The FITS handler,
FitsTableWriter
,
will output a FITS file with N+1 HDUs for N tables; the first
(primary) HDU has no interesting content, and subsequent ones
(the extensions) are of type BINTABLE, one for each output table.
A variant handler,
VariableFitsTableWriter
is also provided. This behaves in much the same way,
but in the case of columns which contain variable-shaped arrays
(ones for which the last element of ColumnInfo.getShape() is negative)
it will store the array data in the 'heap' following the table data
in the BINTABLE HDU, using the 'P' or 'Q' data type specifiers in the
relevant TFORMn header cards.
To write the FITS header for the table extension, certain things
need to be known which may not be available from the StarTable
object being written; in particular the number of rows and the
size of any variable-sized arrays (including variable-length strings)
in the table. This may necessitate two passes through the data to
do the write.
To fix the value of the TNULLn
magic value for
a given column on output, set the value of the
Tables.NULL_VALUE_INFO
auxiliary metadata value, e.g.:
colInfo.setAuxDatum(new DescribedValue(Tables.NULL_VALUE_INFO, new Integer(-99)));
Writing columns containing (scalar or array) unsigned byte values
(TFORMnn = 'B'
) cannot be done simply by providing
byte
data to write, since the java byte type is signed.
To do it, you must provide a column of java short
(16-bit) integers, and set the value of the
Tables.UBYTE_FLAG_INFO
auxiliary metadata item to Boolean.TRUE
, e.g.:
colInfo.setAuxDatum(new DescribedValue(Tables.UBYTE_FLAG_INFO, Boolean.TRUE));
Writing columns containing (scalar or array) unsigned long values
cannot be done straightforwardly, since, like FITS, the Java long
type is signed.
Instead, you can provide a column of java String
values
giving the integer representation of the numbers required,
and set the value of the
BintableStarTable.LONGOFF_INFO
auxiliary metadata item to the string representation of the offset 2**63,
e.g.:
colInfo.setAuxDatum(new DescribedValue(BintableStarTable.LONGOFF_INFO, "9223372036854775808263"));This will result in the values being written, where in range, with FITS headers
TFORMnn = 'K'
, TZEROnn = '9223372036854775808263'
.
The same mechanism can be used for other long offsets if required
(though not for other integer types).
See the "Binary Table Extension" section of the FITS standard for more details of the FITS BINTABLE format. This handler can write tables with more than the BINTABLE limit of 999 columns, as discussed in Section 3.8.1.
There is some support for the semi-standard
HEALPix-FITS
serialization convention.
If some of the HPX_*_INFO
metadata items defined by the class
HealpixTableInfo
are present
in the output table's parameter list,
the corresponding HEALPix-specific FITS headers will be written
on a best-efforts basis into the output BINTABLE HDU.
This may or may not be good enough to make that FITS file readable by
external HEALPix-FITS-aware applications; one of the requirements
of the convention is that the HEALPix pixel index, if present,
appears in the first column of the table under the name "PIXEL
".
An alternative is to use the handler
HealpixFitsTableWriter
,
which tries harder to write tables using the HEALPix convention.
This will fail unless the required HPX_*_INFO
metadata
items mentioned above are present, and will reorder and rename
columns as required for maximum compatibility.
StarTableOutput
will write in FITS format
(using the default handler)
format string "fits" is used, or the format string is null and
the destination string ends in ".fits".