Geometrics slant and tilt correction with Spcaudace

Geometrics slant and tilt correction with Spcaudace

Postby Benjamin Mauclaire » Sat Jan 02, 2021 4:12 pm

Hello all,

Some users asked me how to do manually slant and tilt geometric corrections. Here are some tips.

Usualy one won't need to know theses angles but only that his spectra are well processed with the pipelines.
These latter are based on the following automated functions that are ran in Audela's console such as:
- Tilt: spc_tiltauto 2d_stellar_spectrum.fit
- Slant and smile over x axis: spc_smilex2imgs 2d_calibration_lamp_spectrum.fit generic_name_of_stellar_spectra_to_be_corrected (ex.: vega-)

But it is possible to do all with "hands" as described in the following documentation's pages:
http://spcaudace.free.fr/docs/index.php ... metry.html
http://spcaudace.free.fr/fonctions.php#geom

1. gives you the tilt angle:
spc_findtilt 2d_stellar_spectrum.fit
2. rotate the spectrum:
spc_tilt2 2d_spectrum.fit angle(°) xrot yrot -> rotate the spectrum
where xrot and yrot are image's center coordinates

and

1. Measure, correct and store smilex/slant parameters in file out fits header:
spc_smilex 2d_calibration_lamp_spectrum.fit
Smilex/slant parameters are stored in the following fits kewords:
SPC_SLX1= 757.103 / [pixel] ycenter smilex
SPC_SLX2= 5.928086E-05 / [real] coef deg2 smilex

2. Use the parameters stored in the corrected 2d_calibration_lamp_spectrum and apply it to other spectra:
spc_smilex2img 2d_calibration_lamp_spectrum.fit 2d_stellar_spectrum_to_be_corrected.fit

Benji
Spcaudace spectroscopy software: saving you hundred hours of frustration.
Benjamin Mauclaire
 
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Re: Geometrics slant and tilt correction with Spcaudace

Postby Stan Gorodenski » Thu Jan 07, 2021 8:45 pm

I read with interest how to do a tilt and slant correction. To enter the commands, like spc_slant spectre_2D.fit
one has to be in console mode in Audela. How does one get in console mode? Where is it? I suspect it is explained in one of the topics in Help, but they are all in French at this time.
Stan Gorodenski
 
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Re: Geometrics slant and tilt correction with Spcaudace

Postby Stan Gorodenski » Fri Jan 08, 2021 7:35 am

After my post yesterday I went into Help and with Bing translated the part that is concerned with the Console. From what I read and from working with Aud'ACE (visu1) the console should automatically appear when I launch Aud'ACE but it does not. At the top of the screen there is a button called View. When I click on this there is a choice called 'Delete Console Content'. This indicates to me that there should be a console screen that is automatically displayed. Could it be that my computer operating system is not allowing the console screen to automatically appear? My operating system is Windows 7 Professional 64-bit.
Stan Gorodenski
 
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Re: Geometrics slant and tilt correction with Spcaudace

Postby Benjamin Mauclaire » Fri Jan 08, 2021 6:21 pm

Hello Stan,

Yes, when you Audela software, two windows are displayed: main Audela's window "Visu1" and the Console.
Press ALT-TAB keys on your keyboard to see list of all windows opened.
If Console isn't there, you have to removed the config file named audela.ini.
Find it on your hard drive.

Benji
Spcaudace spectroscopy software: saving you hundred hours of frustration.
Benjamin Mauclaire
 
Posts: 257
Joined: Thu Sep 29, 2011 10:14 am

Re: Geometrics slant and tilt correction with Spcaudace

Postby Stan Gorodenski » Fri Jan 08, 2021 6:24 pm

I think I figured this out. I have been using SpAudace for years just to get a gaussian fit to neon lines. Every time I launch Audela this dialog box comes up. It appeared to be somehow connected with exiting Aud'ACE because when I would click on the X in the upper right corner it would want to exit Aud'ACE. Not knowing what its purpose is and not being able to remove it (without exiting Aud'ACE) in just minimized it.

It just occurred to me that this might be the Console. In View I clicked on 'Delete Console Contents' and, sure enough, it emptied the contents in this dialog box. What made it more confusing as to what it actually is, is the fact that in Help when I click on Contents and then click on Getting Started, this dialog box is called Console but it is called Terminal in the Aud'ACE that I have on my computer. I checked a word translation to make sure Terminal does not mean Console in English, but it says the word 'Terminal' in French is translated to 'Terminal' in English.

I will now try to get some of the commands to work that is shown in Benjamen's post.
Stan Gorodenski
 
Posts: 7
Joined: Sun Jan 03, 2021 6:40 pm

Re: Geometrics slant and tilt correction with Spcaudace

Postby Stan Gorodenski » Fri Jan 08, 2021 8:43 pm

Hi Benjamin,
I applied the command
spc_smilex2img neon1.fit light1-5892a.fit
and it appears to have worked very nicely. The lines from my LHIRES III are curved and slanted (as you know they are in the LHIRES III design) and the command did a very nice job of making all the lines nice and straight and vertical. The spectrum was also corrected and it appears to have been corrected identically like the neon lines. Two hot vertical lines in the image of the spectrum ended up being re-oriented in a direction I would expect if the same correction that was applied to the neon lines was applied to the spectrum.

However, I just want to verify one thing. To use the corrected neon lines to calibrate the spectrum, it is very important that the same correction that was applied to the neon lines is exactly applied to the spectrum. Can you swear on a stack of Bibles that it is? :lol:
Stan Gorodenski
 
Posts: 7
Joined: Sun Jan 03, 2021 6:40 pm

Re: Geometrics slant and tilt correction with Spcaudace

Postby Stan Gorodenski » Fri Jan 08, 2021 10:32 pm

Hi Benjamin,
When I process a spectrum using IRIS I first correct the light spectrum for tilt and then I correct for slant. To correct for tilt, I run the command
L_Ori.
to get the tilt angle. If the orientation is, say, 0.070 degrees I correct the light spectrum for tilt with the command
tilt x 0.070
where x is the pixel center, vertically, of the light spectrum.
Then I select a range on each side of the light spectrum (which will later be used to crop the light spectrum) and use that range for cropping the calibration image. The range is usually about 40 pixels high (vertically). I then do a tilt correction by applying the same orientation value, 0.070 degrees, to the cropped calibration image with the command
tilt 20 0.070
where the value 20 is the center of the cropped calibration image, assuming it is 40 pixels high.

In this way I know the light spectrum and calibration spectrum are both identically corrected for tilt. How can I do this with Aud'ACE? To apply a slant correction from the calibration image to the light spectrum image I enter the command
spc_smilex2img neon1.fit light1-5892a.fit
In other words, I add '2img' to the command for just one image. I thought this might work the other way around for a tilt correction by executing the command
spc_tiltauto2img light1-5892a.fit neon1.fit
It does not work. Is there a way to apply the same tilt correction to the calibration image?

I compared correcting a light spectrum for tilt using Aud'ACE to correcting for tilt using IRIS. I found out that after correcting for tilt using Aud'ACE, the deviation from a perfectly corrected spectrum is 0.007 degrees. The deviation for the same spectrum using IRIS is 0.001 degrees. I know this is an extremely small difference between the two, but it appears Aud'ACE does not correct for tilt quite as accurately as IRIS. Would you agree?
Stan
Stan Gorodenski
 
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Re: Geometrics slant and tilt correction with Spcaudace

Postby Benjamin Mauclaire » Sat Jan 09, 2021 7:37 pm

Stan,

Yes this is of course the case.
Your logic is safe ;-)

Stan Gorodenski wrote:Hi Benjamin,
I applied the command
spc_smilex2img neon1.fit light1-5892a.fit
and it appears to have worked very nicely. The lines from my LHIRES III are curved and slanted (as you know they are in the LHIRES III design) and the command did a very nice job of making all the lines nice and straight and vertical. The spectrum was also corrected and it appears to have been corrected identically like the neon lines. Two hot vertical lines in the image of the spectrum ended up being re-oriented in a direction I would expect if the same correction that was applied to the neon lines was applied to the spectrum.

However, I just want to verify one thing. To use the corrected neon lines to calibrate the spectrum, it is very important that the same correction that was applied to the neon lines is exactly applied to the spectrum. Can you swear on a stack of Bibles that it is? :lol:
Spcaudace spectroscopy software: saving you hundred hours of frustration.
Benjamin Mauclaire
 
Posts: 257
Joined: Thu Sep 29, 2011 10:14 am

Re: Geometrics slant and tilt correction with Spcaudace

Postby Benjamin Mauclaire » Sat Jan 09, 2021 8:00 pm

Hi Stan,

Stan Gorodenski wrote:Hi Benjamin,
In this way I know the light spectrum and calibration spectrum are both identically corrected for tilt. How can I do this with Aud'ACE?


See the provious post, I answered to that question.
With pipelines all theses tasks are done for you.
Tilt and slant parameters are stored in the fits file header as I all ready explained.

To apply a slant correction from the calibration image to the light spectrum image I enter the command
spc_smilex2img neon1.fit light1-5892a.fit
In other words, I add '2img' to the command for just one image. I thought this might work the other way around for a tilt correction by executing the command
spc_tiltauto2img light1-5892a.fit neon1.fit
It does not work. Is there a way to apply the same tilt correction to the calibration image?


If you like manual task, all Spcaudace functions used to build pipelines are described here:
http://spcaudace.free.fr/fonctions.php

I compared correcting a light spectrum for tilt using Aud'ACE to correcting for tilt using IRIS. I found out that after correcting for tilt using Aud'ACE, the deviation from a perfectly corrected spectrum is 0.007 degrees. The deviation for the same spectrum using IRIS is 0.001 degrees. I know this is an extremely small difference between the two, but it appears Aud'ACE does not correct for tilt quite as accurately as IRIS. Would you agree?
Stan


As I didn't measured the tilt angle of your spectrum, the measured is only based on your "hands" (what you did and you method) and can't leads to a generic and neutral report.
Moreover what you do with hands can't be compared to automated process because each method has its own source of uncertainties on measurement.

Functions described in the list above are designed for seasoned programmers because I didn't wrote any documentation good enough to make it usable (not enough time). They were created to built the pipelines.
To get the best of Spcaudace you should use the pipelines and in doubt compare final result.
In fact Spcaudace has been designed to achieve all these boring but tricky tasks for a scientific exploitation afterwards that requires time to be freed up.

To get started quickly, you should do a training with the archive available in each pipeline tutorial and follow the steps described in it.
Then you process your own spectra.
- Computing the instrumental response [IR] (pipeline 1):
http://spcaudace.free.fr/docs/index.php?doclink=pipeline1.html
- Process night spectra (pipeline 2a=stellar targets, pipeline 2b=nebular starge
ts):
http://spcaudace.free.fr/docs/index.php?doclink=pipeline2a.html

Benji
Spcaudace spectroscopy software: saving you hundred hours of frustration.
Benjamin Mauclaire
 
Posts: 257
Joined: Thu Sep 29, 2011 10:14 am


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