Platesolving in APT

[Demonperformer]

APT offers two forms of platesolving: PS2 (which requires approximate coordinates) and ASPS (which does it "blind").

Now, for reasons which would be a bit of a red herring to go into here, my preferred choice is PS2, but this does rather depend on exactly what "approximate" means.

My "worst case" scenario:
As I set up my equipment each time, I reckon this will be my first GOTO. I polar-align the mount using polemaster and have my scope roughly in "home postion" (the counterweight bar is as close to "down" as gravity will take it, and the dovetail bar is pretty much over the counterweight bar as judged by eye - any suggestions for getting it easily, more accurately "homed" welcome).

Now, from this position I will do a GOTO and I always try to make my first GOTO to an obvious (=bright!) star and it is always within about 45 degrees of the pole (Capella/Deneb or closer). But, with all the by-gosh-&-by-golly approximations I have used up to this point, it can be a few degrees out. It is at this point that I use the eyepiece, slacken the clutches and go looking (hence choosing an obvious star!). Hopefully APT will obviate this necessity, and brings me back to my original query: when using PS2 in APT, how "approximate" can "approximate" be? I have never actually taken the trouble to measure the error (not sure how I would with my current procedure), but is "a few degrees" (or 10 degrees even - if a 45 degree slew introduces a bigger error than that, I have bigger problems than platesolving!) good enough?

I suppose that, if it all works well, my ultimate goal would be to avoid this extra step altogether and go straight to the object I want (a 100-degree slew to an object dec10S and identifying where I land with no problem would be the ideal), but only if I can achieve it with PS2. I can live with this extra step if it means I can use PS2 rather than ASPS.

I have gone through the "pointcraft and plate-solving" section of the manual, but cannot find an answer to this question, so what do those who use the system think: how "approximate" can "approximate" be?

Thanks

[LightBucket]

If you use the blind solve option, it does not have to be near, but will take a bit longer, assuming you have both platesolve programmes installed, this is perfect for your scenario..

[Demonperformer]

This is why I specifically said:

20 minutes ago, Demonperformer said:

for reasons which would be a bit of a red herring to go into here, my preferred choice is PS2

So having to install ASPS is not "perfect".

[LightBucket]

27 minutes ago, Demonperformer said:

This is why I specifically said:

So having to install ASPS is not "perfect".

Well it would make life much easier, but no problem, just trying to help..

[fireballxl5]

Maybe my experience and details of my procedure will help?

I have a very similar procedure based on PS2, imaging using MaxImDL which has PinPointLE built-in...

1. Position my scope CW down/pointing at Polaris (gravity/eyeball is the level of accuracy used) and cold start the mount (powered by Gemini 2).

2. Go-to bright star near intended target (at focal length 1100mm and a small CCD this is often outside the FoV).

3. Take an image of the star field and save file.

4. Check ordinates of bright star in SkyMap Pro and enter these into PS2 to solve (100% reliable ) - PinPoint LE in MaxImDL isn't as good for solving with only rough coordinates with my eye-balled initial alignment and blind solving almost always fails in my experience  - EDIT: forgot to add sync mount on solved coordinates!

5. Goto bright star (again) and focus scope.

6. Goto imaging target, frame and go!

6 a) If part way though a multi-night imaging project, load previous image and plate solve in MaxImDL using PinPointLE with coordinates from SkyMap Pro (could use PS2 equally well). Not sure why the RA/Dec aren't always saved in the FITS file but hey-ho!

6  Goto centre of solved image to frame and go! (sometimes I need to do this twice for pixel perfect re-alignment).

7. Wait for the clouds to roll-in lol

HTH, 

Andy

[Demonperformer]

Thanks Andy. That looks pretty much like what I want to achieve. Step 2 looks like PS2 can cope wherever you move in the sky on your first goto? If so, that will more than meet my requirements and I won't have to install ASPS.

Thanks.

[mikeyj1]

easiest way is link to Stellarium or CdC, start that running first, select the object from the menu in APT , and it fills in the coordinates for you and then you can solve ps2

 

[StuartJPP]

I use APT and at the beginning of a session I point the scope towards the home position (roughly) and sync the mount to that position. Then slewing to any target is near enough for both ASPS and PS2 to be able to successfully plate solve by clicking the "<<Scope Pos" button to populate the approx RA and approx DEC fields with where the mount thinks it is pointing towards.

Once synced I haven't had any problem with either of the two methods when clicking the "<<Scope Pos" button to give both a fair chance of knowing where your mount is basically pointing.

You do need to ensure that your pixel scale is correct (focal length and pixel size) otherwise neither will solve.

My pixel scale is not massive (Full frame camera @ 500mm) so maybe that makes mine more forgiving to initial pointing errors.

[Pompey Monkey]

Do a plate solve from your home position. Then do a goto++

Your home position should be pretty close to where the mount thinks it is.

[Demonperformer]

Thanks, Paul.

I think that is probably a really good suggestion. It is always that first "hopeful" goto based on no definitive data that causes me concern, but this will give me a confirmed starting point/direction. What a simple solution.

Thanks.

[spillage]

I have started to keep one copy a light image from my targets in a separate folder. I can just start everything up and load up one of these images, solve it, add solved results and then goto++.

 

I guess it depends if you have to strip down your gear every session.

[Demonperformer]

32 minutes ago, spillage said:

I guess it depends if you have to strip down your gear every session.

This is what I have to do. 

[spillage]

Then as @Pompey Monkey mentioned, set up and from home position take a single shoot, click "scope position" and solve. Sync the results then either choose target from list or load up a previous image. Have you also installed any custom targets?

[stash_old]

Be careful using objects in APT database ,depending on the version of APT(i use 3.50), there are errors in the store database - look on the forum.

My steps for what its worth is (fixed obsys mount):-

1.  Choose object via ,for example ,CDC or use APT database objects.Slew to object.

If APT object goto (LOL) step (7)

2. Take image via "shoot"

3. Click on Pointcraft and click "scope Pos" then click "Solve" - APT will use PS2 - if you have come here from a failed "Solve" and "blind" doesn't work ry GoTo bright object and Sync but see notes below.

4. If PS2 solves image taken in (2) then click Sync/Show ELSE go to (3) and click "Blind"

5. Check CDC is showing scope pointing to object - has been know,rarely, for APT/CDC to get out of sync (BUG) is error then click on object again and goto step(2)

6. go to step( 10)

7. APT will continue taking images and Platesolving using PS2 until object found or  it runs out of time (as set up in settings)

8. If solved OK go to step( ) else goto step(2) and do a "Blind" solve.

9. Sync solved image with CDC.

10. Start imaging 

This works 90% of the time.

Notes.

a. you can call PS2/ASPS manually and see what the image being Platesolved looks like and the number of stars selected - also able to check image is correct. Plus you can check the logs.

b. The sky quality  plays a great deal in Platesolving so you may have to change your Camera/CCD parameters to give PS2 a chance.

c. If I cant Platesolve at all(Blind or Solve methods) it usually means I have knocked the mount on set up. So go back to basics - Balance,Polar etc

d. For me Platesolve works 90% of the time(its not perfect) but I have found some positions cause me problems - but I guess thats not PS problem but me !

e. IMHO ASPS backs up PS2 as another useful tool.

f. You should have to "GoTo"  bright  object and Sync but I do sometimes when I am really frustrated with Platesolving

 

[Demonperformer]

24 minutes ago, spillage said:

Then as @Pompey Monkey mentioned, set up and from home position take a single shoot, click "scope position" and solve. Sync the results then either choose target from list or load up a previous image. Have you also installed any custom targets?

Yes, as per post 311023, that is what I intend to do. Up until now, I have not used APT goto feature at all (hence this thread), but have used AT, which I always found to be tempramental at best. This is why I am exploring the APT option, so that would be a no to custom targets.

15 minutes ago, stash_old said:

click "Blind"

 

17 minutes ago, stash_old said:

do a "Blind" solve.

My understanding is that this will not work, as (as stated in the original post) I do not intend installing ASPS.

[spillage]

Here is the link to some custom targets. I find that most are fine but sometimes come across the odd one that is incorrect and just edit these as I find them.

[Demonperformer]

Is this going to be more efficient than using using the goto in eqmod/cdc and then platesolving in apt?

[stash_old]

12 minutes ago, Demonperformer said:

My understanding is that this will not work, as (as stated in the original post) I do not intend installing ASPS.

I did read you orig post but was pointing out ASPS does work ( I even use it with an old SWAZ GoTo and Synscan App) and I use it to Platesolve  on occasions where PS2 fails (and it does). Plus I use ASPS to goto the same position where I took an saved image on a previous occasion (used to use the same approach with Astrotortilla - another tool for Platesolving which can be used stand alone or with APT).  

Hey no problem we all choose the way that fits our mind set - clear skies! 

[spillage]

I find it useful and cannot remember the last time I fired up cdc. The standard objects list is good enough to start with. 

[stash_old]

1 minute ago, spillage said:

I find it useful and cannot remember the last time I fired up cdc. The standard objects list is good enough to start with. 

You probably already know this but you can import "lists" from Web Sites(and other means) like "What's in the Sky tonight" - but you do have to be online or prepared the list earlier at home. I find it useful for suggested object I may have forgot about.

[Demonperformer]

Right, sounds as if it is an alternative to using cdc, but as I require that to run eqmod anyway, it doesn't sound as if it will be of great benefit?

[Demonperformer]

I always concentrate on one object per session (or at most two, if my primary is going to disappear before 'packing-up time') so I will stick with cdc, I think.

[spillage]

@stash_old my link above is for the Burnham northern tour and the 100 best astrophotography objects.

APT will run eqmod and there is no need for cdc. I just use APT and PHD2. I would say I may fire up cdc or stellerium just to see what targets I can add to my ToDo list in APT.

I think by using APT rather than cdc you will not have to star align your mount.  I am sure when I used cdc I had to spend a while slewing to several objects, getting them central in the image and then syncing . With APT this is not needed. I guess as the software we are discussing all free then you have nothing to lose by trying them.

I remember using APT for months without using the platesovle part as it looked to technical, but now I am kicking myself for not using it sooner.

[Demonperformer]

I will have to read-up on APT's handling of eqmod. Until now, I have largely used APT as a 'shell' to run AT and then gone back to sharpcap for the actual imaging (My testing showed that sharpcap got my cameras to the required temperature in about 3 minutes rather than the 520 taken by APT, and I think we can all agree how valuable time spent imaging rather than cooling can be!). I will have to see about the relative benefits of cdc or a list (aka another file to help clog-up my new drive ).

However, now I am setting up everything "fresh" on a new laptop (that never has and never will go anywhere near the internet) it is a good time for me to look into streamlining operations (hence using PS2 rather than AT).

What is going to become my main imaging workhorse has just arrived today, so I ought to start getting to grips with all this 'in earnest'. Fortunately, the scope has brought with it the obligatory 72 hours of (you know what) weather!

[stash_old]

17 minutes ago, spillage said:

I remember using APT for months without using the platesovle part as it looked to technical, but now I am kicking myself for not using it sooner.

Yes I agree I used to use BYEOS for the same reason but APT is great.