Placing a mark at an exact coordinate

Image processing, astrometry, photometry, etc.
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Rudi
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Joined: 08 Jan 2019, 04:47

Placing a mark at an exact coordinate

Post by Rudi » 28 Nov 2022, 13:57

Is it possible to place a cross or another mark at an exact coordinate in a platesolved image?
It can me bard to fiddle arround with the mouse and this method isn't very precice either.
/Rudi

AlessandroMaitan
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Joined: 09 May 2019, 08:02

Re: Placing a mark at an exact coordinate

Post by AlessandroMaitan » 29 Nov 2022, 08:16

As far as I know you can only position an annotation on pixel coordinates.

Alessandro

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Rudi
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Re: Placing a mark at an exact coordinate

Post by Rudi » 29 Nov 2022, 09:04

Exactly - hence my question ;-)


I found a workarround yesterday evening. If I zoom an extremely ammount in, such that pixels in the image is eg 20x20 pixels on the screen, I can identify the pixel that closest match the coordinate by fiddeling the cursor arround.
But this is cumbersome, if you need to place many marks.
/Rudi

fabdev
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Joined: 03 Dec 2018, 21:43

Re: Placing a mark at an exact coordinate

Post by fabdev » 29 Nov 2022, 13:40

Hi, it can be done with the menu command: Image / Select / Coordinates. The shortcut is CTRL + ALT + P.
Another solution could be a script which asks the coordinates then transform them with the command Image.XY(ra,dec)

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Rudi
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Re: Placing a mark at an exact coordinate

Post by Rudi » 30 Nov 2022, 04:31

Thanks Fabio, that worked great.
Is it possible then to place a Annotation at the mark precicely then?
/Rudi

fabdev
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Joined: 03 Dec 2018, 21:43

Re: Placing a mark at an exact coordinate

Post by fabdev » 01 Dec 2022, 02:36

Hello, no, but after the annotation is moved with the mouse, it can be moved precisely with the keyboard with CTRL + arrows.

Actually if the point is removed and it's replaced with a star selection, then snapping is possible with the experimental shortcut SHIFT + S (with the annotation active, and annotations window opened). Ideally the procedure is to select first all stellar objects, then open the Stars Window to select the desired star, then SHIFT + S to snap to the selected star, so:

1) Select some stars in the image.
2) Open the Annotation Window and click "New".
3) Select the star in the Stars Window.
4) Press SHIFT + S.

Greetings, Fabio.

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Rudi
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Re: Placing a mark at an exact coordinate

Post by Rudi » 01 Dec 2022, 08:22

fabdev wrote:
01 Dec 2022, 02:36
Hello, no, but after the annotation is moved with the mouse, it can be moved precisely with the keyboard with CTRL + arrows.

Actually if the point is removed and it's replaced with a star selection, then snapping is possible with the experimental shortcut SHIFT + S (with the annotation active, and annotations window opened). Ideally the procedure is to select first all stellar objects, then open the Stars Window to select the desired star, then SHIFT + S to snap to the selected star, so:

1) Select some stars in the image.
2) Open the Annotation Window and click "New".
3) Select the star in the Stars Window.
4) Press SHIFT + S.

Greetings, Fabio.
Thanks - that also worked. Not sure if I can remember this next time though ;-)
And still, it wouldn't work if you have to place an annotation at a precise location where there's no star.

It would be very convenient, if the Coordinates section of the Annotations dialog had a ra/dec option.

Btw - "Image -> Select Coordinates" isn't enabled unless you "Plate solve" the image. If "Platesolve immediate", "Select Coordinates" remain disabled in the menu.
/Rudi

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