Definition of orientation

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masaki otsuki

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Jul 31, 2021, 1:20:25 AM7/31/21
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Hello everyone.
I'd like to know the definition of orientation in the result.
Both of  following two results are about Polaris. Second one is taken after rotating the camera about 90 degrees.

The orientation of first one is "Up is 259 degrees E of N", and second one is "Up is 68.3 degrees E of N".
I'd like to know which angle each value means.

The north celestial pole is at almost same direction from the center of the image in both of images. So I think they should be almost same values, but completely  different.
Is there any document that explain about it?



Dustin Lang

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Jul 31, 2021, 9:54:53 AM7/31/21
to masaki otsuki, astrometry
The orientation is based on the "CD matrix" elements in the WCS solution.  WCS has a tangent point and a matrix that says how much RA and Dec increase with X and Y.

You should set the "CRPIX in center" option to get more understandable orientation values when your image contains the pole.

cheers,
--dustin



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masaki otsuki

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Jul 31, 2021, 6:58:12 PM7/31/21
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Thank you for the advice. I tried it and it works on nova astrometry!. 

Next, I set the option to solve-field that runs on my local PC with the same image, but it gave me different value from nova. 
Have you ever seen such phenomenon?
 
2021年7月31日土曜日 22:54:53 UTC+9 dstn...@gmail.com:

Dustin Lang

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Jul 31, 2021, 7:06:45 PM7/31/21
to masaki otsuki, astrometry
You have
 solve-field --crpix-center
?

The index files will be different, so I would expect possibly slightly different values.  What values are you getting?

cheers,
--dustin



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masaki otsuki

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Jul 31, 2021, 8:50:24 PM7/31/21
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Yes, I set "--crpix-center" to solve-field. 
The answer of solve-field is 127.777 and the nova is 52.1.

I tried another image that includes pole too, and the answer of solve-field is 154.69, and nova is 78.6 degree E of N.

2021年8月1日日曜日 8:06:45 UTC+9 dstn...@gmail.com:

Dustin Lang

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Jul 31, 2021, 9:29:27 PM7/31/21
to masaki otsuki, astrometry
Are you solving JPEG or FITS images?  There may be a 180 degree or vertical flip difference between nova and solve-field.

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masaki otsuki

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Aug 1, 2021, 5:57:15 PM8/1/21
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I solve JPEG file. How different between nova and solve-field? I flipped vertically and solved with solve-field, it answers negative value of nova.

2021年8月1日日曜日 10:29:27 UTC+9 dstn...@gmail.com:

Dustin Lang

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Aug 1, 2021, 6:15:28 PM8/1/21
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masaki otsuki

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Aug 3, 2021, 9:53:47 AM8/3/21
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Thank you for the link. I understood!.

2021年8月2日月曜日 7:15:28 UTC+9 dstn...@gmail.com:
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