Rotation angle in the Ocular Plugin doesn't comply with the standard.

[Nicolas T]

Hi

The rotation angle calculated in the Ocular plugin is calculated west of north and increasing the angle make the field of view turn clokwise.

This is not standard because the angle must be calculated east of north and increasing the angle should result in a counterclockwise rotation.

This astronomical position angle standard is used in most astronomical applications and is define by the International Astronomical Union (see here: https://en.wikipedia.org/wiki/Position_angle)

NINA, for example, changed the way it calculates angles in its latest version (3.0) to comply with this standard. See the release note here: https://f002.backblazeb2.com/file/ninasetup/Releases/3.0.0.9001/RELEASE_NOTES.html

Here is an exemple in stellarium:

https://1drv.ms/i/s!AgPwp5gOmTQUgfhmaimSF9EP2mLkqg?e=EodRRw

For this field of view stellarium display an angle of 71°

But the expected rotation angle of this field of view is 289° east of north:

https://1drv.ms/i/s!AgPwp5gOmTQUgfcSzu-1bQIdyKRvOA?e=YZdhJE

Nicolas

[Alexander V. Wolf]

Hi!

пт, 19 апр. 2024 г. в 17:31, Nicolas T <nicolas...@gmail.com>:

The rotation angle calculated in the Ocular plugin is calculated west of north and increasing the angle make the field of view turn clokwise.

Yes, this is correct behavior.

 

This is not standard because the angle must be calculated east of north and increasing the angle should result in a counterclockwise rotation.

Why? All buttons for rotation of CCD frame has tooltips with notifications for clockwise or counterclockwise rotation behavior.

 

This astronomical position angle standard is used in most astronomical applications and is define by the International Astronomical Union (see here: https://en.wikipedia.org/wiki/Position_angle)

This is nice, but the position angle is not equals to the rotation angle.

 

NINA, for example, changed the way it calculates angles in its latest version (3.0) to comply with this standard. See the release note here: https://f002.backblazeb2.com/file/ninasetup/Releases/3.0.0.9001/RELEASE_NOTES.html

Here is an exemple in stellarium:

https://1drv.ms/i/s!AgPwp5gOmTQUgfhmaimSF9EP2mLkqg?e=EodRRw

For this field of view stellarium display an angle of 71°

But the expected rotation angle of this field of view is 289° east of north:

https://1drv.ms/i/s!AgPwp5gOmTQUgfcSzu-1bQIdyKRvOA?e=YZdhJE

Again, this is different angles.

--

With best regards, Alexander

[Nicolas T]

Hello Alexandre and thank you for your response.

Can you describe the difference between position angle and rotation angle as I don't see it?  What does the rotation angle mean? 

The position angle is meant to describe the angle of anything in the sky (in an absolute way).  I think this applies perfectly to this scenario.

This way we could use stellarium to frame an object and just use the angle in any acquisition software.

Nicolas

[Alexander V. Wolf]

пт, 19 апр. 2024 г. в 18:12, Nicolas T <nicolas...@gmail.com>:

Can you describe the difference between position angle and rotation angle as I don't see it?  What does the rotation angle mean? 

Rotation angle is self-explanatory angle, and he says to users how the CCD is attached to the telescope. For example, in horizontal mount (or alt-azimuthal mount) you can rotate the telescope with CCD around a vertical axis and rotation angle will have the same value, but positional angle will always change.

 

The position angle is meant to describe the angle of anything in the sky (in an absolute way).  I think this applies perfectly to this scenario.

No. Position angle is applicable for setups (Telescope+CCD) on equatorial mounts for describing how the picture oriented in equatorial coordinates. This angle can't give information about physical orientation of CCD onto telescope for you.

 

[Nicolas T]

Ok, thanks to you I realize I forgot about a very important setting: the Equatorial mount check in the Telescopes Tab.

When this parameter is not checked, the angle displayed is relative to the azimuthal grid, 0° being the CCD parallel to the ground. In this situation, when you move the scope with your Alt-azimuth mount, the angle of rotation remains unchanged but the position of the image on the equatorial grid changes. This angle is therefore certainly not the same as the position angle. I see this now.

But when the "Equatorial mount" parameter is checked, then the displayed angle is relative to the equatorial coordinate grid and is not directly linked to the orientation of the CCD with respect to the telescope.

Isn't this angle then the same thing as the position angle?

[Nicolas T]

Ok, thanks to you I realized that I had forgotten the "Equatorial mount" parameter in the "Telescopes" tab.

When this parameter is unchecked, then the angle displayed is relative to the Azimuthal grid (0° being the CCD parallel to the ground). In this configuration, when you move your Alt-Az mount, the angle displayed will not change but the orientation of the picture in the equatorial grid will change. This angle is therefore not the same thing at all as the position angle. I realize this now.


But when the "Equatorial mount" parameter is checked, then the displayed angle is relative to the equatorial coordinate grid and is no directly linked to the orientation of the CCD with respect to the telescope. This angle only defines how the picture is oriented in the equtorial coordinates.
In this configuration (Equatorial Mount) isn't this angle equivalent to the position angle?

[Alexander V. Wolf]

Hi!

пт, 19 апр. 2024 г. в 21:46, Nicolas T <nicolas...@gmail.com>:

Ok, thanks to you I realized that I had forgotten the "Equatorial mount" parameter in the "Telescopes" tab.

When this parameter is unchecked, then the angle displayed is relative to the Azimuthal grid (0° being the CCD parallel to the ground). In this configuration, when you move your Alt-Az mount, the angle displayed will not change but the orientation of the picture in the equatorial grid will change. This angle is therefore not the same thing at all as the position angle. I realize this now.

But when the "Equatorial mount" parameter is checked, then the displayed angle is relative to the equatorial coordinate grid and is no directly linked to the orientation of the CCD with respect to the telescope. This angle only defines how the picture is oriented in the equtorial coordinates.

The orientation of the camera relative to the telescope does not depend on the type of mount.