The extension header keyword
MAXIS (integer) gives the number of dimensions of the array in the table field.
The properties of the array would be given in columns in the table. The column labels would be the names of the keywords used to describe a primary or image data array, except that NAXISn would be replaced by MAXISm. These labels are given by the values of the TTYPEn keywords in the binary table header. Thus,
Because the array field must be the same size in all rows, the values of the MAXISm will usually be the same for all rows of the table, and they can then be given as header keywords instead of table columns:
MAXISm,m=1,...,MAXIS (integer) gives the number of elements along axis m in the array contained in the table.
It is possible for array to have the same size in two rows but different numbers of elements along the axes, for example 36 × 6 in one row and 24 × 9 in another. In that case, the number of elements along each axis must be given in a table column.
One field - call it k - will contain the actual data array. For this row, two keyword-value pairs are required:
TFORMk = 'DATA '
TMATXk = T
A value of F is understood for the TMATXm keyword for all other columns and need not be included explicitly.
It is possible to combine this convention with the use of the TDIMn keyword proposed in the binary table paper by setting
TDIMk = '(MAXIS1,MAXIS2,...)'
where the MAXISm represent the number of elements along axis m that would otherwise be the values of the MAXISm keywords. The CLASS package for analysis of radio astronomical data supports the Green Bank convention.