Step by Step Instructions for generating Transformation Coefficients using VPhot / Transform Generator (TG) are included in this pinned post.
Vphot/TG Transformation Coefficient Generation Process – Step by Step
Task 1 – Generate Ensemble Sequence in Vphot for Use in Vphot/TG.
- It is assumed that you have collected images of an AAVSO Standard Field (e.g., M67) in multiple filters (e.g., BVRI) and uploaded them to VPhot.
- In Vphot, select/open one of your V images of an AAVSO Standard Field (e.g. M67).
- Under Catalog, click ‘Load AAVSO Standard Stars’. Many stars (e.g., 165 comps) will now have blue apertures/names identified on the image.
- On left side window in the standard star/comp list, note the list of star names all have AAVSO Unique Identifiers (AUID) (e.g., 000-BLG-879).
- Select one of these standard comps (e.g., 000-BLH-002) on the image (zoom in to see comps more easily), left click the comp, box opens, click radio button for ‘Check star’ rather than ‘Comp star’ to make this the check star. (Note that the check star is not used for generation of coefficients but is needed to meet normal analysis report protocol). Click ‘Update’ and Close.
- Select one of these standard comps (e.g., 000-BLG-956) on the image (zoom in to see comps more easily), left click the comp, box opens, click radio button for ‘Fixed Target star’ rather than ‘Comp star’ to make this the target star. (Note that the target is not used for generation of coefficients but is needed to meet normal analysis report protocol). Click ‘Update’ and Close.
- Check star will appear with orange aperture on image and in left comp list. Target star will appear with green aperture and in left comp list.
- Click blue ‘Save’ link at bottom of star list and give your saved sequence a name like ‘M67 BVRI All Std Comps 240801’.
- Do not worry about what the Image Window and Photometry Report window looks like at this point. TG will take care of removal of poor comps due to overlap, saturation, and other problems by visual observation/deactivation of poor (> 2 sigma) data points on the subsequent TG plots!
- Note: It is possible to initially/carefully delete/de-select/remove std stars from the image/sequence by zooming into the image and removing any stars from the sequence that appear overlapped, saturated, or too faint. However, in ‘most’ cases, this tedious process is not necessary since deselection within TG plots is more efficient and statistically valid. Just use ALL the standard field stars in the saved sequence.
Task 2 - Generate Instrumental Magnitude Report in Vphot for Use in TG.
- It is assumed that you now have all your AAVSO Standard Field images (e.g., M67 BVRI) listed in your VPhot ‘Available Images’ list. Check boxes to include one set of all these standard M67 images (e.g., 4 filter images) in your Available Images List (e.g., BVRI x 1 night).
- Select/click Time Series.
- Select your saved Std Field Sequence from Task 1 in the sequence pull-down box. Leave other settings as defaults.
- Click ‘Start the analysis’.
- Click ‘Continue to the result page’.
- Click ‘General Export’ on Time Series page.
- At bottom of ‘Export Time Series Results’ page, click ‘Save to AIP fmt for TG’. Save file on your computer with name like ‘M67 BVRI TG Report 240801’ and save in some folder as desired).
- Repeat Task 2 for other (e.g., 2) day’s BVRI images. This will permit the calculation of average Transformation Coefficients.
Task 3 – Generate Transformation Coefficients for use in Vphot/Transform Applier.
- Note: Look under the following link to find how to install/set up Transform Generator (TG) on your computer: Transform Generator (TG) -- (Version 6.9a) | aavso (I recommend using the Single File Installation version).
- Open Transform Generator (TG) on your computer. May take a while, be patient.
- Click in ‘Add Scope’ pull-down box, click ‘Add Scope’ again, type a ‘System Name?’ that you understand. Click ‘Enter’ to save.
- Select the M67 (or other as appropriate) radio button in ‘Select Standards Field’.
- Select TG/AIP4WIN radio button. Should be checked as default already.
- Click “Select File(s) button. Find/Select the Saved Vphot file from earlier step 17. File name will appear in ‘Current file’ box.
- Click ‘Calculate Transform Set’ button.
- List of Coefficients will appear in bottom of window.
- Click first coefficient line (i.e., Tbv). Plot opens. Expand to full screen.
- Click/select each green data point on plot that is ‘outside’ the blue 2 sigma lines. They will turn red. Continue the process as blue 2 sigma lines shrink inwards. This process WILL get to the point of diminishing returns. Do NOT overdo it! You may leave points that are on the 2 sigma lines but do not remove data points inside the 2-sigma lines. Data points near the extreme color ends of each plot are the most important in defining the Fit line.
- At the end of selection, just close the window as normal in windows. BTW, there is a tool (‘save the figure’) at bottom of screen to save the plot.
- Continue this process for ALL other listed coefficients.
- Then, click ‘Save Transform Set’. The Coefficient File is automatically saved as an *.ini file in a hidden location. Click “OK’.
- Repeat the TG process for any other day’s magnitude reports (usually ~3).
- After you have saved all the days results, click on ‘Review/Average Transform Sets’ to open all available coefficients result sets.
- Note: Report any problems with these instructions by replying in this forum topic.
- Select the results from all the image days (~3) and then click ’Retrieve transform sets’. All saved days should be listed. Check each day’s results that look reasonably similar (coeff and error).
- Click ‘Compute Average of Checked Transform Sets’. The ‘Avg Transform’ set will appear in Yellow highlight.
- Compare the day’s results to confirm reasonable consistency!
- Click ‘Save File of Average Transforms, Enter/Select File Name’. A prompt appears to input an appropriate file name to identify the target (e.g. M67 BVRI System Date of analysis). Don’t worry about the extension type. Just click Save. The file will be automatically saved as an *.ini file. This file can be opened in a text editor to view.
- This ‘average’ *.ini file can be opened/used in Vphot/TransformApplier (TA) to transform applicable AAVSO Report files!
HTH, Ken
PS: Post a reply if you have any problems with this process.