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Overlay to measure height and length of promances and filaments?

8 replies to this topic

#1 Barnstorm

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Posted 29 November 2021 - 12:52 PM

Has anyone created an overlay to measure height and length of promances and filaments on images?

This would save me the work of putting a caliper on the screen and hoping I get the math right.

#2 Cotts

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Posted 29 November 2021 - 12:59 PM

You may wish to look into "AstroimageJ" software.  Pixel-level analysis of images can easily be done with this software. i.e one end of the prominence is at pixel (x1,y1) and the other end of the prominence is at pixel (x2,y2).  Pythagoras finds the distance between the two points. Combined with the knowledge of the operating focal length of your imaging system (image or plate scale) and the pixel size of your camera you will derive the length of the prominence in arc seconds.

I measure double star separations the same way to 0.1" accuracy.

Dave

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#3 MalVeauX

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Posted 29 November 2021 - 01:29 PM

Has anyone created an overlay to measure height and length of promances and filaments on images?

This would save me the work of putting a caliper on the screen and hoping I get the math right.

The overlay will only work if your image scale matches it. So you'll have to get the math right first anyways.

A simple way to do this is to simply get your image scale, then solar disc image scale and then you know the distance per pixel essentially. Then you can just pixel measure and get a fairly accurate measurement to the pixel's scale in terms of resolution of the measurement.

The math stuff:

Image scale ("/pixel) = Pixel Size (um) / Effective Focal Length (mm) * 206.265

Solar disc scale in pixels based on your image scale = 1800 / (your image scale result)

You now have your solar disc diameter in pixels relative to your image scale.

The solar disc is 1,390,473 kilometers in diameter.

So your scale is then 1,390,473 / (your solar scale value) and you get the distance in your solar scale per pixel in kilometers.

+++++++++++++++++++++++++++++++

Example, let's my typical setup:

150mm F8 (1200mm focal length) refractor

IMX290 sensor (2.9um pixels)

My image scale:

(2.9um / 1200mm) * 206.655 = 0.5"/pixel

My Solar Scale:

1800 / 0.5"/pixel = 3600 pixel solar disc at my image scale

1,390,473 km solar diameter / 3600 pixels = 386.24km per pixel for measuring features

(disclosure, I rounded a bit for simplicity for anyone checking the math)

I can now just drag a box over the prom or any feature in your image and do a pixel count and it will be pretty accurate, without having to do an overlay.

I also have an excel calculator written to do this for you. Just input your focal length & pixel size on your sensor and hit enter. The calcs are done on the right.

Very best,

Edited by MalVeauX, 29 November 2021 - 01:42 PM.

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#4 peterm

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Posted 29 November 2021 - 03:51 PM

This overlay may give some idea and works very well with GIMP and Photoshop.

https://www.cloudyni...r#entry10711138

I had a friend translate it to English per attached.

Attached Files

Edited by peterm, 29 November 2021 - 03:52 PM.

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#5 chemman

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Posted 29 November 2021 - 05:49 PM

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#6 philmor56

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Posted 29 November 2021 - 05:54 PM

This is a simple JAVA script that does overlays and will also insert an image of the earth to scale.

It might be similar to the one Chuck just recommended.

http://www-old.astro...iciels/lusol3d/

Make sure you install JAVA first.

Cheers

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#7 Barnstorm

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Posted 29 November 2021 - 09:21 PM

perfect!!! thanks!

#8 Cotts

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Posted 30 November 2021 - 12:31 AM

Has anyone created an overlay to measure height and length of promances and filaments on images?

This would save me the work of putting a caliper on the screen and hoping I get the math right.

Addendum:  I see you are using a C11.  If you plan to use the focal length of the scope in your calculations be aware that it is definitely not the stated f/11 x aperture.   The focal length of an SCT changes dramatically as you change the focus.  The actual focal length varies +/- 10% or even more.

To get the actual focal length (image scale) you would have to  set up your camera imaging train and take a picture of the night sky.  Then upload it to astrometry.net for plate solving.

Dave

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#9 Barnstorm

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Posted 30 November 2021 - 08:43 AM

Addendum:  I see you are using a C11.  If you plan to use the focal length of the scope in your calculations be aware that it is definitely not the stated f/11 x aperture.   The focal length of an SCT changes dramatically as you change the focus.  The actual focal length varies +/- 10% or even more.

To get the actual focal length (image scale) you would have to  set up your camera imaging train and take a picture of the night sky.  Then upload it to astrometry.net for plate solving.

Dave

Thanks!

FYI, I don't use the C11 for solar work. Just the Solar Max 60 and 90.

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