POV-Ray : Newsgroups : povray.advanced-users : Calculating planet positions Server Time
31 Oct 2024 19:17:53 EDT (-0400)
  Calculating planet positions (Message 16 to 25 of 25)  
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From: Mike Horvath
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 02:52:12
Message: <5bab2c9c@news.povray.org>
Oops, here are the files once again. (Ignore the previous ones.)


Mike


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Attachments:
Download 'celestia_screenshot_01.png' (130 KB) Download 'do_not_delete.pov.txt' (5 KB) Download '2k_earth_daymap.jpg' (453 KB)

Preview of image 'celestia_screenshot_01.png'
celestia_screenshot_01.png

Preview of image '2k_earth_daymap.jpg'
2k_earth_daymap.jpg


 

From: Le Forgeron
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 12:40:01
Message: <5babb661@news.povray.org>
Le 26/09/2018 à 08:52, Mike Horvath a écrit :
> Oops, here are the files once again. (Ignore the previous ones.)
> 
> 
> Mike

I added the tilting axis (yellow) of the planet and the relevant
transformation.

I do not touch obliquity.

#declare TILT_AXIS = vrotate( x, (90+alpha_0)*z );
/* same as
#declare TILT_AXIS = vrotate( y, alpha_0*z );
*/
#include "transforms.inc"

#declare sphere_trans = transform
{
	rotate z * W
  Axis_Rotate_Trans( TILT_AXIS, 90-delta_0 )
	//rotate x * (90-delta_0)
	//rotate z * (90+alpha_0)
	rotate x * -obliquity
}


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Attachments:
Download 'step.png' (163 KB) Download 'step.pov.txt' (4 KB)

Preview of image 'step.png'
step.png

From: Mike Horvath
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 13:44:58
Message: <5babc59a$1@news.povray.org>
Thanks again for the help!

A couple of comments:

1. What is the significance of the long yellow cylinder?

2. The render of "step.pov" you posted still does not look like the 
Celestia screenshot. The Celestia screenshot in my last post is what the 
scene *should* look like, and the scene is off by quite a bit. I'm not 
sure what's wrong, either.


Mike


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From: clipka
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 13:47:15
Message: <5babc623$1@news.povray.org>
Am 26.09.2018 um 19:45 schrieb Mike Horvath:

> 1. What is the significance of the long yellow cylinder?

Looks like direction to the sun.


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From: Mike Horvath
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 14:15:34
Message: <5babccc6$1@news.povray.org>
On 9/26/2018 1:47 PM, clipka wrote:
> Am 26.09.2018 um 19:45 schrieb Mike Horvath:
> 
>> 1. What is the significance of the long yellow cylinder?
> 
> Looks like direction to the sun.
> 

No, on Julian Date 2458383.5 the Sun should be directly along the -x axis.


Mike


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From: clipka
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 14:31:47
Message: <5babd093$1@news.povray.org>
Am 26.09.2018 um 20:15 schrieb Mike Horvath:
> On 9/26/2018 1:47 PM, clipka wrote:
>> Am 26.09.2018 um 19:45 schrieb Mike Horvath:
>>
>>> 1. What is the significance of the long yellow cylinder?
>>
>> Looks like direction to the sun.
>>
> 
> No, on Julian Date 2458383.5 the Sun should be directly along the -x axis.

It does match the shadow of the pole pole though (pun intended).


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From: Le Forgeron
Subject: Re: Calculating planet rotations
Date: 26 Sep 2018 16:26:47
Message: <5babeb87$1@news.povray.org>
Le 26/09/2018 à 19:45, Mike Horvath a écrit :
> Thanks again for the help!
> 
> A couple of comments:
> 
> 1. What is the significance of the long yellow cylinder?

It is the axis around which the planet get rotated by 90-delta degree,
to place its pole axis in space.

> 
> 2. The render of "step.pov" you posted still does not look like the
> Celestia screenshot. The Celestia screenshot in my last post is what the
> scene *should* look like, and the scene is off by quite a bit. I'm not
> sure what's wrong, either.

I'm still not sure about your ecliptic correction, can you try to see
what happen when you remove it ?
Also, check your camera parameter, there was a bit of comments and I
might have touched it.

Loonking at the French wikipedia for equatorial coordinate system,

https://fr.wikipedia.org/wiki/Syst%C3%A8me_de_coordonn%C3%A9es_%C3%A9quatoriales

there is a note about converting alpha to latitude/time.

+alpha is to the east.

English version has even an animation:

https://en.wikipedia.org/wiki/Equatorial_coordinate_system

Is the mismatch about the pole ?
Or the placement of continents ?

I'm not sure about the axis of obliquity, especially after the transform
of alpha & delta.



> 
> 
> Mike


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From: Mike Horvath
Subject: Re: Calculating planet rotations
Date: 27 Sep 2018 18:19:24
Message: <5bad576c@news.povray.org>
On 9/26/2018 4:26 PM, Le_Forgeron wrote:
> Le 26/09/2018 à 19:45, Mike Horvath a écrit :
>> Thanks again for the help!
>>
>> A couple of comments:
>>
>> 1. What is the significance of the long yellow cylinder?
> 
> It is the axis around which the planet get rotated by 90-delta degree,
> to place its pole axis in space.
> 

Okay thanks.

>>
>> 2. The render of "step.pov" you posted still does not look like the
>> Celestia screenshot. The Celestia screenshot in my last post is what the
>> scene *should* look like, and the scene is off by quite a bit. I'm not
>> sure what's wrong, either.
> 
> I'm still not sure about your ecliptic correction, can you try to see
> what happen when you remove it ?


Conversions to/from ecliptic coordinates and equatorial coordinates 
(ICRF frame) are described here:

https://en.wikipedia.org/wiki/Ecliptic_coordinate_system#Conversion_between_celestial_coordinate_systems

as well as in step #6 here:

https://ssd.jpl.nasa.gov/txt/aprx_pos_planets.pdf

It seems to be a simple rotation around the x axis.


 > Also, check your camera parameter, there was a bit of comments and I
 > might have touched it.
 >

The camera also seems fine, since the red, green and blue poles are all 
pointing in the correct directions.



> Loonking at the French wikipedia for equatorial coordinate system,
> 
> https://fr.wikipedia.org/wiki/Syst%C3%A8me_de_coordonn%C3%A9es_%C3%A9quatoriales
> 
> there is a note about converting alpha to latitude/time.
> 
> +alpha is to the east.
> 
> English version has even an animation:
> 
> https://en.wikipedia.org/wiki/Equatorial_coordinate_system
> 
> Is the mismatch about the pole ?
> Or the placement of continents ?
> 
> I'm not sure about the axis of obliquity, especially after the transform
> of alpha & delta.

I've attached four comparison views of the POV-Ray output versus 
Celestia. Maybe they will illuminate which rotations are being done 
incorrectly?

The dark red, green and blue cylinders represent the ecliptic frame 
axes. The bright red, green and blue cylinders represent the body frame 
axes. If you ignore the axes, some of the renders look "close" to correct.


Mike


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Attachments:
Download 'celestia_earth_01.jpg' (217 KB) Download 'celestia_mars_01.jpg' (245 KB) Download 'celestia_saturn_01.jpg' (309 KB) Download 'celestia_uranus_01.jpg' (240 KB)

Preview of image 'celestia_earth_01.jpg'
celestia_earth_01.jpg

Preview of image 'celestia_mars_01.jpg'
celestia_mars_01.jpg

Preview of image 'celestia_saturn_01.jpg'
celestia_saturn_01.jpg

Preview of image 'celestia_uranus_01.jpg'
celestia_uranus_01.jpg


 

From: Mike Horvath
Subject: Re: Calculating planet rotations
Date: 27 Sep 2018 22:45:55
Message: <5bad95e3@news.povray.org>
Neptune also seems "close" in the same way.


Mike


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Attachments:
Download 'celestia_neptune_01.jpg' (225 KB)

Preview of image 'celestia_neptune_01.jpg'
celestia_neptune_01.jpg


 

From: Mike Horvath
Subject: Re: Calculating planet rotations
Date: 28 Sep 2018 00:46:40
Message: <5badb230@news.povray.org>
On 9/27/2018 10:46 PM, Mike Horvath wrote:
> Neptune also seems "close" in the same way.
> 
> 
> Mike


Here's a better view of Neptune if that helps.


Mike


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Attachments:
Download 'celestia_neptune_01.jpg' (238 KB)

Preview of image 'celestia_neptune_01.jpg'
celestia_neptune_01.jpg


 

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