next up previous contents FITSIO Home
Next: 6.8 Row Selection and Up: 6.7 FITS ASCII and Previous: 6.7.3 Edit Rows or   Contents


6.7.4 Read and Write Column Data Routines

These subroutines put or get data values in the current ASCII or Binary table extension. Automatic data type conversion is performed for numerical data types (B,I,J,E,D) if the data type of the column (defined by the TFORM keyword) differs from the data type of the calling subroutine. The data values are also scaled by the TSCALn and TZEROn header values as they are being written to or read from the FITS array. The fttscl subroutine MUST be used to define the scaling parameters when writing data to the table or to override the default scaling values given in the header when reading from the table. Note that it is *not* necessary to insert rows in a table before writing data to those rows (indeed, it would be inefficient to do so). Instead, one may simply write data to any row of the table, whether that row of data already exists or not.

In the case of binary tables with vector elements, the 'felem' parameter defines the starting pixel within the element vector. This parameter is ignored with ASCII tables. Similarly, in the case of binary tables the 'nelements' parameter specifies the total number of vector values read or written (continuing on subsequent rows if required) and not the number of table elements. Two sets of subroutines are provided to get the column data which differ in the way undefined pixels are handled. The first set of routines (FTGCV) simply return an array of data elements in which undefined pixels are set equal to a value specified by the user in the 'nullval' parameter. An additional feature of these subroutines is that if the user sets nullval = 0, then no checks for undefined pixels will be performed, thus increasing the speed of the program. The second set of routines (FTGCF) returns the data element array and in addition a logical array of flags which defines whether the corresponding data pixel is undefined.

Any column, regardless of it's intrinsic datatype, may be read as a string. It should be noted however that reading a numeric column as a string is 10 - 100 times slower than reading the same column as a number due to the large overhead in constructing the formatted strings. The display format of the returned strings will be determined by the TDISPn keyword, if it exists, otherwise by the datatype of the column. The length of the returned strings can be determined with the ftgcdw routine. The following TDISPn display formats are currently supported:

    Iw.m   Integer
    Ow.m   Octal integer
    Zw.m   Hexadecimal integer
    Fw.d   Fixed floating point
    Ew.d   Exponential floating point
    Dw.d   Exponential floating point
    Gw.d   General; uses Fw.d if significance not lost, else Ew.d
where w is the width in characters of the displayed values, m is the minimum number of digits displayed, and d is the number of digits to the right of the decimal. The .m field is optional.

1
Put elements into an ASCII or binary table column (in the CDU). (The SPP FSPCLS routine has an additional integer argument after the VALUES character string which specifies the size of the 1st dimension of this 2-D CHAR array).

The alternate version of these routines, whose names end in 'LL' after the datatype character, support large tables with more then 2*31 rows. When calling these routines, the frow and felem parameters *must* be 64-bit integer*8 variables, instead of normal 4-byte integers.

        FTPCL[SLBIJKEDCM](unit,colnum,frow,felem,nelements,values, > status)
        FTPCL[LBIJKEDCM]LL(unit,colnum,frow,felem,nelements,values, > status)

2
Put elements into an ASCII or binary table column (in the CDU) substituting the appropriate FITS null value for any elements that are equal to NULLVAL. For ASCII TABLE extensions, the null value defined by the previous call to FTSNUL will be substituted; For integer FITS columns, in a binary table the null value defined by the previous call to FTTNUL will be substituted; For floating point FITS columns a special IEEE NaN (Not-a-Number) value will be substituted.

The alternate version of these routines, whose names end in 'LL' after the datatype character, support large tables with more then 2*31 rows. When calling these routines, the frow and felem parameters *must* be 64-bit integer*8 variables, instead of normal 4-byte integers.

        FTPCN[SBIJKED](unit,colnum,frow,felem,nelements,values,nullval > status)
        FTPCN[SBIJKED]LL(unit,colnum,(I*8) frow,(I*8) felem,nelements,values,
	                nullval > status)

3
Put bit values into a binary byte ('B') or bit ('X') table column (in the CDU). LRAY is an array of logical values corresponding to the sequence of bits to be written. If LRAY is true then the corresponding bit is set to 1, otherwise the bit is set to 0. Note that in the case of 'X' columns, FITSIO will write to all 8 bits of each byte whether they are formally valid or not. Thus if the column is defined as '4X', and one calls FTPCLX with fbit=1 and nbit=8, then all 8 bits will be written into the first byte (as opposed to writing the first 4 bits into the first row and then the next 4 bits into the next row), even though the last 4 bits of each byte are formally not defined.

        FTPCLX(unit,colnum,frow,fbit,nbit,lray, > status)

4
Set table elements in a column as undefined

        FTPCLU(unit,colnum,frow,felem,nelements, > status)

5
Get elements from an ASCII or binary table column (in the CDU). These routines return the values of the table column array elements. Undefined array elements will be returned with a value = nullval, unless nullval = 0 (or = ' ' for ftgcvs) in which case no checking for undefined values will be performed. The ANYF parameter is set to true if any of the returned elements are undefined. (Note: the ftgcl routine simple gets an array of logical data values without any checks for undefined values; use the ftgcfl routine to check for undefined logical elements). (The SPP FSGCVS routine has an additional integer argument after the VALUES character string which specifies the size of the 1st dimension of this 2-D CHAR array).

The alternate version of these routines, whose names end in 'LL' after the datatype character, support large tables with more then 2*31 rows. When calling these routines, the frow and felem parameters *must* be 64-bit integer*8 variables, instead of normal 4-byte integers.

        FTGCL(unit,colnum,frow,felem,nelements, > values,status)
        FTGCV[SBIJKEDCM](unit,colnum,frow,felem,nelements,nullval, >
                       values,anyf,status)
        FTGCV[BIJKEDCM]LL(unit,colnum,(I*8) frow, (I*8) felem, nelements,
	               nullval, > values,anyf,status)

6
Get elements and null flags from an ASCII or binary table column (in the CHDU). These routines return the values of the table column array elements. Any undefined array elements will have the corresponding flagvals element set equal to .TRUE. The ANYF parameter is set to true if any of the returned elements are undefined. (The SPP FSGCFS routine has an additional integer argument after the VALUES character string which specifies the size of the 1st dimension of this 2-D CHAR array).

The alternate version of these routines, whose names end in 'LL' after the datatype character, support large tables with more then 2*31 rows. When calling these routines, the frow and felem parameters *must* be 64-bit integer*8 variables, instead of normal 4-byte integers.

        FTGCF[SLBIJKEDCM](unit,colnum,frow,felem,nelements, >
                         values,flagvals,anyf,status)
        FTGCF[BIJKED]LL(unit,colnum, (I*8) frow, (I*8) felem,nelements, >
                         values,flagvals,anyf,status)

7
Get an arbitrary data subsection from an N-dimensional array in a binary table vector column. Undefined pixels in the array will be set equal to the value of 'nullval', unless nullval=0 in which case no testing for undefined pixels will be performed. The first and last rows in the table to be read are specified by fpixels(naxis+1) and lpixels(naxis+1), and hence are treated as the next higher dimension of the FITS N-dimensional array. The INCS parameter specifies the sampling interval in each dimension between the data elements that will be returned.

        FTGSV[BIJKED](unit,colnum,naxis,naxes,fpixels,lpixels,incs,nullval, >
                     array,anyf,status)

8
Get an arbitrary data subsection from an N-dimensional array in a binary table vector column. Any Undefined pixels in the array will have the corresponding 'flagvals' element set equal to .TRUE. The first and last rows in the table to be read are specified by fpixels(naxis+1) and lpixels(naxis+1), and hence are treated as the next higher dimension of the FITS N-dimensional array. The INCS parameter specifies the sampling interval in each dimension between the data elements that will be returned.

        FTGSF[BIJKED](unit,colnum,naxis,naxes,fpixels,lpixels,incs, >
                     array,flagvals,anyf,status)

9
Get bit values from a byte ('B') or bit (`X`) table column (in the CDU). LRAY is an array of logical values corresponding to the sequence of bits to be read. If LRAY is true then the corresponding bit was set to 1, otherwise the bit was set to 0. Note that in the case of 'X' columns, FITSIO will read all 8 bits of each byte whether they are formally valid or not. Thus if the column is defined as '4X', and one calls FTGCX with fbit=1 and nbit=8, then all 8 bits will be read from the first byte (as opposed to reading the first 4 bits from the first row and then the first 4 bits from the next row), even though the last 4 bits of each byte are formally not defined.

        FTGCX(unit,colnum,frow,fbit,nbit, > lray,status)

10
Read any consecutive set of bits from an 'X' or 'B' column and interpret them as an unsigned n-bit integer. NBIT must be less than or equal to 16 when calling FTGCXI, and less than or equal to 32 when calling FTGCXJ; there is no limit on the value of NBIT for FTGCXD, but the returned double precision value only has 48 bits of precision on most 32-bit word machines. The NBITS bits are interpreted as an unsigned integer unless NBITS = 16 (in FTGCXI) or 32 (in FTGCXJ) in which case the string of bits are interpreted as 16-bit or 32-bit 2's complement signed integers. If NROWS is greater than 1 then the same set of bits will be read from sequential rows in the table starting with row FROW. Note that the numbering convention used here for the FBIT parameter adopts 1 for the first element of the vector of bits; this is the Most Significant Bit of the integer value.

        FTGCX[IJD](unit,colnum,frow,nrows,fbit,nbit, > array,status)

11
Get the descriptor for a variable length column in a binary table. The descriptor consists of 2 integer parameters: the number of elements in the array and the starting offset relative to the start of the heap. The first routine returns a single descriptor whereas the second routine returns the descriptors for a range of rows in the table.

        FTGDES(unit,colnum,rownum, > nelements,offset,status)
        FTGDESLL(unit,colnum,rownum, > nelementsll,offsetll,status)

        FTGDESS(unit,colnum,firstrow,nrows > nelements,offset, status)
        FTGDESSLL(unit,colnum,firstrow,nrows > nelementsll,offsetll, status)

12
Write the descriptor for a variable length column in a binary table. These subroutines can be used in conjunction with FTGDES to enable 2 or more arrays to point to the same storage location to save storage space if the arrays are identical.

        FTPDES(unit,colnum,rownum,nelements,offset, > status)
        FTPDESLL(unit,colnum,rownum,nelementsll,offsetll, > status)


next up previous contents FITSIO Home
Next: 6.8 Row Selection and Up: 6.7 FITS ASCII and Previous: 6.7.3 Edit Rows or   Contents