There are twelve extension - one for each filter - named FILTER-FilterId. Two extensions are required for each grism to describe the displacement of the zero orders with respect to the direct image obtained with the lenticular filters.

Two additional extensions contain the polynomial coefficients describing the distortion for all the filters.

FILTER-U |

FILTER-B |

FILTER-V |

FILTER-UVW1 |

FILTER-UVM2 |

FILTER-UVW2 |

FILTER-WHITE |

FILTER-MAGNI |

FILTER-GRISM1 |

FILTER-GRISM2 |

FILTER-GRISM10 |

FILTER-GRISM20 |

POLYNOM_MAP |

POLYNOM_MAP2 |

Each extension FILTER-FilterId holds a binary table sampling the detector distortion of a specific filter at a coarse resolution ( 1 datapoint every 25 subpixel). Intermediate detector position have to be obtained by interpolation. The distortion at the position RAWX, RAWY is described as the difference between the measured image position on the detector and the position assuming a linear grid. The platescale of the linear grid is the value of the keyword PLTSCALE (units: arcsec/pixel). The format of the binary tables follows the description of the CCF ICD [5].

The distortion can alternatively be obtained using two polynomials describing the offset in x- and y-direction. Analysis of calibration data showed that the detector distortion can be parameterized with an up to 7th order polynomial. The 36 parameters , ..., (cf. section 3.5.5) needed to calculate the distortion in x- and y-direction at any detector position (equivalent to RAWX_OFF and RAWY_OFF) are stored in the columns XPOLYCOEF, YPOLYCOEF of the extension POLYNOM_MAP. There is one set of coefficients per filter element in the POLYNOM_MAP extension. The filter element is found in the column FILTER_ID. The required binary table entry is identified by matching the value of the column FILTER_ID with the State Variable FilterID. The reverse transformation from distorted to flat image is available from the polynomial stored in the extension POLYNOM_MAP2. This has an identical format to the POLYNOM_MAP block.

The format of the AstroMet file is as follows

**Binary table:** FILTER-FilterID

Twelve binary extensions, one per FilterID

**Binary table:** POLYNOM_MAP

column name | column type | column unit | comment |

FILTER_ID | 9A | not applicable | filter ID |

PLTSCALE | E | arcsec/subpixel | platescale of filter specified in FILTER_ID |

XPOLYCOEF | 36E | not applicable | coefficients of x-distortion polynomial |

in ascending order | |||

YPOLYCOEF | 36E | not applicable | coefficients of y-distortion polynomial |

in ascending order |

**Binary table:** POLYNOM_MAP2

column name | column type | column unit | comment |

FILTER_ID | 9A | not applicable | filter ID |

PLTSCALE | E | arcsec/subpixel | platescale of filter specified in FILTER_ID |

XPOLYCOEF | 36E | not applicable | coefficients of x-distortion polynomial |

in ascending order | |||

YPOLYCOEF | 36E | not applicable | coefficients of y-distortion polynomial |

in ascending order |