XMM-Newton Science Analysis System


selectlib (selectlib-4.77) [xmmsas_20230412_1735-21.0.0]

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

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