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VSP inconsistency

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Eric Dose
Eric Dose's picture
VSP inconsistency

Last November, I used Variable Star Plotter (VSP) to generate charts for DW Ori, giving 8 comp stars.

Now I generate charts for very nearby DY Ori (actually closer to the comps), and I get no comps in the chart at all. And when I generate a new chart for DW Ori, I (usually) get no comp stars either.

If I start from scratch, from the AAVSO home page, the comp stars appear again. But when I go to Plot Another Chart to get my needed field of view and mag limit, the comp stars disappear. When I start over again, hit Plot Another Chart, and then go to Photometry Table for this Chart, I get only V and B-V, when the VSP form very clearly requested B, R, and I as well.

Then when I try to make a DY Ori chart (~ same field of view), no comp stars appear, even though VSX lists 8 and VPhot gives 8 in the field as well. So the comp stars do exist, but VSP omits every one.

If I regererate charts from an old chart ID, I get comp stars, but only in V and B-V, which is not what the original charts with that chart ID had (I have printed copies, thank goodness). This is not a matter of clicking the wrong thing or setting the wrong box--when I did these things in all of 2016, these problems did not exist. I have several hundred printed charts that worked just fine.

Can anyone enlighten me: What is going on here? When I now try to use VSP, I never know whether I'm going to get comp stars or not, even in the same field of view, I don't know what filters I'm going to get, and I can never--never--reproduce charts from a chart ID, which breaks the whole traceability that chart IDs were supposed to lend.

Any guidance appreciated.

tcalderw's picture


Can you give me a couple of example chart IDs to look at?  I'd like one from early in 2016 (before the Web site change-over) and one after.

I suspect that part of the problem is that hidden "state" is hanging around (or changing underneath you) in VSP between requests.



SGEO's picture
VSP anomalies


Your problem description appears to be two different issues: 1) the process of plotting a chart from the specification page, not getting the same result when you thought the input was the same. And 2) not being able to reproduce a chart from its chart ID.

To figure this out we're going to need exact, reproducible, examples. So, for any one with a VSP anomaly, please package up:
   - short description of the problem, what you think is wrong
   - the chart image: right click the chart and "save image as" <chartID>.png
   - the URL of the chart page: copy and paste it into the email. This is important.
   - if the chart is not matching an old, printed chart, scan that old chart and send it.
   - if you think the VSP specification page is not being interpreted properly, I'll need to see a picture of it. It will take 2 PrtSc captures pasted into Paint and saved as png's. Or use a full, scrolling page capture tool like SnagIt or Nimbus.
    - Zip up this evidence and email to

I'll do what I can. I share your concern: we have to be able to trust VSP.


WGR's picture


For item 2 above:  "And 2) not being able to reproduce a chart from its chart ID."

I remember that this problem was looked into in the past.  The original idea was to be able to input the chart ID, and get the same chart.  There is some reason while this does not work.  I don't think it ever worked.  As I remember, the same is not true of the Sequence ID. 

Arne will remember for sure.



BSJ's picture
Not being able to reproduce charts

Hi Gary,

I am pretty sure that the problem with not being able to reproduce old charts using the chartID is confined only to those charts created before about June 2015. That's when Will re-wrote VSP and corrected an earlier problem that prevented the comp star magnitude information from being preserved. As far as I am aware, using the chartID should produce reproducible results as long as the original was created after June 2015.

This is important to dig into. George's list of things to send when you see a problem is needed for troubleshooting properly.


SGEO's picture
Some of VSP's subtleties

- VSP has some 6.3 million chart requests on record. And it can reproduce any of those charts with the following caveats:

  - The chart will be presented as a chart, not photometry; you will need to transcribe the chart specs into the form to regenerate the photometry.

  - The more important difference that might exist is that the comp stars displayed and their mags will be based on the current data in VSD. This matches the notice shown on the bottom of the chart: "Warning: when using ChartID to plot a chart, the chart headers are pulled from VSX; they may have been updated since the chart was originally plotted."

This last issue, of showing the latest VSD information, was effectively disabled until recently because VSP was working from a cache. Given a chartID it would first look to see if it had saved the image of that chart and serve that instead of regenerating the chart. This was more of an oversight than a feature: the cache had grown to 200,000 images, some 30Gb on the web server and was causing performance issues; that cache had to be cleared.

If you have a chart display anamoly, please package up the evidence as described above and I'll check it out.



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