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Catalog of all Astrobin Images of the Day

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#1 astro_alex80

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Posted 05 December 2021 - 07:08 AM

Hi community,

 

@Admins:

Decided to put this in a new topic as subject is going further than my initial topic around coordinate calculation.

If you feel its better to integrate my early topics please do so.

 

 

After successfully displaying my own images, I fetched via the RestAPI the center coordinates, width, height, pixel scale and rotation of all Astrobin Images of the Day (IOTD) which are having a valid plate solving solution.

 

Basic idea is to put a catalog of all Astrobin IOTD together showing the areas most captured/awarded and providing some image details such as date, image rig used, etc.

 

Salvatore, the owner of Astrobin, is well aware of the project.

Here the first preview of the generated Cartes du Ciel catalog using the RA, DEC center coordinates and image circle.

Chart_1.jpg

 

 

Thanks to support in an early topic about coordinate calculation https://www.cloudyni...e-calculations/ I also managed to draw rectangles of the images instead only circles to create a more realistic appearance.

(for testing it's only a selection of IOTDs)

Chart_2_rect.jpg

 

 

However, as closer it gets to the pole or for widefield images the rectangles start looking strange, which I understand as I try to display a simple 2D rectangle on a sphere.

Here a preview of what I mean:

Chart_3_nearPole.jpg

 

 

I am doing the calculations in a script for each image corner as following:

// corner down left
$nX_Old = RA Center - image width in decimal degrees / 2
$nX_Rot = RA Center in decimal degrees as image center = rotation center

$nY_Old = DEC Center - image height in decimal degrees / 2
$nY_Rot = DEC Center in decimal degrees as image center = rotation center

$angle = rotation angle converted in Radiant

// for the new X-Coordinate
$nX_New = ($nX_Old - $nX_Rot) * cos($angle) - ($nY_Old - $nY_Rot) * sin($angle) ;

if ($nX_New < 0) $nX_New = 360 - $nX_New;
if ($nX_New > 360) $nX_New = $nX_New - 360;


// for the new Y-Coordinate
$nY_New = ($nX_Old - $nX_Rot) * sin($angle) + ($nY_Old - $nY_Rot) * cos($angle) ;

For the other corners I accordingly add half of the image width or half of the image height or I subtract it to get the orginal (old) corner coordinates of a not rotated rectangle.

 

Being honest, I have reached limits of my capabilities here, the whole topic about coordinate transformation is far too long ago for me and especially transforming them to be correctly displayed on a sphere, I am out unfortunately.

 

I would be extremely happy someone could give a helping hand with the formulas supporting the creation of a correctly appearing catalogue or at least point me to a solution.

No ultimate precision is required here as the catalog is for information purpose only.

 

 

Here are some data, who wants to give it a try calculating (Epoch 2000):

RA: 22.00600 DEC: -73.3340 Width: 1.023120 Height: 0.682080 Angle: 177.8280

RA: 106.4650 DEC: 51.41700 Width: 8.990975 Height: 13.48646 Angle: 358.7710

RA: 84.61900 DEC: 28.18700 Width: 6.362222 Height: 4.214972 Angle: 177.0880

 

 

Kind regards,

Alex


Edited by astro_alex80, 05 December 2021 - 07:11 AM.

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#2 alphatripleplus

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Posted 05 December 2021 - 07:49 AM

Sounds like a project that would be of interest to many that enjoy looking at APODs.



#3 lambermo

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Posted 06 December 2021 - 02:30 PM

Confused. What is the question ? the big rectangle on the left side looks fine to me, it is as how I'd expect it to be.



#4 Patrick Chevalley

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Posted 06 December 2021 - 03:35 PM

Nice project, congratulation!

 

The RA part of the rectangle size need to be divided by COS(DEC). This way the rectangle must be draw with the right proportion.



#5 astro_alex80

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Posted 08 December 2021 - 12:35 AM

Thanks for your feedback.

Managed a better representation of the FOV, in fact by including cos of the DEC axis you suggested Patrick,

see the screenshot below.

 

However still having issues with a few widefield images in pole region, like the one of 02nd Nov 21

https://www.astrobin.com/8zun6y/

 

The data are

RA Center: 331.4970 DEC Center: 74.02800 Radius: 22.51700 Width: 39.85144 Height: 20.97344 Angle: 85.75700

 

 

Is there an option to include description / object data to such nebulae outlines as well ?

Otherwise I put object data and description to another separate catalog.

 

 

Orion_Region.png


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#6 R Botero

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Posted 08 December 2021 - 05:14 AM

Great project 👍

Roberto

#7 astro_alex80

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Posted 08 December 2021 - 05:54 AM

Thanks Roberto, once remaining small issues solved and double checked I will make the catalog available to download.


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