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        The format for the input file consits of a four line header as such:
    1st line : NX XREF XVAL XINC
    2nd line : (any comment for first axis, could be blank)
    3rd line : NY YREF YVAL YINC
    4th line : (any comment for 2nd axis, could be blank)
    followed by the data (NX times NY pixel values) in a format which can be
    specified with the /FORMAT option when the default 10z8 is not used.
    NX is the number of pixels in the 1st dimension of the map  (on  the  "X
    axis"), XREF the index of the pixel for which the actual X abscissa val-
    ue is XVAL, the increment between two pixels being XINC,  and  the  same
    for  the  y  axis.  Thus,  the  abcissa X of the pixel 'I' is just X=(I-
    This format is very simple-minded (so that any inexperienced  programmer
    can use it in less than 5 minutes), but highly non efficient in I/O pro-
    cessing. A more elaborate data format ("IMAGES"), specially  suited  for
    astronomical  applications  and  large  maps is available through GREG3\
    language (command GREG3\IMAGE), or directly using SIC variables (command
    SIC\DEFINE)  and  the  /VARIABLE option of this command. One should read
    once its data in RGDATA format in GreG, then convert it for  future  use
    in IMAGE format with the command GREG2\WRITE IMAGE filename.

    See also the IMAGE_HOWTO subtopic of the GREG2\PLOT command.

Gildas manager 2014-07-01