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AI based wave front sensing and collimation

Collimation
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#401 Corsica

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Posted 10 November 2023 - 10:02 AM

I answered my own question. The video stack is slightly crisper than a single 10-sec frame, but the collimation scores and the suggested adjustments are very similar. Moreover, a video stack with a small ROI will only capture on-axis stars.

 

But Astrosurface can easily extract the red channel from an OSC fit file and convert it to monochrome, so it wasn't wasted effort.

SKW standard models for astronomy and field collimation are trained to account for seeing conditions, specifically using Kolmogorov's turbulence model for "long" exposures, which typically range from 10 seconds to one minute depending on the aperture of your telescope. You can find detailed model specifications on our e-store (below a link fo reflectors with apertures <13" model):

https://www.innovati...up-to-330mm-13/
 

This implies that there is no necessity to employ lucky imaging techniques, although it is possible to do so. As you may have observed, the results from lucky imaging and SKW long exposures are quite similar. While stacking frames has limited benefits for SKW wavefront measurement, it can prove valuable if your mount experiences any tracking issues during exposures of up to one minute, helping to mitigate mount drift.

 

I would recommend starting with "short" exposures at the initial stages of collimation, such as 10 seconds, to expedite the process. Additionally, you can optimize the process by cropping the image around the star, allowing SKW to process a smaller frame for finding on suitable stars. If you choose to crop, I recommend a subframe size of approximately three times the minimum size value provided by the SKW GUI (see expected frame size).

Once you achieve a score of around 8 or higher, you can transition to longer exposures to fine-tune collimation. Longer exposures help reduce the wavefront distortions induced by atmospheric seeing even more. While using the red channel or a red filter can somewhat mitigate seeing effects, this is not a strict requirement for SKW.



#402 fetoma

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Posted 10 November 2023 - 11:08 AM

Licensing question. I have several scopes - Vixen VC200L;Vixen R200SS;Meade 8" SCT and an Intes-Micro M73.

 

I'm interested in the SkyWave Collimator unlimited (UNL) mathematical model 450S for reflectors with apertures up to 330mm (13″) license. Would I need to buy one for each scope for almost $2K total?



#403 Corsica

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Posted 01 December 2023 - 05:09 PM

Licensing question. I have several scopes - Vixen VC200L;Vixen R200SS;Meade 8" SCT and an Intes-Micro M73.

 

I'm interested in the SkyWave Collimator unlimited (UNL) mathematical model 450S for reflectors with apertures up to 330mm (13″) license. Would I need to buy one for each scope for almost $2K total?

Each SKW model is specifically trained for a particular telescope. Therefore, you will need one UNL or PPU for each telescope.

However, for a given model, you have the flexibility to adjust certain parameters within a realistic range. You can freely modify the wavelength, pixel size, and local seeing conditions. Additionally, it is possible to utilize a focal reducer (FR) with a reduction factor down to 0.6x.



#404 DaveDE

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Posted 01 December 2023 - 06:50 PM

I have a Dall Kirkham iDK. Its specified focal length is 2128mm yet my plate solved images currently come out to 2123mm. Does Skywave base its spacing adjustment "+/-" indications on the specified 2128mm or does it compute what the best spacing should be to minimize spherical aberration solely from the wavefront analysis? In other words, can Skywave's recommended spacing be different than the manufacturers spec?

 

A very important consideration for me is that the collimation will result not only in optical congruence of both mirrors but also that the primary mirror M1 is optically congruent with the focuser tube. I wish for this to be the case so that no sensor tilt is introduced when the focuser is rotated. Can Skywave be used to first optically align the M1 reference to the telescope backplate/focuser/camera? iDKs do not have a fixed primary mirror and mine may be out of alignment with respect to the focuser tube. Any suggestions on how to do this part of the alignment?

 

I downloaded SkyWave and played with it a bit. I created an instrument and connected to it, and loaded a raw inage. It starts off with a Trial Mode and the center of the target blocked but then if I Simulate the blue center block goes away and a point is plotted on the target. If I simulate again, a different point appears. I'm confused as to what is going on here. If I'm in Trial mode why is the center (results above 6) becoming unblocked and why does re-simulating produce a different result?

 

I also requested a Trial model for my particular telescope about a week ago and have not received anything. How long does the Trial model for my scope take to receive?

 

thanks

 

Dave



#405 Corsica

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Posted 02 December 2023 - 09:54 AM

I have a Dall Kirkham iDK. Its specified focal length is 2128mm yet my plate solved images currently come out to 2123mm. Does Skywave base its spacing adjustment "+/-" indications on the specified 2128mm or does it compute what the best spacing should be to minimize spherical aberration solely from the wavefront analysis? In other words, can Skywave's recommended spacing be different than the manufacturers spec?

 

A very important consideration for me is that the collimation will result not only in optical congruence of both mirrors but also that the primary mirror M1 is optically congruent with the focuser tube. I wish for this to be the case so that no sensor tilt is introduced when the focuser is rotated. Can Skywave be used to first optically align the M1 reference to the telescope backplate/focuser/camera? iDKs do not have a fixed primary mirror and mine may be out of alignment with respect to the focuser tube. Any suggestions on how to do this part of the alignment?

 

I downloaded SkyWave and played with it a bit. I created an instrument and connected to it, and loaded a raw inage. It starts off with a Trial Mode and the center of the target blocked but then if I Simulate the blue center block goes away and a point is plotted on the target. If I simulate again, a different point appears. I'm confused as to what is going on here. If I'm in Trial mode why is the center (results above 6) becoming unblocked and why does re-simulating produce a different result?

 

I also requested a Trial model for my particular telescope about a week ago and have not received anything. How long does the Trial model for my scope take to receive?

 

thanks

 

Dave

All optical surfaces are subject to tolerances relative to the specifications, which is inevitable. Telescope makers pair M1 and M2 mirrors to optimize results for a specific telescope. Consequently, the actual focal length of any telescope rarely matches the specified one, meaning there are no two identical telescopes.

A few percent difference in the actual focal length is common and should be expected. For a nominal value of 2,128mm, this tolerance can result in a difference of a few inches. During telescope assembly, the spacing between both mirrors is adjusted to minimize spherical aberration using metrology tools. This spacing is influenced by the M1 and M2 pair, as mentioned earlier in relation to tolerance.

Additionally, the telescope's focal plane relative to M1 varies from one telescope to another. Manufacturers typically set the M1 mechanical position to maintain a constant back working distance from the telescope's visual back. This distance is where the camera sensor plane should be located.

 

SKW's engine is a wavefront sensor, providing aberration data and functioning as a metrology tool. SKW models are based on nominal (specified) focal lengths, apertures, and central obstruction values. However, users can freely adjust parameters like wavelength and pixel size. Tolerances (typically a few percent) on these values have minimal impact on wavefront results, generally causing differences of just a few nanometers. When using SKW, one should use the telescope's specified optical parameters.

 

A word of caution regarding measuring the focal length with plate solving: Given that the difference is usually small (in your case, only -0.25%), one may question whether the inherent measurement errors in plate solving are as significant as the actual focal length difference we are looking for. Also attempting to adjust the M1 to M2 spacing based on this information to match the specified focal length is not recommended since the actual focal length is unknown, and the spacing was likely adjusted accordingly at the factory. Changing it may worsen the situation. The only reliable way to adjust the spacing is by measuring the optical effect, spherical aberrations, using optical metrology tools like the Ronchi test or wavefront sensing (e.g., SKW).

 

The tilt of the optical train relative to the telescope's optical axis results in a defocus gradient across the field of view. Since SKW measures aberrations (not FWHM values, which combine everything), you can independently align both mirrors (congruence) despite such tilt because you are primarily addressing coma rather than defocus. In the Zernike decomposition, these two balanced aberrations are orthogonal (independent) of each other. However, this isn't true if you use FWHM or HFD values, as they combine everything and make it challenging to separate collimation and mechanical image tilt.

It's important to note that an uncollimated scope (from a mirror congruence standpoint) will have a tilted optical axis and, consequently, a tilted focal plane relative to the sensor plane, even if both become congruent after collimation. In short, seeing tilt (defocus gradient) in the image for an uncollimated scope is normal, and attempting to correct tilt before achieving scope collimation (congruence) is not recommended. This is why FWHM or HFD values are less suitable and challenging to use.

This is also why we have optical metrology tools when doing optics and optical alignment, using the right aberration at the right place and time.
 

In your case, after addressing on-axis coma, you can use SKW to examine defocus across the field to measure mechanical tilt, if present. SKW Pro offers a direct tool for this, while SKW collimator provides a defocused error (in microns) vertical gauge on the left side of the SKW collimator tool. By observing how this error changes for various stars across the field (with the focus position unchanged), you can calculate the tilt. The goal is to achieve a balanced defocus across the field. Any tilt makes defocus unbalanced relative to the on-axis point.

 

Since version 5.5 (currently at 5.6), SKW automatically offers a trial model for any SKW instrument settings. There is a built-in generic model, eliminating the need to request a trial model. However, this generic model is limited, and SKW provides collimation feedback only for scores below 6 (coma aberration). Beyond that, you'll need to purchase a model tailored to your telescope.

The SKW simulation function allows you to explore the software without providing actual FITS images. Each time you click the simulation button, SKW generates a new randomly defocused image with some aberrations. You can view this image in the small thumbnail image window next to the collimator tool target (bottom left). Collimator scores obtained using the simulator are based on the simulated random images, so they change each time. This function is designed for software evaluation and training.

 

For more detailed information on SKW and its functionalities, you can refer to the SKW documentation, which is also accessible within SKW as interactive help:

 

https://www.innovati...Collimator.html


Edited by Corsica, 02 December 2023 - 09:59 AM.

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#406 DaveDE

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Posted 02 December 2023 - 01:35 PM

This all makes sense and is great information. Thanks for taking the time to address my questions in detail.

 

I think I can collimate and minimize tilt for all sensor rotation angles using this tool.

 

 

Dave

 

 

p.s.

 

The documentation referred to appears to be a bit out of date because it recommends requesting a custom trial model for the user's telescope.

 

skywave.png



#407 Corsica

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Posted 02 December 2023 - 01:47 PM

This all makes sense and is great information. Thanks for taking the time to address my questions in detail.

 

I think I can collimate and minimize tilt for all sensor rotation angles using this tool.

 

 

Dave

 

 

p.s.

 

The documentation referred to appears to be a bit out of date because it recommends requesting a custom trial model for the user's telescope.

 

attachicon.gif skywave.png

You're most welcome.

Good catch, thanks, we need to update the documentation accordingly.



#408 RonaldNC

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Posted 13 December 2023 - 08:36 AM

Gaston,

 

I bought a new computer and would like to transfer my license/credits to the new machine.  I sent a message via your website a few days ago, but haven't heard back.  Is there a particular procedure that I need to do to accomplish the transfer?

 

Thanks,

Ron



#409 Corsica

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Posted 13 December 2023 - 08:50 AM

Gaston,

 

I bought a new computer and would like to transfer my license/credits to the new machine.  I sent a message via your website a few days ago, but haven't heard back.  Is there a particular procedure that I need to do to accomplish the transfer?

 

Thanks,

Ron

Hello Ron,

Maybe the email was lost in some SPAM filter. Could you send it again to my email gaston@innovationsforesight.com?
Sorry for the issue.



#410 RonaldNC

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Posted 14 December 2023 - 02:59 PM

Hello Ron,

Maybe the email was lost in some SPAM filter. Could you send it again to my email gaston@innovationsforesight.com?
Sorry for the issue.

Thanks Gaston!

 

I responded to you request for information.  Hopefully what I sent was what you need.

Thanks,

Ron



#411 Corsica

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Posted 15 December 2023 - 08:40 AM

Thanks Gaston!

 

I responded to you request for information.  Hopefully what I sent was what you need.

Thanks,

Ron

Dear Ron,

I got your email, sorry for any delay but the end of the year is quite a rush time...

I replied to your email, here is my answer:

It appears that the files you sent me are your current models, rather than new requests.

If you have installed a new version of SKW on a new machine from scratch, the first step is to create an SKW instrument for each telescope. To initiate a new request, follow these steps for each telescope:

 

1   Navigate to the SKW instrument settings for each telescope.
2   Scroll to the bottom of the page and locate the "NN model" field
3   Click the "Request" button next to it, which will open a pop-up window.
4   In the pop-up window, select permanent model, provide your order number, and save the request to a file.

5   Attach both of these small text files to an email and send them to me.
 


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#412 MichiP

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Posted 25 January 2024 - 01:46 PM

Hi,
 

does some have the excelfile stored for creating the pattern in N.I.N.A.?
It's no longer available on the Dropbox and was originally posted here: 

https://www.cloudyni...2#entry12196135

 

Would be great if some can share it with me. 

 

Thank you.

 

Regards,
Michael 



#413 BobT

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Posted 26 January 2024 - 09:05 AM

Here you go:

 

Attached File  Calculate coordinates for off centre astigmatism frames - Final.xlsx   13.1KB   15 downloads

 

If I'm not mistaken I believe it is (was) available on the IFI website.


Edited by BobT, 26 January 2024 - 09:06 AM.


#414 Corsica

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Posted 26 January 2024 - 10:09 AM

Hi,
 

does some have the excelfile stored for creating the pattern in N.I.N.A.?
It's no longer available on the Dropbox and was originally posted here: 

https://www.cloudyni...2#entry12196135

 

Would be great if some can share it with me. 

 

Thank you.

 

Regards,
Michael 

Here is a link to the Paul Evans's Excel calculator:
 

http://innovationsfo...es - Final.xlsx



#415 MichiP

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Posted 30 January 2024 - 09:19 AM

Thank you! :) 



#416 petersellis

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Posted 28 March 2024 - 06:27 PM

Hi Gaston,
I have been using SkyWave for a little while now,  it is lovely piece of software and very easy to use.
Recently I purchase a new C9.25 EdgeHD  SCT for a remote dark site, when I tested it  gave the following results: Coma 3.4, Astigmatism 9.9, Spherical 9.8 . Given that it came all the way from China to Australia, it didn’t surprise me, given the number of bumps and bangs it probably received along the way. My final Collimation using SkyWave was: Coma 10, Astigmatism 9.7, Spherical 10. This is probably a dumb question, but I will ask it anyway, my second last adjustment gave Coma 9.9, Astigmatism 9.9, Spherical 10.  Should I have left it at that second last adjustment, rather that pushing for 10 out of 10 for Coma?

                                                Peter



#417 Corsica

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Posted 03 April 2024 - 11:17 AM

Hi Gaston,
I have been using SkyWave for a little while now,  it is lovely piece of software and very easy to use.
Recently I purchase a new C9.25 EdgeHD  SCT for a remote dark site, when I tested it  gave the following results: Coma 3.4, Astigmatism 9.9, Spherical 9.8 . Given that it came all the way from China to Australia, it didn’t surprise me, given the number of bumps and bangs it probably received along the way. My final Collimation using SkyWave was: Coma 10, Astigmatism 9.7, Spherical 10. This is probably a dumb question, but I will ask it anyway, my second last adjustment gave Coma 9.9, Astigmatism 9.9, Spherical 10.  Should I have left it at that second last adjustment, rather that pushing for 10 out of 10 for Coma?

                                                Peter

Dear Peter,

 

Congratulation and thank you for the feedback. The difference between 9.9 and 10 scores is quite small, so I wouldn't worry too much about that. Also, you may still experience some fluctuations caused by seeing-induced wavefront errors (low-frequency content of the seeing power spectrum), depending on your exposure time. Please refer to the recommended model exposure time, which is a function of your scope's f# and the atmospheric seeing. Here is a link to one of our model, they all have the same specifications on this regard:

 

https://www.innovati...up-to-330mm-13/

 

To speed up the process, I suggest using exposure times in the range of 10 to 20 seconds and considering the longest ones only towards the end for fine-tuning/assessment.

 



#418 petersellis

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Posted 04 April 2024 - 01:07 AM

Dear Peter,

 

Congratulation and thank you for the feedback. The difference between 9.9 and 10 scores is quite small, so I wouldn't worry too much about that. Also, you may still experience some fluctuations caused by seeing-induced wavefront errors (low-frequency content of the seeing power spectrum), depending on your exposure time. Please refer to the recommended model exposure time, which is a function of your scope's f# and the atmospheric seeing. Here is a link to one of our model, they all have the same specifications on this regard:

 

https://www.innovati...up-to-330mm-13/

 

To speed up the process, I suggest using exposure times in the range of 10 to 20 seconds and considering the longest ones only towards the end for fine-tuning/assessment.

Hi Gaston,

Thanks for your reply, I thought I might have been splitting hairs on that one.  The results above where based on 60, 10 second exposures, the best 20% stacked.  As an academic exercise after I posted this enquiry, I went through the 60 frames one by one,  to see what the variation looked like, coma was consistently 9.9  to 10 , astigmatism did vary a little 9.6 to 10, in fact, I had 4 frames out of the 60 that gave 10 10 10, a perfect score. The night wasn't the greatest of nights for collimation, it was windy and the seeing conditions >=2.0 arcsec, the results are impressive. I'm also glad I purchased the UNL Model, it allowed me to tinker around like this without running out of credits. Now all I need is somes decent weather so that I can do some long exposure (5 hours plus) Astrophotography.

 

                                   Peter


Edited by petersellis, 04 April 2024 - 03:57 AM.


#419 Newfie Stargazer

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Posted 08 April 2024 - 08:52 AM

Gaston,

 

I have steered away from RC scopes due to the perceived difficulty with collimation that I have always heard of, however since discovering your software, I am considering giving it a go, as I am in the market for a longer FL scope.  I have watched the wonderful Youtube video by Peter Cox on the procedure to collimate an RC scope and I do have a question prior to considering a RC scope purchase.

 

As the 6, 8, and 10" RC scope versions have the focuser attached directly to the primary mirror, would I still be able to use your software to achieve a respectable collimation without performing any alignment corrections to the focuser using an aftermarket tilt plate?

 

Jim


Edited by Newfie Stargazer, 09 April 2024 - 04:31 AM.


#420 BobT

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Posted 09 April 2024 - 08:07 AM

Jim,

 

I believe the later model 10" GSO RC's (at least the truss tube model) have the focuser attached to the rigid backplate, I think the smaller diameter tubes still have it attached to the mirror but I haven't kept track of that market in a while.  You might check with one of the vendors to make sure.

 

BobT



#421 Corsica

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Posted 09 April 2024 - 06:33 PM

Gaston,

 

I have steered away from RC scopes due to the perceived difficulty with collimation that I have always heard of, however since discovering your software, I am considering giving it a go, as I am in the market for a longer FL scope.  I have watched the wonderful Youtube video by Peter Cox on the procedure to collimate an RC scope and I do have a question prior to considering a RC scope purchase.

 

As the 6, 8, and 10" RC scope versions have the focuser attached directly to the primary mirror, would I still be able to use your software to achieve a respectable collimation without performing any alignment corrections to the focuser using an aftermarket tilt plate?

 

Jim

Dear Jim,

 

The collimation of an RC telescope, involving the alignment of both mirrors, is typically achieved by addressing coma (on-axis) and astigmatism (off-axis). Mechanical tilts at the camera level, from the focuser or elsewhere in the optical train, can introduce defocus gradients across the field. As SKW provides data categorized by aberration type, you can separate these factors.

 

Since the focal plane may be tilted when the scope is not collimated (mirror optical axes not congruent), I recommend addressing any tilt after collimating the scope initially. The procedure usually involves correcting coma, typically on-axis. However, in an RCT, third-order coma is corrected across the entire field, which is a fundamental property of an RCT.

 

If you utilize both mirror tilt/tip controls for collimation, it's crucial to use the primary mirror (M1) to cancel the coma and the secondary mirror (M2) to balance the off-axis astigmatism. Failure to follow this process could lead to a diverging procedure, resulting in the absence of coma across the field and yet significant astigmatism in certain field positions.

 

After the collimation, you can inspect for any defocus gradient, indicating a tilt in the camera sensor plane relative to the focal plane, arising from any source (focuser, FW, camera, ...), but not anymore from the scope itself.


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#422 Newfie Stargazer

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Posted 10 April 2024 - 04:17 AM

Gaston,

 

So to summarize, collimate, using SKW and established procedures (i.e. as per Peter Cox's video) for an RC scope, the primary (to correct coma) and secondary (to correct astigmatism) mirrors first, and then deal with any potential defocus gradients caused by a mechanical tilt (focuser) after.

 

I appreciate the technical explanation.  However, your vast technical knowledge (PhD level I assume) on the subject can sometimes muddy the waters (in this case explanation) for us with only an amateur understanding of the theory, so please forgive me when asking for clarification.

 

Jim



#423 taraobservatory

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Posted 28 April 2024 - 04:27 AM

I've had a request to share the spreadsheet I created to calculate the coordinates for off-axis test stars. 

This is fairly rough and ready - you obviously have to input your own image size (in arcmins) and decide how far "off axis" you want your test star images to be. 

I hit the limits of my knowledge on "how to do spherical trigonometry in excel" in terms of working out the arcsec moves for various values of Declination, so since I always use Edasich as a target star, this spreadsheet has 60 degrees Dec as a hard coded value - clearly you can adjust to whatever value you wish to use. 

Someone cleverer than me could clearly improve this :-)

 

I plug in the RA and Dec values reported by iOptron commander when I have Edasich centred, and it then gives me a set of 8 RA and Dec values correctly spaced from field centre, which I can easily move to in turn using the manual move buttons in commander. Same would obviously work with other scope software. 

 

For me the main benefit of using precise coordinates for this (rather than the wholly manual method I first tried) is that since all the test images are a fixed distance from field centre, it means that any variations in astigmatism scores measured by SKW are true variations and not just caused because astigmatism will get worse further from field centre. 

 

https://www.dropbox....es CN.xlsx?dl=0

 

Hope it helps, questions welcome. 

 

Clear skies.

 

Paul

Hi Paul, 

 

 

Im just learning about skywave now and I was wondering if you had that spreadsheet? I would like to make a script in voyager using this method. 

 

Kind regards

Roger 



#424 BobT

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Posted 28 April 2024 - 10:46 AM

Roger,

 

It's on the IF! website;  http://innovationsfo...es - Final.xlsx


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#425 Rasfahan

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Posted 28 April 2024 - 05:27 PM

Hi Paul, 

 

 

Im just learning about skywave now and I was wondering if you had that spreadsheet? I would like to make a script in voyager using this method. 

 

Kind regards

Roger 

Hello Roger,

 

I‘ve tried myself on this but didn‘t get very far. If/when you get this to work, would you be willing to share the script?

 

Best regards,

Torben


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