VPhot Plate Solution - Important Revision

American Association of Variable Star Observers (AAVSO)
Sat, 07/25/2015 - 16:34

Fellow VPhot Users:

A revision has been made to the plate solving operation of VPhot that the VPhot team hopes will improve the operation of this important tool. For a small number of users, it will impact your use of VPhot significantly but only if you do not carry out a simple step which most other users have already carried out. That is, if you do not conduct this operation, your images will be classified as "failed". 

As has been mentioned recently in other posts, about 15% of images uploaded to VPhot fail to plate solve mainly because they do not provide an image scale associated with their VPhot Telescope Setup (under admin). Lack of this one value causes these images to undergo a lengthy but unsuccessful plate solution process (3 catalogs x 60 seconds each) with a default image scale (2 arcseconds per pixel) which fails 90% of the time but not without a significant expenditure of time. The arithmetic doesn't lie. If you upload 100 images without an image scale present in your Telescope Setup, I'm sure you can see that up to 180s (3 minutes) of precious processing time are wasted for each image or a total of up to 300 minutes (5 hours)! We have tried workarounds for this problem but concluded that the effort need to re-write the code to simplify the experience of a few users who do not spend any time reading about the operation of VPhot but just hope that a black box will produce a valid solution without any understanding of the process, was not worth it! frown

So, if your images are not being processed by VPhot, go to your Telescope Setup and confirm that the information boxes are properly and completely filled in. Either Create New Telescope Setup or edit your existing Setup (see below).

We have not made this change lightly but in the best interest of the majority of VPhot users. I suspect a few users will be impacted by this change but actually note that your images were being failed anyway so it really makes no difference to you?

BTW, for users who take images with different binnings (e.g., 1x1 and 2x2) on the same scope, note that you need to set up two separate scopes (different names) with the correct plate scales provided in each case. For users who pre-platesolve their images, no change is necessary.

Our hope is that this is a trivial request. If you need assistance, post a message to this thread but please read help files first and try before you ask? Thanks.


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American Association of Variable Star Observers (AAVSO)
Plate Scale

Hello Ken

Thanks to the Vphot Team for this improvement.  We should probably mention, that if your image scale is off by 25%, your images will not plate solve.  So when you are checking your profile to make sure an image scale is present, make sure the value is current.



American Association of Variable Star Observers (AAVSO)
Specifying your platescale

To clarify a bit:     In your VPhot Telescope Profile you specify a Header Name for your telescope along with the platescale. This Header Name needs to match the TELESCOP parameter in your image's FITS header so that VPhot can find the correct platescale.

For those using the iTelescope system the TELESCOP parameter should be GRASxxx, eg GRAS024 for  iTelescope 24. The VPhot team will work to maintain the appropriate profiles for iTelescope as well as the SSON system.

Its a bit frustrating when you see VPhot failing to solve your image (ie WCS set to red in your image list). I'm working on a way for you to receive an explanation for a WCS failure. Meanwhile, if examining your telescope profile doesn't clear the problem, send me a note with the filename and date of submission and I'll dig out the explanation code from the activity log. (send a note with filename and date to SGEO@GASilvis.net

Ken mentioned the statistics prompting the change in protocol: iIn a recent sampling of 11,033 images (13 days worth) 644 failed plate solve, 368 of these because no platescale was provided. The change we are making would automatically fail these images because of the lack of platescale, saving a lot of queue time. On the other hand in this sample 41 images were successfully plate solved with the default platescale. The change means VPhot will no longer try to solve these images. Bottomline: you are responsible for providing VPhot with an appropriate platescale via the telescope profile mechanism.