AAVSO/VPhot doesn't think image is plate solved

I am using Siril to process images for submission to the AAVSO’s VPhot photometry software. I use Siril to do the plate solving and save the new header.

However, after uploading the image to VPhot, it doesn’t think the image is plate solved. I assume there is some FITS value it is looking for that is not present. Any idea what that could be?

In addition, I notice that Siril doesn’t add the CALSTAT information. My image has been corrected with Bias, Darks and Flats. The header doesn’t indicate that.

I uploaded a different file to VPhot and with this one it did its own plate solve. Apparently the info from Siril was not enough. There are two possibilities:

  1. Siril generated all the info, but I didn’t save it correctly. I’m assuming that clicking the Save button will write the new header info. Is that right?

  2. Siril doesn’t write the full WCS info to the header. I notice that when VPhot plate solves it has added things like:

PA 2.69331715600E+002 [deg, 0-360 CCW] Position angle of plate
CROTA1 -8.93317156000E+001 [deg] Roll angle wrt X-axis
CROTA2 -8.93317156000E+001 [deg] Roll angle wrt Y-axis
CD1_1 -3.44137866361E-006 Change in RA—TAN along X-Axis
CD1_2 2.95008280641E-004 Change in RA—TAN along Y-Axis
CD2_1 2.95035364491E-004 Change in DEC–TAN along X-Axis
CD2_2 3.44106274968E-006 Change in DEC–TAN along Y-Axis
TR1_0 2.32749967619E+003 [private] X-axis distortion coefficients
TR1_1 4.65599986214E+003
TR1_2 -1.13938288130E+000
TR1_3 1.21275357490E+000
TR1_4 5.65640493357E-001
TR1_5 -3.23183285242E-002
TR1_6 -2.61889862535E+000
TR1_7 -1.64830297516E+000

That is apparently what it needs. Does Siril generate this and I’m just not getting it saved?

The TR keywords are just coefficient for distorsion and we do not use distorsion.
We are using wcslib to set keywords and we do respect the standard. (Long discussion with Mark Calabretta, creator of the WCS data).
When we test the Siril FITS WCS header with the appropriate WCS tool, it does respect the standard. So yes we are writing the full WCS informations as stated in the WCS publication, just what is needed.
Cd Matrix is enough to compute a good astrometry solution, crota are deprecated and should not be used anymore.

So I can’t tell you what it does not work. But yes, you need to save the file to get the FITS WCS data .

I will have to take it up with AAVSO to see why their software thinks the FITS isn’t plate solved when it is using Siril. Not a huge issue if they do their own plate solve.

Could you please comment on:

“In addition, I notice that Siril doesn’t add the CALSTAT information. My image has been corrected with Bias, Darks and Flats. The header doesn’t indicate that.”

The AAVSO software doesn’t like that the image hasn’t been marked as calibrated. It will flag it as such and researchers will (most likely) not use the data because it is suspect. I could add the CALSTAT data myself, but that is yet another step (and another app). It seems like Siril should be inserting this.

The problem with these kind of keywords is that there are not standard.
Each software can decide to add one so it is very difficult to handle every situation.

Well, Siril is billed for use in “scientific” imaging. I think AAVSO is one of the most scientific uses imaginable for amateurs. It is expecting the CALSTAT keyword so I think it is worth considering adding it. If this hasn’t come up before I’m a bit surprised.

Does Siril have a mechanism for adding an entry to the FITS header. That would at least prevent me from needing to fire up a different app to do so. I know ASTAP can do this but I’d rather not use it if possible.

Yes of course. but how many software use it?
Probably only one. We need to investigate why this keywords is needed because right now, I don’t see.

Not yet but it is on our plan.

I also want to clarify that I’m not really complaining about your software – I think it’s amazing. I’m just making suggestions for how to make it better. Thanks for all your hard work.

And I’m not complaining about your request :slight_smile:
But the FITS Header keywords forest is very dense. Each software using their own trees. With Siril we are trying to follow standard.

Yes, I understand that the FITS header keywords are somewhat of a mess. However I have found that at least MaxIm DL and ASTAP support it.


Improved reporting via keyword CALSTAT. Modified some messages.

I will also ask AAVSO if it might be possible to edit this info on their site so they know it is compliant.


I believe I have solved this in the short term at least. I have been using a Python script via pySiril to do my processing. I’ve found that I can use astropy to add the CALSTAT keyword right after saving the stacked lights. This seems to work.

Please could you open a ticket in our gitlab?
Will take a look next week.