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PinPoint vs Astrometry.net

roe
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Too often I have had images that VPHOT couldn't process because it couldn't get a correct plate solution from PinPoint.  Sometimes, it appears, PinPoint fails totally, other times it gives clearly erroneous results (after all, most of us have charts).  Last night was another example.  I had V, Ic and B images of SN 2012aw and PinPoint failed on one of the images (Ic) and gave incorrect values for the other two.  I tried the images at home via MaximDL and got the same result.  I worked hard for those images and was darned if I wouldn't be able to report their values (the SN was clearly visible next to the galaxy, so I knew it was there).

I deleted the images from VPHOT and uploaded them to Astrometry.net which solved them in a bout 2 seconds and produced a new FITS image (with header amended to comment out the PinPoint WCS values and put in the correct ones).  These I downloaded from Astrometry.net and uploaded to VPHOT which processed them with no problem.

PinPoint vs Astrometry.net
padovan
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It happened to me,I have for the first time,in the last 2-3 days.A star that was the day before perfectly plate solved,same telescope,exposure eveything,todsay NOT solved,the other day different star same issue.

I tried with astrometry.net and just 1 min and that's it.Anyway since years I am using Photometrica-vPhot it is the first time.Maybe has to do with the last troubles with the server maybe not.

Any clue Geir?

Clear skies to all

Stefano 'T5' Padovan

In another post I pointed to
roe
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In another post I pointed to advancing technology as a challenge to VPHOT.  Plate solving technology is a case in point.  It appears to me Astronomety.net is far superior to Pinpoint and, perhaps, needs a test and consideration.  The previous two posts relate two anecdotes of Pinpoint failure, maybe there are more (I see it far too often but don't want to weigh down the forum with all the examples - it happened last night for example).  It is especially frustrating when Murphy's Law strikes on an "important" image as in last night when it failed on SN 2012cd for which I seem to be the only observer reporting data to the AID.  Maybe a user complaint to Bob Denny could get Pinpoint to handle cases where there is a bright star in the image (Mizar supersaturates the corner of the SN 2012cd image).

On the other hand the Astronometry.net software is free, open source and can be set up on a local computer.  (I used their free online service for a single image now and then.)

PinPoint problems - can we see your images?
KTC
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Jim, can you make your FITS images available...the version that would not solve in PoinPoint?  I'd like to examine them.

Thanks in advance.

PinPoint problems (2) - can we see your images?
KTC
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Stefano,

Can you make your 'problem' images available?  I would like to examine them.

Thanks in advance.

Pin Point problems
padovan
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Hi,

unfortunately I deleted the images just a couple of days later and...between tons of images on my ardrive it is hard to find them,anyway I'll give it a try.

Take care

Stefano PSD Padovan

images one plate solves other doesnt
sgor
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I can supply two images of V513 Cas taken back to back one plate solves the other doesn't. If you wish I can share them. 

 

..george

Images that won't plate solve
KTC
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sgor wrote:

I can supply two images of V513 Cas taken back to back one plate solves the other doesn't. If you wish I can share them. 

My VPHOT account is KTC if you want to share.  Or, you could attach them to a forum post here.  Either way works for me.

shared
sgor
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Shared with KTC thru VPHOT

 

..g

Ways to improve image quality (plate solving)
KTC
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sgor wrote:

Shared with KTC thru VPHOT

Thank you for the two images.  Some recommendations that will improve the odds of plate solving.  Some will be easier to implement than others

- VPHOT says airmass was about 2.4.  If that's true, you may want to consider staying at airmass 2.0 or lower...unless this is a really important target

- CCD FOV is only 12 x 8 arc minutes.  You are at the ragged edge of getting plate solves because your sky coverage is only about 100 square arc minutes.  Consider a focal reducer.  I use focal reducers on all SCT's here except scope K35 because the CCD is an STL-1001... (big) 20 micron pixels covering 1K x 1K ... FOV on that monster chip is 21 x 21 arc minutes...plenty of sky coverage for plate solving.

- Star profile size is 9 - 10 pixels FWHM.  That's very large.  (High airmass does not help).  If you do not get a focal reducer, consider binning that ST-10 at 3x3 instead of 2x2. 

- Your star FWHM is about 6 to 7 arc seconds.  That is big, very big.  (High airmass does not help.)  Think of ways to improve focus, guiding/tracking, and maybe OTA ventilation to reduce tube currents.  All SCT's here have carbon tubes, I have cut vent/fan holes and run fans all the time, and I use temperature compensation on the focusers.  If my FWHM is greater than about 4 arc seconds on K35 I am frowning.

- When I blink the two images against each other I can see a large number of hot/poorly calibrated pixels that are in a static pattern.  (And a smller number of random/additional pixels)  Can you improve calibration to reduce the number of these static hot pixels?

We can keep talking about this if you want, and we can do it offline, and maybe by phone if you want to get into this deeper.  Telescope Doctor is happy to do more analysis and troubleshooting to improve your rig.  The good news is that most problems can be fixed, or at least minimized.

VPHOT fails to find WCS solutions when it should
HOA
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There absolutely is a problem with VPHOT WCS. It does not always find a solution. For example, I took a series of 12 images of ER Ori during a 4-hour span. All 12 came back "red" for WCS solving. However, after uploading to Astrometry.net, all 12 easily found a solution. Then I re-uploaded to VPHOT, and this time all images were "green" for WCS solving.

This happens 10-15% of the time. I have not done any systematic experimentation, but it seems to happen when images are taken near or just below the celestial equator.

In all cases, image quality is very good to excellent with ample field size, S/N ratio, and availability of stars. The problem is that VPHOT inexplicably fails to find WCS solution when it should. Again, it seems to be related to where in the sky the images are obtained.

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