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Need help with validation of a smart phone web application for star-hopping - that works like cell phone based digital setting circles

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#1 artik

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Posted 17 March 2021 - 04:14 AM

It is quite hard for find dim DSO objects especially in areas with light pollution. Typical easy (and costly) solution for the problem is to use GoTo mounts or to do more complicated task, especially for beginner: start-hopping. Find a start near-by and move towards your target. It is quite hard especially in urban areas when not that many stars are clearly visible.

 

There are many SkyMap like applications that point you to general direction of an object but they suffer from very poor accuracy especially on azimuth (~1-2 degrees for Alt and up to 20-30 degrees for Az)

 

So I developed a small free open source web application that combines internal motion sensors (gyro) and maps to first align on an existing easy to spot star and than select an object you looking for. The application guides to the desired target by measuring the changes in alt-az - similarly to digital setting circles. The assumption is that also absolute values of the sensors aren't accurate the relative small changes in the values are accurate enough to bring you to a target.

 

Manual: https://github.com/a...aster/README.md

Web Application (for smartphone): https://artyom-beili.../skyhopper.html

 

I tested in on my quite low spec affordable smart phone Samsung A31 with Chrome and Firefox and it works quite well - brings you directly to the target. I hopped between different Orion's stars. Hopped from Sirius to M41, M50. from Procyon to M44... with good success. However sometimes my phone's gyro looses accuracy and I need to realign from the beginning.

 

screenshot.jpg  small-skyhopper.jpg

 

However before I continue to add more features and improve the application I need to understand how well it behaves with different hardware

 

1. Does cell phone sensors provide sufficient accuracy to movement? 

2. What is reasonable telescope's FOV that works (1.5 deg, 1.2 deg etc)

3. How frequently it fails to work (gyro/gravity sensors goes out of sync)?

 

It would give me in important feedback to decide to continue with the development and how. I need to know weather application works or not on your hardware (phone + telescope) and if it provides an accuracy that good enough (what is your FOV) - note if applications like SkyMap don't work for you this likely wouldn't work either...

 

Thank You Very Much.


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#2 james7ca

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Posted 17 March 2021 - 07:04 AM

That's an interesting concept and it may have real value.

 

However, if you're going to have a computer handy (and a smart phone is basically a computer) why not add a small camera and just plate solve to find the target? It would cost a bit more but the results could be very accurate. In fact, with the right adapter you could mount the phone to a finder scope or just use one of the telephoto lenses that fit to a phone.

 

That said, if your digital setting-circle-like phone app did have sufficient accuracy then I'm sure many people would find it useful.

 

You may be able to find information on the internet about the accuracy of the inclinometers and gyros that are in today's phones. I know that I looked into finding out how accurate the compass apps are and what I found on the internet was NOT encouraging (basically, the compass in your phone probably isn't very accurate or repeatable). I tested the one in my iPhone and found that it varies by about +/- ten degrees, certainly not good enough to determine your true azimuth.

 

Also, some planetarium apps support a pointing mode where the display is supposed to indicate what you are looking at. However, I found that SkySafari wasn't very good at pointing accuracy, again it could be many degrees in error.

 

[UDPATE]

I can see that the OP's idea would offer a more immediate level of feedback than doing a plate solve, since it would naturally give almost immediate feedback as you moved the scope. However, you could do something similar with plate solving and it's also possible to create fairly good star plots that could be overlaid on the phone/computer's display to show you in realtime what direction you would need to move. That is, with a fairly decent alt/az or equatorial mounting once you know where the scope is pointing (originally) it should be possible to do a wider plot of the stars that would show what direction you need to move the scope, then just match up the stars from the camera's display to that of the star plot. Of course, you could also do multiple plate solves to kind of guide you along the way. Only problem (obviously), is that you'd need a camera to take the images that would be plate solved.

[/UPDATE]


Edited by james7ca, 17 March 2021 - 08:27 AM.

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#3 artik

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Posted 17 March 2021 - 08:21 AM

why not add a small camera and just plate solve to find the target?

This is exactly what "celestron starsense explorer" does - you connect cellphone to the telescope to special mount that contains a mirror and points the camera forward... In fact that what I was trying to do in first place. It is impossible to buy this adapter of generic telescope and it goes as bundle with selling a telescope that is why I stated working on it.

 

Indeed It isn't a big issue (I'm algorithms engineer who work with images all the time). So I collected images with Web Capture API and tried to find stars. Unfortunately I discovered that images I got have no signal - the camera settings kill all dark signal with negative offset and I could find only few brightest stars (Sirius, Rigel) and that was too unreliable for me to work with. I needed to have much better control of the camera which can be done probably only via Android API. So at this point I needed to go to full android SDK learning curve and ignore iPhone users. So I decided to go with something simpler and easier that gives me value.

 

Also development of such an algorithm would take much more time (that is limited resource considering it is free open source software).

 

You may be able to find information on the internet about the accuracy of the inclinometers and gyros that are in today's phones.

Actually I did. I found articles that talked about absolute "level" sensors and they had +- 5 deg but they didn't talk about relative error. For compass error was in tens of degrees and this is what I actually see.

 

However I don't have to have compass. I need to have gyro. There are two APIs - one gives true direction (using compass) another direction from start (using gyro).

Once you align I use gyro to measure changes in azimuth axis. So it should remain stable for few moves. I tested that it works for my phone before I started the development.

 

I tested the application with my smartphone and it worked nicely. I could find some objects that I couldn't find before - I managed to hop even by tens degrees. But I need more experience from users to understand how reliable this method across verity of phones/browsers.

 

If it works nicely for significant portion of users I want to add more features. Since with it you can enjoy from both learning night sky and easy finding dim objects.

 

Also, some planetarium apps support a pointing mode where the display is supposed to indicate what you are looking at. However, I found that SkySafari wasn't very good at pointing accuracy, again it could be many degrees in error.

Yes they are not reliable especially in bearing. That is why I implemented alignment step. 

 

Additionally unlike planetarium apps in my app "viewing" point goes from the top of the phone and it is actually better in terms of accuracy.


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#4 artik

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Posted 17 March 2021 - 08:36 AM

Only problem (obviously), is that you'd need a camera to take the images that would be plate solved.

Actually it is THE problem. I need to make sure that the camera signal is good enough.

 

Once again this is what Star Sense Explorer does. If they sell their cell-phone finder independently of the telescope I'd happily pay for one.

 

For me the biggest learning curve in implementing it is setup of all Android SDK and learning writing UI for it and learn its API.

 

That is why I implemented it as web API. You are welcome to open the app - it is just a simple combination of basic HTML, Canvas, stars DB in js format and some math implemented in JavaScript.



#5 artik

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Posted 17 March 2021 - 03:23 PM

I released a new version with following improvements:

 

  1. DSO database is now taken from OpenNGC project
  2. Added different icons for different object types
  3. Added filtering of DSO by magnitude and type
  4. Documentation typo fixes and updates

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#6 artik

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Posted 19 March 2021 - 01:16 PM

Last few nights I did some testing - here are my observations:

  1. It works very well I was able to find lots of objects that I hadn't dreamed to find before
  2. Even after several hops without realignment, the app nailed a star in Orion after aligning on Sirius withing 0.3 degree error.
  3. It is good idea to calibrate compass first - open application, make several "8 like" waves with the phone till compass points more or less correctly.
  4. Gyro-lost happens once in a while but not that serious
  5. I realized it also helps identify visible objects that you don't sure about.
  6. It helps a lot to increase time Android goes to sleep - I put 10 min and app continue to work

 

I also updated version:

  • Added planets
  • Limited the maximal DSO magnitude to 16 to prevent clutter and reduce the size of the file to download

So please provide some feedback! 

 

I think it can be great tool for beginner.


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#7 james7ca

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Posted 19 March 2021 - 02:06 PM

I would be interested in trying the app but I only have iOS devices (and one old Android tablet that I'm sure can't even be updated to a recent release). I think Apple may have removed web access to the gyro and accelerometer because they considered it a security risk (earlier versions of iOS used to allow you to turn this feature on or off, now that setting doesn't even seem to be available). Apparently some websites were using this data to implement things like key loggers. 


Edited by james7ca, 19 March 2021 - 02:32 PM.


#8 artik

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Posted 19 March 2021 - 02:35 PM

I would be interested in trying the app but I only have iOS devices (and one old Android tablet that I'm sure can't even be updated to a recent release).

It is WEB app. It is platform independent. I tested it with Google Chrome and Firefox. With Safari you probably will have no compass so initial azimuth will be manual but AFAIK you can install Chrome on iOS as well.

 

Just enter the link: https://artyom-beili.../skyhopper.html with the smart phone and try.



#9 james7ca

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Posted 19 March 2021 - 02:40 PM

It is WEB app. It is platform independent. I tested it with Google Chrome and Firefox. With Safari you probably will have no compass so initial azimuth will be manual but AFAIK you can install Chrome on iOS as well.

 

Just enter the link: https://artyom-beili.../skyhopper.html with the smart phone and try.

I tried it on my iPhone and it didn't work. Then I did some more research and I found out that Apple removed the gyro settings preference and they now require the web app to request authorization from the user before they enable gyro and accelerometer access.

 

Thus, if you want to support iOS you'll need to add that code to your app. Basically, it allows a pop-up alert that can be toggled by the user (either allow access or deny).


Edited by james7ca, 19 March 2021 - 02:41 PM.

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#10 artik

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Posted 19 March 2021 - 02:42 PM

I tried it on my iPhone and it didn't work. Then I did some more research and I found out that Apple removed the gyro settings preference and they now require the web app to request authorization from the user before they enable gyro and accelerometer access.

 

Thus, if you want to support iOS you'll need to add that code to your app.

frown.gif I don't have iPhone to test. I'll check what to do.

 

Also have you tried in Google Chrome?



#11 james7ca

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Posted 19 March 2021 - 02:47 PM

frown.gif I don't have iPhone to test. I'll check what to do.

 

Also have you tried in Google Chrome?

Using Chrome probably wouldn't help since the access is blocked (for security) at the OS level.


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#12 artik

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Posted 19 March 2021 - 02:55 PM

Using Chrome probably wouldn't help since the access is blocked (for security) at the OS level.

From this: https://vrprotour.co...ri-in-ios-12-2/ it should work.

 

Also checking how to request permission.



#13 james7ca

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Posted 19 March 2021 - 02:58 PM

From this: https://vrprotour.co...ri-in-ios-12-2/ it should work.

 

Also checking how to request permission.

Nope, as I said earlier that preference is no longer available in the latest versions of iOS. However, there are some examples on the web on how to request permission from the user to allow such access. 



#14 artik

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Posted 19 March 2021 - 03:09 PM

Ok I added request.

 

Can you check if this works: https://artyom-beili...hopper_ios.html it is version to check if I requested premissions correctly



#15 james7ca

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Posted 19 March 2021 - 03:21 PM

I never get the request to enable access. However, there may be some other security setting that is blocking the access to the alert/pop-up. I can still perform the "Align" step but after I select a target there are no updates to the pointing.


Edited by james7ca, 19 March 2021 - 03:24 PM.


#16 artik

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Posted 19 March 2021 - 03:31 PM

Ohhhh mybad. Fixed it. Try again - refresh - forget to update to correct function

 

Don't forget it is not main link: https://artyom-beili...hopper_ios.html


Edited by artik, 19 March 2021 - 03:33 PM.


#17 james7ca

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Posted 19 March 2021 - 03:54 PM

Still nothing and I used your most recent link. I also force quit Safari and deleted all of my history and deleted the data that you had stored on the phone. I may give Chrome a try tomorrow.



#18 luxo II

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Posted 19 March 2021 - 06:52 PM

This might be ok in an urban area, but in my country at many dark sky sites there's often no mobile phone network so web apps fail... they're dark, 'cause they're 50+ miles from any urban areas...

 

By the way you're wrong about the time to plate-solve using a standalone app - if anything its faster than doing it via the internet.

 

The time has indeed come for a standalone plate solving app - recent phones have more than adequate specs to do it in sub1 second, and the current crop of cameras are sufficient.

 

Astrometry.net, there's an opportunity if you can pull your collective heads out of linux commands, and build mobile apps that do this, and it only need involve stars down to mag 3 or so.


Edited by luxo II, 19 March 2021 - 07:16 PM.

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#19 artik

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Posted 20 March 2021 - 01:13 AM

This might be ok in an urban area, but in my country at many dark sky sites there's often no mobile phone network so web apps fail..

 

it is a single html page with javascript with all the objects database embedded inside. it does not communicate with the server at all. Once loaded it should work offline as well.

 

By the way you're wrong about the time to plate-solve using a standalone app - if anything its faster than doing it via the internet.

I hadn't planned to do it via internet. Just implement in JavaScript so I will not need learn new SDK/develop for iOS/Android

 

In any case I don't do plate solving,,, please refer to the manual I posted.



#20 artik

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Posted 20 March 2021 - 02:54 PM

I found the issue with iOS - I needed user to request permissions explicitly via click I can't do it on page load.

 

So I added a button that user need to press on to request permissions and I added some logs to see of something is going to stuck and where/

 

So I have two new versions:

 

https://artyom-beili...per_ios_v2.html - to check if I get device orientation information

 

Another (if first works) https://artyom-beili...per_ios_v3.html

 

To check if I can use compass information that is different for iOS/Saferi

 

please post screenshots for iOS...

 



#21 omomomo

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Posted 21 March 2021 - 12:18 AM

Both links work on my iPhone. 
 

screenshot is from 2nd link. 

Attached Thumbnails

  • 9619CCE8-6BA0-4916-ABD0-C06CCD5A6CAD.png

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#22 artik

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Posted 21 March 2021 - 02:01 AM

Thanks a lot.

 

I updated the main application with the fixes for iOS.

 

I also moved night mode and full screen controls to settings menu since they used only once in the beginning

 

Apparently there much more iPhone users in astronomy circles than in general population :-)


Edited by artik, 21 March 2021 - 03:44 AM.


#23 artik

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Posted 22 March 2021 - 03:08 PM

Updates:

 

  1. I added your GPS location information into the menu so you can validate if it is correct
  2. I added small video demonstration: https://youtu.be/3VXCSMidhe0

I'm still waiting for the reports:

 

I need to know how accurate/inaccurate it is;

 

I would be grateful if you can do an accuracy test by hopping between some clearly visible stars so you can both validate the result and measure actual error and report:

 

  • What smart phone and browser are you using?
  • What is telescope FOV so I can understand limitations?
  • What were the alignment star and target altitudes (alt - right bottom corner)?
  • How big was the hop in alt and az?
  • And of course did you find the target and what was the error in alt/az? (If you don't hit the star you can visually point the scope on it and see what correction app requests - it would be an error)

 

This really will help me to understand the limitations. It can be very good tool for new users who can't afford GOTO - but I need to understand the limitations (minimal FOV needed, maximal hop by altitude/azimuth, minimal-maximal altitude)

 

Without field testing I can't say anything meaningful - since so far on my smart phone/with my telescope it works mostly OK.



#24 james7ca

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Posted 22 March 2021 - 03:36 PM

The page linked in message #20 now seems to work on my iPhone.

 

What I'm going to do is attach the phone to my scope/mount and then use the mount's goto to see how closely the app agrees with the mount. That way I can even test inside and during the day. If it seems to work there then I can move outside to a simple alt/az mount.


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#25 artik

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Posted 22 March 2021 - 03:45 PM

The page linked in message #20 now seems to work on my iPhone.

Please use main version it already includes all fixes and improvements: https://artyom-beili.../skyhopper.html

 

 

What I'm going to do is attach the phone to my scope/mount and then use the mount's goto to see how closely the app agrees with the mount. That way I can even test inside and during the day. If it seems to work there then I can move outside to a simple alt/az mount.

What a great idea!!!

 

Thanks a lot!

 

If you work indoors  make sure it get the correct geographical position (under settings menu)


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