Calibration Access and Data Handbook

Generation from Ground Calibration Data

The distortion was first derived from CSL pinhole measurements. Double pinholes were excluded from this analysis. The pinhole positions were scaled, rotated and shifted until the best match between pinhole position and measured image was achieved. A pinhole starmask image in the correct position was generated (starmask_new.fits). The adopted parameters were:

rotation angle	=	62$^{\circ}$ clockwise
xshift	=	196 -0.41669 pixels
yshift	=	-34 -0.08849 pixels

The platescale was assumed as 0.499844 arcsec/pixel in the generation of the pinhole image, which is based on the following measurements on the OM FM:

Pixel Size	=	9.2675x10-4 cm
Focal Length	=	382.431 cm

Pinholes starmask positions and centroids of the measured images were paired, and the difference between measured and expected positions is written to a file (routine DISTORT.PRO). Finally the offsets are parameterized as function of field position, more precisely as function of the distance to the boresight position, i.e. (x-1024.5). The offsets were fitted with an up to 7th order polynomial (cf. section 3.5.5) using the routine DISTORT_FORM.PRO
The analysis was performed by Alice Breeveld (MSSL).