8.5. CONVENTIONAL COORDINATE TYPES

89

Table 8.8.

Example keywords for a 100 element array of complex values.

Keyword

SIMPLE

=

T

BITPIX

=

-32

NAXIS

=

2

NAXIS1

=

2

NAXIS2

=

100

CTYPE1

= 'COMPLEX'

CRVAL1

=

0.

CRPIX1

=

0.

CDELT1

=

1.

END

values and that the meaning of these integers is only defined by convention. The first

"conventional" coordinate is CTYPEi a = 'COMPLEX' to specify that complex values (i.e.,

pairs of real and imaginary components) are stored in the data array (along with an

optional weight factor). Thus, the complex axis of the data array will contain 2 values

(or 3 if the weight is specified). By convention, the real component has a coordinate

value of 1, the imaginary component has a coordinate value of 2, and the weight, if any,

has a coordinate value of 3. Table 8.8 illustrates the required keywords for an array of

100 complex values (without weights).

The second conventional coordinate is CTYPEi a = 'STOKES' to specify the polar-

ization of the data. Conventional values, their symbols, and polarizations are given in

Table 8.9.

FITS Standard