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Simple Plate Solving question

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#1 Stelios

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Posted 21 April 2017 - 01:05 PM

I'm about to spend the evening getting plate-solving going (I've tried before unsuccessfully) with SGP Pro.

 

My question is simple: Assuming plate solvers (and blind fail over) are set up correctly: Can I plate solve by simply supplying the RA/DEC coordinates of the object I want to center on? Or do I *need* to supply an image to get the whole thing going? 

 

Of course telescope/camera will be connected via ASCOM and appropriate driver.


Edited by Stelios, 21 April 2017 - 01:06 PM.


#2 ismosi

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Posted 21 April 2017 - 01:17 PM

Astrometric solutions ('plate solving') require an image, otherwise, what would you be comparing?

 

In my automated imaging setup, I enter the RA/Dec of the target I want to image. Telescope slews to those coordinates. Image is taken, then the astrometric solution RA/Dec is compared to where my telescope 'thinks' it's pointing.

 

If it's not, synch/recal on the actual coordinates and re-slew. Repeat until within set error.

 

Does this help?


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#3 Alex McConahay

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Posted 21 April 2017 - 01:27 PM

Stelios

 

You may not have asked the right question.

 

Plate Solving is, by definition, something done to a picture.

 

However, I see you are using Sequence Generator Pro. If you are trying SGP for the plate solve, you do not need a picture before starting your session. You can tell SGP to slew the scope to wherever you want (by telling it the RA and Dec.) That does not require an image. SGP will do what is necessary to move the scope to the target area, and take a picture. It then PLATE SOLVES that picture to determine where it is. If it is where it belongs, fine. If it is not, it figures where it is, and moves again to where it should be, takes another picture, and Plate Solves again, and again, until it is in the right place, or runs out of tries (which you have specified.)

 

Before trying the slewing and Plate Solving, though, you should be reasonably well polar aligned, and your mount should be able to do a goto all by itself. If it cannot do that, then SGP will not be able to do it for you. (In addition, have your scale set before trying this if at all possible. )

 

Alex


Edited by Alex McConahay, 21 April 2017 - 03:08 PM.

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#4 S.Boerner

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Posted 21 April 2017 - 01:44 PM

I do find that SGP's plate solving is VERY dependent on the arcsec/pixel of your setup (press ctrl-E then camera tab and look for scale.)  If you are at all unsure about it or if your attempted solves don't work, consider going to astrometry.net and have them do one for you

(http://nova.astrometry.net/upload)  and use that value.



#5 anismo

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Posted 21 April 2017 - 01:48 PM

Also, Platesolve2 is much better than Elbrus . So it is worth setting it up. As mentioned earlier, The camera image scale information is very important for successful solves (I just take an image 1x1 and save it and upload the STF stretched version to astrobin (or astrometry.net) to get the arcsec/pix number). 


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#6 Ladyhawke

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Posted 21 April 2017 - 01:52 PM

If you are using SGP you can slew to an area of the sky that you want to image, center your target and Plate Solve. After doing this you can save the profile and when you need to go back, it will go exactly to the same location where you were before when you plate solved.


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#7 Stelios

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Posted 21 April 2017 - 02:05 PM

Stelios

 

You may not have asked the right question.

 

Plate Solving is, but definition, something done to a picture.

 

However, I see you are using Sequence Generator Pro. If you are trying SGP for the plate solve, you do not need a picture before starting your session. You can tell SGP to slew the scope to wherever you want (by telling it the RA and Dec.) That does not require an image. SGP will do what is necessary to move the scope to the target area, and take a picture. It then PLATE SOLVES that picture to determine where it is. If it is where it belongs, fine. If it is not, it figures where it is, and moves again to where it should be, takes another picture, and Plate Solves again, and again, until it is in the right place, or runs out of tries (which you have specified.)

 

Before trying the slewing and Plate Solving, though, you should be reasonably well polar aligned, and your mount should be able to do a goto all by itself. If it cannot do that, then SGP will not be able to do it for you. (In addition, have your scale set before trying this if at all possible. )

 

Alex

You are correct, that's exactly the question I was *trying* to ask smile.gif, and how I'd like to operate: Set my target coordinates, slew and center there. 

 

I have all the other "pieces," so maybe this will finally work! (I think my other failures may have been due to my scale set in one place but not in another).



#8 Stelios

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Posted 21 April 2017 - 02:07 PM

Also, Platesolve2 is much better than Elbrus . So it is worth setting it up. As mentioned earlier, The camera image scale information is very important for successful solves (I just take an image 1x1 and save it and upload the STF stretched version to astrobin (or astrometry.net) to get the arcsec/pix number). 

I do have Platesolve2 and local astrometry.net as backup. I believe I have the correct camera image scale (1.48") for my Rebel T3i and ED80, but your idea for checking it is excellent, thanks!



#9 Becomart

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Posted 21 April 2017 - 03:02 PM

1.48 sounds about the right ball park. I have a canon 100d which is 1.85. You'll never look back after plate solving, it makes setup so much quicker. No more messing around with alignment stars. 



#10 Stelios

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Posted 22 April 2017 - 01:34 AM

And guess what, it all worked! Plate-solved M51 in about 2 seconds! Seeing the galaxy dead center after the "center" command--priceless!

 

Thanks to everyone, including Jared and the rest of the SGP group for making the code work, and to Alex for his excellent tutorial. bow.gif bow.gif


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#11 Becomart

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Posted 22 April 2017 - 02:12 AM

Witchcraft I tell you...it's witchcraft!


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#12 dan_hm

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Posted 25 May 2017 - 09:34 PM

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!


Edited by dan_hm, 25 May 2017 - 09:35 PM.


#13 bobzeq25

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Posted 26 May 2017 - 12:28 AM

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!

How about trying it manually first?

 

I get in the vicinity.  Take a picture.  Plate solve it in PlateSolve2.  Look at where I'm pointed and where the mount thinks I'm pointed.  Do a little mental arithmetic to figure out the difference, slew that amount.

 

Voila, there it is.  <smile>

 

SGP nicely automates the process, but I don't see how it would hurt to figure out how to do i manually, first.



#14 dan_hm

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Posted 26 May 2017 - 05:20 PM

 

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!

How about trying it manually first?

 

I get in the vicinity.  Take a picture.  Plate solve it in PlateSolve2.  Look at where I'm pointed and where the mount thinks I'm pointed.  Do a little mental arithmetic to figure out the difference, slew that amount.

 

Voila, there it is.  <smile>

 

SGP nicely automates the process, but I don't see how it would hurt to figure out how to do i manually, first.

 

In my case though it wasn't really even putting it anywhere close to the target, so even if I did manually slew around it could very well take forever.  Tonight is supposed to be clear so I will try again and see if I can figure it out.



#15 dan_hm

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Posted 27 May 2017 - 10:06 AM

Well, Bob, after several failed attempts at automating the process I just did your method and it worked out.  I just can't get what is making SGP's slew & center feature fail.  At one point it looked like it was so close to being on target, but I foolishly forgot to increase the max number of attempts so it stopped after 3.  Then I increased the limit and tried again, but this time it pointed my scope in the complete opposite direction I wanted to go in.  



#16 Stelios

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Posted 29 May 2017 - 06:48 PM

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!

(2) and (3) in this list appears wrong. It almost seems as if you are doing some manual operation.

 

Correct order:

 

(1) Polar align.

(2) Sky align (two stars should be enough).

(3) In SGP, input coordinates, then "Slew Now" (note, it doesn't matter how far your scope is once you've done a sky align).

(4) In SGP, after the slew: "Center Now"


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#17 dan_hm

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Posted 29 May 2017 - 08:36 PM

 

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!

(2) and (3) in this list appears wrong. It almost seems as if you are doing some manual operation.

 

Correct order:

 

(1) Polar align.

(2) Sky align (two stars should be enough).

(3) In SGP, input coordinates, then "Slew Now" (note, it doesn't matter how far your scope is once you've done a sky align).

(4) In SGP, after the slew: "Center Now"

 

Thanks, I'll try it next night I get.  I was hoping to be able to avoid my CGEM's alignment routine altogether but I'll make do if needed.



#18 gambera

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Posted 29 May 2017 - 08:50 PM

Since this thread is about plate solve and image scale was mentioned, I've got a question about SGP and image scale and hopefully someone's got an answer.

I image with FF/FR and now you guys got me thinking if I have to input my image scale in SGP with FF/FR numbers?

AT80ED and ASI1600 here, 1.63"/pixel w/out FF/FR and 2.04"/pixel with FF/FR.

 

 

Stelios, I hope you don't mind hijacking your thread.

 

Thanks in advance 



#19 dan_hm

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Posted 29 May 2017 - 10:37 PM

Since this thread is about plate solve and image scale was mentioned, I've got a question about SGP and image scale and hopefully someone's got an answer.

I image with FF/FR and now you guys got me thinking if I have to input my image scale in SGP with FF/FR numbers?

AT80ED and ASI1600 here, 1.63"/pixel w/out FF/FR and 2.04"/pixel with FF/FR.

 

 

Stelios, I hope you don't mind hijacking your thread.

 

Thanks in advance 

Haven't used a focal reducer myself but since it's changing your focal length I believe you should input the values with the FF/FR included.


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#20 Stelios

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Posted 29 May 2017 - 11:46 PM

Since this thread is about plate solve and image scale was mentioned, I've got a question about SGP and image scale and hopefully someone's got an answer.

I image with FF/FR and now you guys got me thinking if I have to input my image scale in SGP with FF/FR numbers?

AT80ED and ASI1600 here, 1.63"/pixel w/out FF/FR and 2.04"/pixel with FF/FR.

 

 

Stelios, I hope you don't mind hijacking your thread.

 

Thanks in advance 

It's a related question. Like Dan, although I have no direct experience I can't see how you could avoid taking the reducer into account, as for practical purposes your scope behaves just like a scope with a shorter F/L. 



#21 Becomart

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Posted 30 May 2017 - 01:55 AM

Yes, you take the reducer into account otherwise platesolving might fail. 



#22 Daniel Dance

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Posted 30 May 2017 - 06:08 AM

 

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!

(2) and (3) in this list appears wrong. It almost seems as if you are doing some manual operation.

 

Correct order:

 

(1) Polar align.

(2) Sky align (two stars should be enough).

(3) In SGP, input coordinates, then "Slew Now" (note, it doesn't matter how far your scope is once you've done a sky align).

(4) In SGP, after the slew: "Center Now"

 

Why would you do it this way - enter Ra / Dec manually?

 

Get the SGP Framing and Mosaic Wizard.

 

1.  Frame your target exactly how you want it and save as an SGP target. (Do this the day before)

2.  Polar align

3.  Do a one star align (no need to be accurate at all.  I simply align a star using the long axis of my scope.  THAT'S IT!)

4.  Load your SGP sequence file (target)

5.  Right click on target - Select SLEW TO TARGET (rough slew)

6.  Right click on target - Select CENTER TARGET

 

That's it!  Perfect alignment!

 

Dan


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#23 S.Boerner

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Posted 30 May 2017 - 11:11 AM

Yes, you take the reducer into account otherwise platesolving might fail. 

My best suggestion is to take images with whatever optics and camera(s) you use, upload them to astrometry.net (http://nova.astrometry.net/upload) and have it solve them for you.  One of the items they return is the correct arcsec/pixel.  Use that value in SGP.



#24 Stelios

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Posted 30 May 2017 - 11:20 AM

 

 

I'm still not entirely sure how to replace Goto with plate solving on my CGEM with SGP.  This is what it seems I'm supposed to do, after making sure I'm on the right profile with the image scale of my camera:

 

1. Polar align

2. Copy coordinates of intended target from Cartes du Ciel

3. Point scope in rough direction of where my intended target is

4. Open up sequencer window in SGP, click on gear icon next to "Target," paste coordinates, slew and then center

 

But when I tried this it didn't put my target in the FOV.  I'm using a widefield setup too (ASI1600 + WoStar 71).  Am I missing something here?  I'm a big dummy and need a handholding!!

(2) and (3) in this list appears wrong. It almost seems as if you are doing some manual operation.

 

Correct order:

 

(1) Polar align.

(2) Sky align (two stars should be enough).

(3) In SGP, input coordinates, then "Slew Now" (note, it doesn't matter how far your scope is once you've done a sky align).

(4) In SGP, after the slew: "Center Now"

 

Why would you do it this way - enter Ra / Dec manually?

 

Get the SGP Framing and Mosaic Wizard.

 

1.  Frame your target exactly how you want it and save as an SGP target. (Do this the day before)

2.  Polar align

3.  Do a one star align (no need to be accurate at all.  I simply align a star using the long axis of my scope.  THAT'S IT!)

4.  Load your SGP sequence file (target)

5.  Right click on target - Select SLEW TO TARGET (rough slew)

6.  Right click on target - Select CENTER TARGET

 

That's it!  Perfect alignment!

 

Dan

 

Don't quite see how this is easier (your step 1 and 4 take longer than cutting and pasting two coordinates)) but it's certainly another way. You could do a 1-star align with the "enter coordinates" method as well. 


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#25 jpbutler

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Posted 30 May 2017 - 02:49 PM

I almost always goto astrobin.com search for the dso I am going to image, sort on likes, and then copy the url to the target dialog in sgp. It will then use those coordinates including camera angle for the slew. 

 

It's not like I am imaging anything that hasn't been done before. 

 

I tried images from dso  browser dot com too and it also worked great. 

 

After you slew to the image and platesolve it, you can also right click on that image and center on a different portion of it. 

 

Sgp offers many ways to get there. 

 

John


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