Author Topic: skyeye and other apps using magnetic sensors  (Read 6042 times)

Marko

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skyeye and other apps using magnetic sensors
« on: April 30, 2014, 06:20:20 PM »
Lets pick up the conversation from here.
I have been unable to paste all of emails due to some sort of character errors so just pick it up here ...

Marko

Let me roam the deep skies and I'll be content.

John Pierce

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Re: skyeye and other apps using magnetic sensors
« Reply #1 on: April 30, 2014, 09:03:51 PM »
On 4/30/2014 7:39 AM, Michael Packer wrote:
> Has anyone tried SkEye - an app for Android that uses your phone as a "push to" viewfinder for a Dob. (free on Google Play at https://play.google.com/store/apps/details?id=com.lavadip.skeye).
>
> It works like Google Sky, with the added twist that you can strap your phone to the optical tube of your scope, do an alignment procedure, then use the display on your phone as a virtual viewfinder for your Dob.  It's accuracy evidently depends on the accuracy of the accelerometer(s) and magnetometer(s) in your phone -- some phones are better, others are worse, according to some of the reviews
>
>

John Pierce

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Re: skyeye and other apps using magnetic sensors
« Reply #2 on: April 30, 2014, 09:06:20 PM »
On 4/30/2014 1:37 PM, Stephen Migol wrote:
> I have a copy of the application on my phone.  Unfortunately, we have the Hetch Hetchy pipeline running through our backyard and the magnetic field from these steel pipes renders the application useless there.  It should work nicely out in the field.  My phone's sensors tend to be jittery so it's not terribly great.  I have a cheaper phone so that may be a big factor.
>

John Pierce

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Re: skyeye and other apps using magnetic sensors
« Reply #3 on: April 30, 2014, 09:07:23 PM »
On 4/30/2014 2:25 PM, Alex wrote:
> The phone's gyroscopes/accelerometers/magnetometers are not stable and not precise enough for the task. I'm developing for the phones and know that for sure, as I have tried to make such a thing myself just recently with the top brand Android phone (Note III).

John Pierce

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Re: skyeye and other apps using magnetic sensors
« Reply #4 on: April 30, 2014, 09:08:20 PM »
On 4/30/2014 3:57 PM, Mark Johnston wrote:
> Don't bother reading this unless you are going to try or maybe buy SkyEye.   
>
> I too have been trying to use compass for android in software app and agree it is a well known serious downfall that  the compass and/or magnetic sensors are in general so bad that you never really know or can count on them to better than 10-30 degrees but can get 'lucky' given certain phones and if you have recently calibrated in the field just before use and at the same place as your scope.
>
> Yes I know there is an offset from true north as far as magnetic lines of force go but THAT is not the issue here.  People have had all sorts of issues with their sensors getting too much of an offset and having to try to 'degauss' them before they would work at all as I found was just ONE of my issues. 
>
> I have been working on an app based on Carter Scholz neat little device that is called 'Where is North' which shows where north is in the eyepiece for any given position.    I see numerous posts and agreement that the android accelerometers or not so bad but the magnetic sensors can be very erratic or can be ok and you never know what to believe.  Calibration is not the solution in general. Not repeatable and some phones are reported to be horrible always on those readings.
>
> forgive me for this off topic post but it does relate to the plug to use this nice little app mentioned.    I have wasted over 12 hours in working with and looking into this issue and is is quite 'sad'.  I hope that anyone who tries it simply goes in knowing that it is likely ok for handheld eyeball gazing but if it actually works for a narrow < 1 degree field of view I can assure you you will be VERY VERY lucky and should buy a lotto ticket that day as that is your lucky day.
>
> In short, if you have to verify it every time with a compass and re-calibrate X times then what exactly is the point???
>
> Marko

John Pierce

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Re: skyeye and other apps using magnetic sensors
« Reply #5 on: April 30, 2014, 09:09:54 PM »
On 4/30/2014 4:05 PM, Lynne Jolitz wrote:

 You can't use the sensor information filtered through a traditional java app. Instead you must access the raw data using the C++ dev library access to the underlying raw sensor information at the HAL layer (hardware abstraction layer). This actually got discussed at a Lab 126 talk a few months back.

 If you don't use *and* process the raw information appropriately, the slew lags, making the app too imprecise for your needs.  This is due to the lag induced by the filters and an inappropriate selection of mathematical distribution for use with astronomical equipment. One must use the raw data and then use the correct distribution (in this case, a Kent distribution). Then one uses techniques to minimize delays. It's actually a subtle area of app development  and not the province of script kiddies.

 Hope this helps. I'd like to see a better astro app for this purpose myself. Get developing. ;-)

mpacker

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Re: skyeye and other apps using magnetic sensors
« Reply #6 on: May 03, 2014, 07:01:04 PM »
Thanks for great feedback!
Michael
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Jrgose

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Re: skyeye and other apps using magnetic sensors
« Reply #7 on: December 27, 2014, 09:31:05 PM »
John, thanks.  Bad-elf claims their small GPS hardware plugins work with many astro aps:) Not sure if their location antenna would enhance what we need?  http://bad-elf.com/pages/compatible-apps

My "smart whatever" device still needs mechanical servos for telescope pitch, roll and yaw equivalents:)