equatorial vs planetographic frames

[cpotting]

Hello everyone,

I am hoping that someone can help me understand the difference between equatorial and planetographic frames of reference.

I was under the impression that the equatorial frame of reference would have an X-Z plane that runs through the equator of the reference object (hence "equatorial") and that the Y axis would then run through the object's poles of rotation. I never understood what the planetographic frame of reference was supposed to be.

With that in mind, I was surprised when

Code: Select all

earth_frame_equatorial = celestia:newframe("equatorial", earth)
above_pole_position = celestia:newposition(0, 100000 / KM_PER_MLY, 0)
earth_above_pole_position_universal = earth_frame_equatorial:from(above_pole_position)

did not create a position over earth's north pole, but rather over the arctic circle - appearently aligned with the earth's orbital plane. I was further suprised when

Code: Select all

earth_frame_planetographic = celestia:newframe("planetographic", earth)
above_pole_position = celestia:newposition(0, 100000 / KM_PER_MLY, 0)
earth_above_pole_position_universal = earth_frame_planetographic:from(above_pole_position)

did create a position over the north pole. Now I don't know what the equatorial frame of reference is supposed to be.

Any help would be appreciated.

[Harry]

I am hoping that someone can help me understand the difference between equatorial and planetographic frames of reference.

Apparently there is no special code in frame.cpp to handle "Equatorial", which makes it the same as the "Ecliptical" frame. Not sure about "observer" (a.k.a. as ObserverLocal) either. Maybe Chris can explain what their purpose is...

Harald

[chris]

Oops. Looks like an omission in the scripting system that needs to be corrected. Then, your code should work as you expect it to.

--Chris

[cpotting]

Oops. Looks like an omission in the scripting system that needs to be corrected. Then, your code should work as you expect it to.

--Chris

Well, I am happy to find out that my interpretation of "equatorial" was correct... but that still leaves me wondering what "planetographic" is supposed to be.

[chris]

Oops. Looks like an omission in the scripting system that needs to be corrected. Then, your code should work as you expect it to.

--Chris

Well, I am happy to find out that my interpretation of "equatorial" was correct... but that still leaves me wondering what "planetographic" is supposed to be.

The planetographic coordinate system accounts for planet rotation, and equatorial does not. An object at a constant position in the planetographic system will remain fixed with respect to the surface of the planet. Perhaps I could have used better terminology.

--Chris

[cpotting]

The planetographic coordinate system accounts for planet rotation, and equatorial does not. An object at a constant position in the planetographic system will remain fixed with respect to the surface of the planet. Perhaps I could have used better terminology.

--Chris

No, I think the terminology is fine - now that I know what it is. I can't think of a term that would work better. Thanks guys, this helps a lot.