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Stacking data taken from different locations


Pryce

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This might sound stupid and I'm pretty sure it would be fine. 

But I'm imaging from one location tonight and from somewhere else this weekend.

So I'm wondering if it's fine to stack this data or if I'll run into any problems?

Edited by Pryce
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  • Pryce changed the title to Stacking data taken from different locations
3 hours ago, Pryce said:

This might sound stupid and I'm pretty sure it would be fine. 

But I'm imaging from one location tonight and from somewhere else this weekend.

So I'm wondering if it's fine to stack this data or if I'll run into any problems?

Should be OK, and unless you're imaging with a wide angle lens (where field distortion is significant) the orientation/alignment of the images between the 2 nights shouldn't really matter (afterall the stacking software copes with drift resulting from poor polar alignment and meridian flips).

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Even if the camera orientation is not the same, things will work, I find. Even from my own back garden, camera orientation can vary quite a bit, but that doesn't hurt the end result. There may of course be large differences in gradients caused by light pollution, so I generally stack each session in Astro Pixel Processor (APP), and let it compute a weight map as well. I then remove light pollution in APP as well, and later combine the different results, by importing the images with pollution correction and the weight maps in APP, and stacking those (generally very quick because you are combining just a  few "subs".

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5 hours ago, Seelive said:

Should be OK, and unless you're imaging with a wide angle lens (where field distortion is significant) the orientation/alignment of the images between the 2 nights shouldn't really matter (afterall the stacking software copes with drift resulting from poor polar alignment and meridian flips).

Having said that, depending upon the angular orientation and/or field centre of the two sets of images, the final image may require severe cropping so as to just include the common imaged areas. Therefore, if your intended target is a significant proportion of the image size and the orientation/field centre of the 2 sets of images are not similar, it could result in a significant loss of otherwise useful data.

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9 minutes ago, Seelive said:

Having said that, depending upon the angular orientation and/or field centre of the two sets of images, the final image may require severe cropping so as to just include the common imaged areas. Therefore, if your intended target is a significant proportion of the image size and the orientation/field centre of the 2 sets of images are not similar, it could result in a significant loss of otherwise useful data.

It certainly helps to get the images approximately aligned, but a slight rotation or shift isn't the end of the world. This is the result from 2 sessions, and I had some 14° rotation between them. Did not cause big problems. Rosette-8461_0s.thumb.jpg.8f3b88d93c5a2b4d1e10976e37f86d3d.jpg

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1 hour ago, michael.h.f.wilkinson said:

It certainly helps to get the images approximately aligned, but a slight rotation or shift isn't the end of the world. This is the result from 2 sessions, and I had some 14° rotation between them. Did not cause big problems. 

Agreed, rotations and shifts should not pose a problem if the largest target dimension (in image pixels) is quite a bit less than the smallest image dimension.

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2 minutes ago, Mr Thingy said:

How do you stack images from multiple sessions? Do you stack all in together (assuming similar temps) or stack by session then stack these together?

I personally stack each session, and then stack the resulting stacks, and by using weight maps produced during the stacking of each session odd edges are minimised if you have slightly different orientations. Astro Pixel Processor also allows you to do multi-session stacking, in which case you have to indicate which flats, darks etc to use on which lights. The advantage of doing it my way is I do not necessarily have to keep all subs on my hard disk, just the resulting stacks and corresponding weight maps. Stacking the results from different sessions is very quick too.

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3 minutes ago, michael.h.f.wilkinson said:

I personally stack each session, and then stack the resulting stacks, and by using weight maps produced during the stacking of each session odd edges are minimised if you have slightly different orientations. Astro Pixel Processor also allows you to do multi-session stacking, in which case you have to indicate which flats, darks etc to use on which lights. The advantage of doing it my way is I do not necessarily have to keep all subs on my hard disk, just the resulting stacks and corresponding weight maps. Stacking the results from different sessions is very quick too.

TYVM

Not sure if Deep Sky Stacker has provision for multi-session stacking. I may need to try APP instead.

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1 minute ago, Mr Thingy said:

TYVM

Not sure if Deep Sky Stacker has provision for multi-session stacking. I may need to try APP instead.

I used DSS for a while, then trialled APP, and promptly bought it. Well worth it in my experience, I find it much more intiutive, and it gives me much better results

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Here is the result of the area around Alnitak, combining a whole lot of sessions, with, or without Optolong L-eXtreme

St-avg-27447.0s-NR-x_1.0_LZ3-NS-full-qua-add-sc_BWMV_nor-AAD-RE-noMBB_1stLNC_it3-St.thumb.jpg.53978e8eb4bff93ddbefd19206cc1a80.jpg

Some edges do show up, especially between overlapping stacks taken with different filters, so of course you crop the result

St-avg-27447.0s-NR-x_1.0_LZ3-NS-full-qua-add-sc_BWMV_nor-AAD-RE-noMBB_1stLNC_it3-St-crop.thumb.jpg.3730d23767bc82b6e7850663ec3f3ad9.jpg

Still needs more data (even with 7 h 37 min of data). Note I did not do any denoising on these data

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DSS did NOT like that.

I had to go through all the frames to see if I had a rogue one.   Last nights session and the day before are both roughly centered on the heart of the heart.  I don't quite understand the tilt that I'm seeing here

bilde.png.766b2f718461d0baae7d47a076c74ac8.png

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I tried stacking data from 2 sessions separately, then stacking the subsequent images but DSS didn't like that, so I stacked the lot together. 

That seemed to work OK but then the conditions were similar. Only about 55 min of data so far, and still have colour to add, but already looks crisper.

 

M42_Ha_10.02.2021_Basic processing~2.jpg

Edited by Mr Thingy
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I tried stacking in intersection mode, and that cropped it this far in.   Just a quick and dirty edit to see what I had to work with.

Well,  I guess I'll just store the data from my first location for later.   I have 3 more clear nights(hopefully) at the location I'm currently at, so it's not the end of the world! 
I'll see what I have in 2-3 days! 😁
Autosave001-DeNoiseAI-denoise111111111111111.thumb.png.f6448dc0b2e249fedb9dff4cbc942d7d.png
 

7 minutes ago, Mr Thingy said:

Only about 55 min of data so far

Two sessions and only 55 minutes of data? : o
But it looks good though! Especially for less than an hour of data!

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1 hour ago, Pryce said:

I tried stacking in intersection mode, and that cropped it this far in.   Just a quick and dirty edit to see what I had to work with.

Well,  I guess I'll just store the data from my first location for later.   I have 3 more clear nights(hopefully) at the location I'm currently at, so it's not the end of the world! 
I'll see what I have in 2-3 days! 😁
Autosave001-DeNoiseAI-denoise111111111111111.thumb.png.f6448dc0b2e249fedb9dff4cbc942d7d.png
 

Two sessions and only 55 minutes of data? : o
But it looks good though! Especially for less than an hour of data!

Your image looks great. Real nice.

I'm quite pleased with my camera (ZWO ASI 183MM) - it seems really sensitve and give crips shots. The above image was shot in Ha, which helps sharpen the image I think.

Though I noticed about 5% of my subs had a line across them (also in the darks and bias), which I need to investigate.

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