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Photometry Transformation Generation Program

Please note: This page and all of its content is still under construction and subject to change. The program itself is still being tested and not ready for distribution.

The Photometry Transformation Generation Program (PTGP) was conceived and written by AAVSO member/observer Gordon Myers in response to a need for an easy-to-use program which will aid the observer in the computation of their transformation coefficients. The AAVSO acknowledges and appreciates Gordon's 100% volunteer effort.


The purpose of this program is to read an input file containing instrumental magnitudes measured of one of the standard fields (currently just M67 and NGC 7790) and from this, compute the transformation coefficients. You will be given the opportunity to plot the results, remove discrepant observations from the computation, and average together your results from multiple nights to obtain final results.


PTGP requires the use of Python 2.7 along with several helper modules. Following the procedures given below will ensure that you have all of the necessary software to run the program.

Windows Installation Procedure

This is a beta test version of the installation files for a Windows system for the Photometry Transformation Generation Program (PTGP).  It is a single file containing the required Python installation files, the PTGP program files ( and PTGP_V4.0_Python2.7.pyw), two required standard star field files (M67_Field_Magnitudes.txt and NGC7790_Field_Magnitudes.txt) and a demonstration file containing instrument magnitudes (M67_T17_20140330_Photometry_Demo_instrument_mags.txt).

It should work on Windows XP, Windows 7 and Windows 8.

Download   and extract. Then select and execute the file -   PTGP_V4.0_Windows_Setup.bat

To set up an icon for executing the program, navigate with windows explorer to c:/Python27/Photometry/PTGP_V4.0_Python2.7.pyw  (note the .pyw – NOT .py).  Right click on the file,  select Send to -> Desktop (create shortcut).  This will create a shortcut on your desktop named PTGP_V4.0_Python2.7.pyw – Shortcut.

There is a demonstration set of measurements you can use the first time you use the program.  Add the telescope name “T17″.  Then select the file named “M67_T17_20140330_Photometry_Demo_instrument_mags.txt”.  You can then generate a set of transforms and use the full program.

Mac Installation Procedure

Three separate steps are required to install the program on a Mac – (1) Install the Python 2.7 environment by downloading and installing Anaconda 1.9.1;  (2) Download six files, putting five into a user defined folder and the sixth into the Mac Applications folder.  (3) Start the PTGP program by clicking on the PTGP_v4.0 icon in the Applications Folder.

Details follow -

Anaconda V. 1.9.1 Installation:

The user should first install Anaconda version 1.9.1 which contains Python 2.7 and supporting libraries.   Download Anaconda v. 1.9.1 and install by selecting the downloaded installation package –  This installation creates a new top-level folder “/anaconda” containing all the Python software required to run PTGP.  Do the following to ensure the anaconda file is installed properly -

During install this window appears:

Select “Install on a specific disk…” -

Select Macintosh HD -

Select “Continue” to proceed.  The anaconda folder will be placed on the Macintosh HD drive as a top level folder.

The installation process will continue to completion.

This installation package supports OS X  on a 64 bit Mac.  If you have a different machine, visit   to locate other available downloads.

NOTE: Do NOT download the current Anaconda version 1.9.2.  It contains errors which make the PTGP program unusable

PTGP and Required Files Installation:

Use “Finder” to create a new folder named “Photometry”.  This folder must be a direct sub-folder of /anaconda.  (i.e., use Finder and navigate to the /anaconda folder.  Select “File -> New Folder” and type in “Photometry”)

Download   Click on the file to see its contents, and then use Finder to move the files as follows:

Move these five files to your /anaconda/Photometry folder:

  • TransformationDevelopment_V4.0_PythonV2.7.pyw
  • M67_Field_Magnitudes.txt
  • NGC7790_Field_Magnitudes.txt
  • M67_T17_20140330_Photometry_Demo_instrument_mags.txt

Move this one file to your Applications Folder –

Launch the Program:

The PTGP_V4.0 icon is in the Applications Folder.  HOLD THE CONTROL KEY DOWN THE FIRST TIME YOU CLICK ON THE PTGP_V4.0 ICON.  This will allow your computer to open the program.  Subsequent opening will not require the control key.  THE PROGRAM SOMETIMES TAKES 15 SECONDS TO START – BE PATIENT.

There is a demonstration set of measurements you can use the first time you use the program.  Add the telescope name “T17″.  Then select the file named “M67_T17_20140330_Photometry_Demo_instrument_mags.txt”.  You can then generate a set of transforms and use the full program.

User's Guide

The User's Guide is available in two formats:

PhotometryTransformationGenerationProgramUsersGuide_V4.0.pdf (479K)
PhotometryTransformationGenerationProgramUsersGuide_V4.0.docx (377K)


Gordon Myers - gordonmyers @

Copyright © 2014.

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484