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XMM-Newton Science Analysis System


selectlib (selectlib-4.68) [xmmsas_20041122_1834-6.1.0]

Meta Index / Home Page / Description / File-based filters

mask-filter

mask(x.msk,x0,y0,x,y) is true if the value of the mask image shifted by $(x0,y0)$ in the data set x.msk at the location $(x,y)$ is not equal to zero.

If the specified mask image contains the World-Coordinate-System (WCS) attributes CRPIXx, CRVALx, CDELTx with x being either 1 or 2, image coordinate values are computed from the respective integer pixel numbers $n$ as

$$r_i(n) = (n - \index{Attributes!CRPIX}{\tt CRPIX}_i) \times... ... CDELT}_i + \index{Attributes!CRVAL}{\tt CRVAL}_i,\qquad i=1,2$$ (1)

This effectively defines the pixel size in the mask image as $\index{Attributes!CDELT1}{\tt CDELT1} \times \index{Attributes!CDELT2}{\tt CDELT2}$. If symbolic names have been specified in the mask filter command as x and y and the corresponding columns in the processed table have associated WCS-attributes TCRPXx, TCRVLx, and TCDLTx respectively the actual coordinate values are calculated as above. This effectively defines the table pixel size as $\index{Attributes!TCDLT}{\tt TCDLT}x \times \index{Attributes!TCDLT}{\tt TCDLT}y$. The mask filter expression then evaluates to true for each ``table pixel'' if it has no overlap with any image mask pixel.

Mask images are ordinary rectangular arrays of any integral type supported by the dal.