fitsinfo

Return information about a FITS file

Syntax

• S = fitsinfo(filename)
  

Description

S = fitsinfo(filename) returns a structure whose fields contain information about the contents of a Flexible Image Transport System (FITS) file. filename is a string that specifies the name of the FITS file.

The structure, S, obtained from a basic FITS file, contains the following fields.

Information Returned From a Basic FITS File

Fieldname	Description	Return Type
Contents	List of extensions in the file in the order that they occur	Cell array of Strings
FileModDate	File modification date	String
Filename	Name of the file	String
FileSize	Size of the file in bytes	Double
PrimaryData	Information about the primary data in the FITS file	Structure array

A FITS file may also include any number of extensions. For such files, fitsinfo returns a structure, S, with the fields listed above plus one or more of the following structure arrays.

Additional Information Returned From FITS Extensions

Fieldname	Description	Return Type
AsciiTable	ASCII Table extensions	Structure array
BinaryTable	Binary Table extensions	Structure array
Image	Image extensions	Structure array
Unknown	Nonstandard extensions	Structure array

The tables that follow show the fields of each of the structure arrays that can be returned by fitsinfo.

Note For all Intercept and Slope fieldnames below, the equation used to calculate actual values is, actual_value = (Slope * array_value) + Intercept.

Fields of the PrimaryData Structure Array

Fieldname	Description	Return Type
DataSize	Size of the primary data in bytes	Double
DataType	Precision of the data	String
Intercept	Value, used with Slope, to calculate actual pixel values from the array pixel values	Double
Keywords	Keywords, values and comments of the header in each column	Cell array of strings
MissingDataValue	Value used to represent undefined data	Double
Offset	Number of bytes from beginning of the file to the first data value	Double
Size	Sizes of each dimension	Double array
Slope	Value, used along with Intercept, to calculate actual pixel values from the array pixel values	Double

Fields of the AsciiTable Structure Array

Fieldname	Description	Return Type
DataSize	Size of the data in the ASCII Table in bytes	Double
FieldFormat	Formats in which each field is encoded, using FORTRAN-77 format codes	Cell array of strings
FieldPos	Starting column for each field	Double array
FieldPrecision	Precision in which the values in each field are stored	Cell array of strings
FieldWidth	Number of characters in each field	Double array
Intercept	Values, used along with Slope, to calculate actual data values from the array data values	Double array
Keywords	Keywords, values and comments in the ASCII table header	Cell array of strings
MissingDataValue	Representation of undefined data in each field	Cell array of strings
NFields	Number of fields in each row	Double array
Offset	Number of bytes from beginning of the file to the first data value	Double
Rows	Number of rows in the table	Double
RowSize	Number of characters in each row	Double
Slope	Values, used with Intercept, to calculate actual data values from the array data values	Double array

Fields of the BinaryTable Structure Array

Fieldname	Description	Return Type
DataSize	Size of the data in the Binary Table, in bytes. Includes any data past the main part of the Binary Table.	Double
ExtensionOffset	Number of bytes from the beginning of the file to any data past the main part of the Binary Table	Double
ExtensionSize	Size of any data past the main part of the Binary Table, in bytes	Double
FieldFormat	Data type for each field, using FITS binary table format codes	Cell array of strings
FieldPrecision	Precisions in which the values in each field are stored	Cell array of strings
FieldSize	Number of values in each field	Double array
Intercept	Values, used along with Slope, to calculate actual data values from the array data values	Double array
Keywords	Keywords, values and comments in the Binary Table header	Cell array of strings
MissingDataValue	Representation of undefined data in each field	Cell array of double
NFields	Number of fields in each row	Double
Offset	Number of bytes from beginning of the file to the first data value	Double
Rows	Number of rows in the table	Double
RowSize	Number of bytes in each row	Double
Slope	Values, used with Intercept, to calculate actual data values from the array data values	Double array

Fields of the Image Structure Array

Fieldname	Description	Return Type
DataSize	Size of the data in the Image extension in bytes	Double
DataType	Precision of the data	String
Intercept	Value, used along with Slope, to calculate actual pixel values from the array pixel values	Double
Keywords	Keywords, values and comments in the Image header	Cell array of strings
MissingDataValue	Representation of undefined data	Double
Offset	Number of bytes from the beginning of the file to the first data value	Double
Size	Sizes of each dimension	Double array
Slope	Value, used along with Intercept, to calculate actual pixel values from the array pixel values	Double

Fields of the Unknown Structure Array

Fieldname	Description	Return Type
DataSize	Size of the data in nonstandard extensions, in bytes	Double
DataType	Precision of the data	String
Intercept	Value, used along with Slope, to calculate actual data values from the array data values	Double
Keywords	Keywords, values and comments in the extension header	Cell array of strings
MissingDataValue	Representation of undefined data	Double
Offset	Number of bytes from beginning of the file to the first data value	Double
Size	Sizes of each dimension	Double array
Slope	Value, used along with Intercept, to calculate actual data values from the array data values	Double

Example

Use fitsinfo to obtain information about FITS file, tst0012.fits. In addition to its primary data, the file also contains three extensions: Binary Table, Image, and ASCII Table.

• S = fitsinfo('tst0012.fits');
  S =
         Filename: 'tst0012.fits'
      FileModDate: '27-Nov-2000 13:25:55'
         FileSize: 109440
         Contents: {'Primary'  'Binary Table'  'Image'  'ASCII'}
      PrimaryData: [1x1 struct]
      BinaryTable: [1x1 struct]
            Image: [1x1 struct]
       AsciiTable: [1x1 struct]
  

The PrimaryData substructure shows that the data resides in a 102-by-109 matrix of single-precision values. There are 44,472 bytes of primary data starting at an offset of 2,880 bytes from the start of the file.

• S.PrimaryData
  ans =
              DataType: 'single'
                  Size: [102 109]
              DataSize: 44472
      MissingDataValue: []
             Intercept: 0
                 Slope: 1
                Offset: 2880
              Keywords: {25x3 cell}
  

Examining the ASCII Table substructure, you can see that this table has 53 rows, 59 columns, and contains 8 fields per row. The last field in each row, for example, begins in the 55th column and contains a 4-digit integer.

• S.AsciiTable
  ans =
                  Rows: 53
               RowSize: 59
               NFields: 8
           FieldFormat: {1x8 cell}
        FieldPrecision: {1x8 cell}
            FieldWidth: [9 6.2000 3 10.4000 20.1500 5 1 4]
              FieldPos: [1 11 18 22 33 54 54 55]
              DataSize: 3127
      MissingDataValue: {'*'  '---.--'  '*'  []  '*'  '*'  '*'  ''}
             Intercept: [0 0 -70.2000 0 0 0 0 0]
                 Slope: [1 1 2.1000 1 1 1 1 1]
                Offset: 103680
              Keywords: {65x3 cell}
  
  S.AsciiTable.FieldFormat
  ans =
      'A9'   'F6.2'   'I3'   'E10.4'   'D20.15'   'A5'   'A1'   'I4'
  

The ASCII Table includes 65 keyword entries arranged in a 65-by-3 cell array.

• key = S.AsciiTable.Keywords
  
  key =
  S.AsciiTable.Keywords
  ans =
      'XTENSION'    'TABLE'         [1x48 char]
      'BITPIX'      [         8]    [1x48 char]
      'NAXIS'       [         2]    [1x48 char]
      'NAXIS1'      [        59]    [1x48 char]
          .             .                .
          .             .                .
          .             .                .
  

One of the entries in this cell array is shown here. Each row of the array contains a keyword, its value, and comment.

• key{2,:}
  
  ans =
  BITPIX                              % Keyword
  
  ans =
       8                              % Keyword value
  
  ans =
   Character data 8 bits per pixel    % Keyword comment