Discrepancies at Celestia general projection

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Discrepancies at Celestia general projection

Post #1by Alejandro » 13.02.2019, 16:39

Hi everyone, it is nice to be here again!

I write to all of you because I think there is something wrong regarding Celestia projections that may need to be corrected.
I notice some discrepancies beteween original planets views in relation with that same maps projected by Celestia.

In the example attached (animated GIF), the earth as seen from space (Epic Polichromatic Camera) and Celestia Earth projection the same day: notice the size of Africa and the rest of the land. I also imagine that this may affect the correct position of the terminator over the map. This also happens with wichever map you use.


Does anyone know how to fix this?
Thank you!

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Post #2by LukeCEL » 14.02.2019, 03:20

I think what's going on is that the distances in the two images are different!

The satellite that EPIC is on, Deep Space Climate Observatory, is about 1.5 million km away from Earth (according to Wikipedia). At that distance, the Earth actually appears pretty small, so the EPIC picture is zoomed in a lot. On the other hand, I'm not sure what distance you took your Celestia screenshot at, but I'm assuming it's a lot closer than that. Since the Earth is a lot closer, differences in distance matter a lot more. Here, Africa looks a lot bigger because it sticks out relative to the rest of the world, therefore it looks bigger.

I tried to simulate this with two Cel URLs that you can click on. Here's the DSCOVR view: cel://SyncOrbit/Sol:Earth/2019-02-13T13:03:00.258 ... 1&rf=3446679&lm=0&tsrc=0&ver=3

and here's a view from about 25,000 km: cel://SyncOrbit/Sol:Earth/2019-02-13T13:03:00.258 ... 1&rf=3446679&lm=0&tsrc=0&ver=3

P.S. Fun fact, the same effect seems to occur when people take selfies, apparently.

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Post #3by Alejandro » 14.02.2019, 18:17

Thank you, LukeCel, for your concern and for your answer.
I think you are right about it. I also make another attemp taking into account the distance factor.
I use one pic of the Earth as seen from one of the Apollo 17 missions at a distance of 112.831 km and make the comparison: the result seems to be the same in both cases:


So we can continue exploring the Solar System without fear!

Thank again!

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