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Accuracy difference - CPWI vs Handset OR skyportal - Starsense

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#1 SanjeevJoshi

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Posted 24 September 2020 - 01:05 AM

Something strange.  Could be a user error or I stumbled onto some useful finding.

 

been doing a bunch of testing for go to’s with these conditions:

 

1.  Precise polar alignment to start, using polemaster

2.  Then star sense auto - via controller, skyportal or CPWI

3.  For handset I tried entering nearest city.  For skyportal - on one iPad - GPS, on another nearest city.  on computer, lat / long, computer time.  Using WiFi dongle to computer

4.   Skyportal asks me to calibrate SS, handset does not ask (?).  Perhaps handset is remembering but I had removed between sessions, so could be slight difference.  CPWI, calibrate SS with one star (option when starting align)

5.  Do SS auto from handset, skyportal or CPWI.  No more alignment stars, no sync.

 

results?   Systematically, CPWI alignments are putting objects dead center or very close (a few clicks on motor at speed 4 or 5) of a 9 mm or 20 mm eyepiece.  Handset seems to miss the 20 mm nearly - hit or miss within the FoV, narrowly missed Saturn in 20 mm FoV.  Skyportal does in between - finds it in 20 mm but not close.

 

how can this be?   In the case of the handset, it could be its missing a prompt for calibrating SS and errors are adding up.   No such explanation for skyportal on iPad.

 

i have 3 observations each on handset, skyportal and 5 on CPWI.

 

could be user error, but wonder if CPWI is just a stronger / more precise approach.   I am using latest stable firmware on all devices.

 

I also tried reset alignment on handset - did not get prompt to calibrate SS and it did not make a difference in accuracy,  perhaps I had to go somewhere else in the menu.   But definitely did that on skyportal iPad.

 

Anybody else compare the 3 different ways?


Edited by SanjeevJoshi, 24 September 2020 - 08:28 AM.


#2 Michael_Swanson

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Posted 24 September 2020 - 01:26 AM

It is certain that while all three started with a common code base, they have been managed separately by different developers.

 

Best regards,
Mike Swanson
https://www.NexStarSite.com



#3 SanjeevJoshi

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Posted 24 September 2020 - 08:38 AM

Another curious thing I forgot to mention:

 

Skyportal on iPad finished 4 plate SS auto alignment + calibration + auto alignment and then told me (yesterday) my polar alignment was off by 0.02 degrees, and to do ASPA.   1.2 minutes - is that a lot of error?

 

I ignored the message because I trusted the polemaster precise work.  Polemaster alignment has been dead on every single time in combination with the use of CPWI, so it’s unlikely my polar alignment was off by 1.2 minutes - it’s more likely in my newbie view that the skyportal processs via iPad is not as accurate.
 

Just sharing these observations to help inform a broader insight.  I see so many posts about Star sense accuracy and repeatability etc.   It may be the differences in various implementations vs core functionality - which appears to be rock solid based on testing.



#4 skaiser

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Posted 24 September 2020 - 10:31 AM

Hi

 interesting testing.

for the starsense, when you calibrate, the calibration carries across all setups.

hand control, cpwi, SkySafari, etc all use a common calibration.

so , when you calibrate, be sure to do at high eyepiece power, ( crosshairs if possible) to get it as accurate as possible.

for alignment using the starsense, the accuracy is highly dependent on the number of points and where they are in the sky.

I have had my  alignment readings change by degrees, just by selecting additional points across the sky.

my testing of hand control “user auto alignment “ versus cpwi “ user auto alignment “ gives similar results, as long as I am careful to try and pick the same points in the sky for each alignment sequence.

take care

steve



#5 SanjeevJoshi

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Posted 24 September 2020 - 11:03 AM

Hi

 interesting testing.

for the starsense, when you calibrate, the calibration carries across all setups.

hand control, cpwi, SkySafari, etc all use a common calibration.

so , when you calibrate, be sure to do at high eyepiece power, ( crosshairs if possible) to get it as accurate as possible.

for alignment using the starsense, the accuracy is highly dependent on the number of points and where they are in the sky.

I have had my  alignment readings change by degrees, just by selecting additional points across the sky.

my testing of hand control “user auto alignment “ versus cpwi “ user auto alignment “ gives similar results, as long as I am careful to try and pick the same points in the sky for each alignment sequence.

take care

steve

 

Hmm, thank you for the info.

 

1.  how does Starsense store the calibration independent of the device used?  Where is it stored?  On the SS camera, the mount or the user devices (handset, ipad, computer)?  I got the feeling the calibration is stored in the device being used based on how the software works but it might be stored in the SS camera for all I know.  this would be good to nail down if somebody has the inside scoop

 

2.  If this were working across devices, i should never get a calibration required message on any device correct?  I remember getting one when i went to iPad

 

3.  I am  100% confident at least the X coordinate has shifted in the multiple calibrations i have done across sessions (based on remounting the SS for each session).   If no calibration is triggered, that also can lead to errors?

 

4.  I do agree i have not forced the same points to be used between the 3 devices - i have put it on auto every time and let it do its thing.  So is it possible the CPWI is using a different bias for selection than handset or skyportal?   That cant still explain why one is just more lucky than the other technique

 

5.  The difference in accuracy is meaningful, and if additional points are needed for handset or skyportal to match CPWI, that is good to know.   5/5 is a pretty good record for CPWI with no additional points to get dead centers.  The warning on polar alignment I think says it all.   if CPWI is working perfectly with the Polemaster alignment but skyportal says polar alignment is 0.02 degrees off -- seems the iPad Skyportal has not solved it accurately enough.   Maybe it needs more points as you are saying.

 

Btw to ensure correct alignment, i am using a lighted reticule 20 mm (with double cross hairs) to get to absolute center.  It is pretty much on track for 9 mm also, a very small deviation if any.   This is also how it shows up in the go to results.  This seems to be enough for CPWI based work.  Not sure why skyportal or handset would require more accuracy in alignment.



#6 robbieg147

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Posted 24 September 2020 - 01:48 PM

I usually use Starsence with CPWI but also the HC (as backup), and I have not noticed much difference between them in terms of accuracy. I guess with plate solving and syncing the actual error could be measured, I only do the standard Starsense auto align never add additional plate solves. 

 

I am afraid I am very distrustful of software and although the Starsense calibration is stored in the camera (depending on firmware version?), I calibrated Starsense with both the HC and CPWI, I would not assume the calibration carry's across devices. So if i were to use Skyportal on my phone I would do another calibration just in case.

 

As regards the Polemaster I would trust this over anything else even Sharpcap.



#7 donstim

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Posted 24 September 2020 - 02:18 PM

According to Celestron, CPWI uses a different and more accurate model than the hand controller. It is the same model used by the StarSense Autoalign accessory.

https://www.celestro...ontrol-software



#8 SanjeevJoshi

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Posted 25 September 2020 - 12:55 PM

I think CPWI is just a more solid solution overall, especially since wifi dongle on AVX and built in wifi on Alt Az mount are working flawlessly for me.

 

I am planning to use a dedicated laptop (to control the overall system) to do polar alignment + CPWI for starsense calibration + starsense alignment + sync where needed + go to.    Based on how well wifi is working for me (inside and outside the house with lots of networks), I have no distance limit at all for my laptop, so i can keep it at a comfortable distance (whatever suits).   Use the HC for slewing and fine focus.  I like to be at the scope when i do these two things, and HC is perfect for both.

 

This in my view gets the best out of the system.   iPad / tablet stuff with skyportal is fine too but a laptop makes things so much better overall.


Edited by SanjeevJoshi, 25 September 2020 - 12:55 PM.


#9 skaiser

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Posted 25 September 2020 - 03:12 PM

I think you will find the starsense cal numbers will always change by a few digits, even if you don’t remove it from the scope and you run the same software. But this is not enough to change alignment accuracy by very much.

also, cpwi does a great job of system control,but I really enjoy linking in SkySafari pro to use its sky map while being able to still use CPWI.

My curiosity was kindled with this conversation on Polar alignment accuracy so I experimented last night .

i ran a polar alignment using a ASIAIR Pro and sharpcap.

as you may know, both use a similar alignment technique.

take picture near the pole, rotate RA on mount , take another picture, then calculate the offset.

they then tell you how far off on each axis and walk you through adjust, image snapshot, reading, adjust, until you get to a desired alignment accuracy.

anyway the alignment readings for both software pkgs were identical, within a few tenths.

i will say the sharpcap was a little easier to use since it took continuous snapshots and gave continuous readings.

 unfortunately , My normal viewing location has no view of the pole area. So I have to rely on starsense for alignment. To make it harder, this spot only has a western clear view. I could do drift alignment to tweak it but I don’t have the patience and starsense seems to give me enough accuracy, as long as I choose my point properly.



#10 SanjeevJoshi

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Posted 25 September 2020 - 04:18 PM

I think you will find the starsense cal numbers will always change by a few digits, even if you don’t remove it from the scope and you run the same software. But this is not enough to change alignment accuracy by very much.

also, cpwi does a great job of system control,but I really enjoy linking in SkySafari pro to use its sky map while being able to still use CPWI.

My curiosity was kindled with this conversation on Polar alignment accuracy so I experimented last night .

i ran a polar alignment using a ASIAIR Pro and sharpcap.

as you may know, both use a similar alignment technique.

take picture near the pole, rotate RA on mount , take another picture, then calculate the offset.

they then tell you how far off on each axis and walk you through adjust, image snapshot, reading, adjust, until you get to a desired alignment accuracy.

anyway the alignment readings for both software pkgs were identical, within a few tenths.

i will say the sharpcap was a little easier to use since it took continuous snapshots and gave continuous readings.

 unfortunately , My normal viewing location has no view of the pole area. So I have to rely on starsense for alignment. To make it harder, this spot only has a western clear view. I could do drift alignment to tweak it but I don’t have the patience and starsense seems to give me enough accuracy, as long as I choose my point properly.

thank you yes, it seems the polar alignment packages do a terrific job.   Polemaster software has some quirks with Windows, but I know sharpcap pro is 10 dollars a year.   Are you using the pro version which is paid?




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