite crowded an unstructured).
>
> best regards,
> Luc

I presume the getFootprint method would project a region of the
satellite's celestial sphere to the Earth and then return a set of
points along that boundary. I think it would be a very useful method to
have and I can see the logic in keeping it where it is. As for the
parameters, if you're using the ellipsoidal Earth assumption to make the
computation quicker then I think OneAxisEllipsoid is the right type. On
the other hand if the algorithm is using ray tracing or some similar
algorithm then I think using a BodyShape would add flexibility so users
could include the effects of terrain by providing and terrain based
BodyShape.

Best Regards,
Evan

>
>> best regards,
>> Luc
>>
>>> I did not foresee using this for ground stations! Once the method
>>> signature is fixed, it may be used this way too. Would you mind
>>> updating the javadoc to explain this other use? I don't know
>>> either if the name FieldOfView is well suited in this case, so maybe it
>>> should be renamed at the same time.
>>>
>>> best regards,
>>> Luc
>>>
>>>> Best Regards,
>>>> Evan
>>>>