# Photometric Systems Transformation Table

Definition of a FITS table providing the transformation between photometric systems.

The table is created by `munipack phfotran` action and used by `phcal` action.

This specification has been developed for internal use in Munipack and backward compatibility is not guarantied.

## File Structure

The file has first HDU dummy without any machine-readable information and just a short description and reference in comments.

FITS file structure
HDU | EXTNAME | Description
--- | --- | ---
0 |  | Dummy
1 | FOTRAN | The transformation table

The second HDU is a table with the transformation matrix. EXTNAME is set to FOTRAN. The header contains identifiers of input (instrumental) and output (standard) photometry systems in keywords PHOTSYS1 and PHOTSYS2. Amount of both columns and rows will generally variable and non-equal.

FOTRAN extension keywords
Keyword | Value | Description
--- | --- | ---
EXTNAME | FOTRAN | mandatory extension identifier
PHOTSYS1 |  | instrumental photometry system
PHOTSYS2 |  | standard photometry system
FILTERi |  | i-th standard filter

Columns of the table are named as instrumental filters. Rows are equivalent filters. Lets elements of tables are Ci,j than the values in the standard system (PHOTSYS2) are derived from the instrumental system (PHOTSYS1) as

c'i = Σj Cij cj

where i,j = { B,V ...} points on all available filters.

Photometric System Transformation HDU Table
Column | Type | Description
--- | --- | ---
FILTER | 12A | Filter designation
Ci1 | D | a coefficient
Ci2 | D | a coefficient
.. | D | a coefficient
Cij | D | a coefficient
.. | D | a coefficient
CiN | D | a coefficient

The table can be created by hand, but the structure must be respected and all identifiers included.

## See Also

Photometric System Transformation, Photometric Calibration