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VPHOT USING WRONG FITS HEADER

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GaryH
VPHOT USING WRONG FITS HEADER

I took some DSLR images of Melotte 111 and processed them with AIP4WIN into seperate calibrated green and blue fits images.and then used AstroImage J to edit the fits headers. I uploaded the green image to VPHOT first to make sure it had the correct air mass, was plate solved and indicated as being calibrated. I next edited the blue image fits header. Since these two images are from the same raw file they were exposed at the same time, etc, thus I made everything like the green image fits header except changing the OBJECT to "blue" for identification and FILTER to "B". Note that I did not copy the green image fits header into the blue fits header. In AstroImage J I edited each line as needed. The Available Images Page indicates the green image has the correct air mass, is plate solved and calibrated but the blue image shows 0.0 air mass, not plate solved but is calibrated. I then looked at the blue image fits header in VPHOT and noticed it is actually the fits header of the green image. I have successfuly used this same technique for other images. Please help.

Gary

MZK
MZK's picture
Same Technique??

Hi Gary:

In what sense did you "used this same technique for other images"?

Are you saying that you did EXACTLY the same thing for another DSLR image and it gave different results?

I'm not sure why you made the OBJECT header 'blue"? You noted that it had Filter "B". That should make them different.

VPhot does not like to see images with the SAME date/time. It does NOT like that and will fail/cause problems. So this may be several things going on?

Please share the images with me at MZK and SGEO. Also, please provide an answer to my question above about technique. VPhot was not designed for DSLR images and we know there are some issues that we hope to fix some day? It causes extra effort to be taken and may not always work as expected!

Ken

GaryH
VPHOT USING WRONG FITS HEADER

Hi Ken,

For other images I edited the calibrated green FITS header by loading the fits image into AstroImageJ and then editing the header by inputing the needed info (OBJECT, DATE-OBS, FILTER, CALSTAT, AIRMASS, RA & DEC). Next the fits image was uploaded to VPHOT. If VPHOT showed the image having the correct airmass, plate solved and calibrated then I knew the fits header must have been ok since it worked. Then I used the same procedure for the blue image. As for different results, it worked so it is different.

I entered "blue" into the OBJECT title "MELOTTE 111 BLUE CAL AIP78" to reconize in the Available Images page to help me identify blue image from the green image. I do not believe it causes any difference to VPHOT.

I was wrong about the airmass being indicated. Was a problem in an earlier attempt to upload. I do not know what made it appear this time.

Based on your comment about using the same date/time I just uploaded a blue image with the time advanced by one minute. No success, same problem.

Please tell me how to share the images and I'll send them.

Gary

SGEO
SGEO's picture
VPHOT USING WRONG FITS HEADER

Gary,

- You can share images from the Images page by clicking the checkbox and then click the Share link above the image list. That takes you to the share page where you put in "MZK, SGEO"

- Note that DSLR images should have filter names TG, TB and TR as they are not precisly V, B and R. You tell VPhot how to handle them from the telescope profile page: There is section called Mappings where you can mapt TG to V, TB to B and TR to R.  The only way to properly report these images as V, B or R is if they have gone through the transform process.

Share the images and we'll see if the system is confusing fits headers.

Thanks,
George

 

GaryH
George,

George,

In Filter Mappings:

1. Under Value in FITS header (FILTER keyword) I enter TB for the blue image. 

2. Under Standard Filter I enter B

3. Do the same for green and red.

4. In the image fits header enter for Filter: TB, TG or TR as applicable

Is this correct?

I'm trying to use VPHOT to get the instrument measurements and then derive the color and magnitude  transformation coefficients using Excel to plot. I tried the Transformation Generator but could not getting the Anaconda to work so figured it would be faster to do the plots. Eventually I'll get Anaconda to work.

Once I have the transformation coefficients do I change the Filter mappings back to default by clicking the "X" to remove the mappings?

Did you get the two images I shared?

Thanks,

Gary 

SGEO
SGEO's picture
Timestamps for DSLR debayered images

If you debayer a DSLR image into 3 (TB, TG and TR bands), these three images should have the same timestamp.

In the past VPhot was confused by this, but that was a bug fixed a while ago.

So don't dither the timestamps!

George

GaryH
IMAGES SHARED

Hi George,

 

Thanks for the sharing instructions. Simple! Before sending them I looked at the blue image fits header and it has some how changed to the original. Meaning it has the OBJECT and FILTER for the blue image, not as before for the green image. But still not plate solved. I have no idea what happened. I did notice the time is as I originally used for the green image (since they are both from the same raw image). Ken mentioned images should not have the same time so yeaterday I advanced it by one minute yet no success. I do not know if one minute suffices, should it have?

I looked at the filter names in the scope profile. Do I need to have the transformation coefficients to map? I am trying to image standard fields to get the transformation coefficients. Guess I'll  need to study the VPHOT manual further.

Thanks,

Gary

SGEO
SGEO's picture
Shared Melotte images

- The problem you have now it that the blue image did not plate solve; you can't extract photometry unless the image is solved. If the OBJECT name was the same, then you could share WCS solutions. Especially useful for DSLR layes since you know they are the same spot in the sky. So, note 1: don't change the object names just to get a color tag. The images display already notes the filter band in VPhot.
Further, you should not add camera information to the object name. At some point you will want this field to match up to VSX, and if its more than just the object, it will fail that step.

So, reload the images with proper object name, "MELOTTE 111". If blue fails WCS, you will be able to use the Update WCS function to fix that up.

George

 

 

GaryH
Shared Melotte images

Hey George,

Sorry for the late reply. I changed the blue and green fits headers per your recommendations and both images plate solved with out needing to do an Update WCS. THANKS!

Can the name of the file used for each image listed in the Image List page be displayed on that page? I know that info is available in the Uploaded Images/View Processed Images page but it would be easier to relate each image to the uploaded file when trying to get an image to work in VPHOT. This will show exactly which file was used for each image. That way if the header needs correction I'll know exactly which image to edit. I name the images by object, date, color, if stacked, etc to help me recognize it.

Thanks,
Gary

Eric Dose
Eric Dose's picture
Transform or not; just be consistent

George had it right: if you don't transform DSLR mags, best report them as being in DSLR colors (TG, etc). By contrast, if you do transform to Johnson-Cousins, best to report them in Johnson-Cousins. This is general photometric best practice, in no way specific to VPhot.

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