Class FitsConstants

java.lang.Object
uk.ac.starlink.oldfits.FitsConstants

public class FitsConstants extends Object
Utility class providing some constants and static methods related to FITS file format and starlink classes.
Author:
Mark Taylor (Starlink)
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final nom.tam.fits.HeaderCard
    Image of end-of-header card.
    static final int
    Standard size of a FITS block in bytes.
    static final int
    Maximum number of columns in standard FITS BINTABLE extension.
    static final String
    FITS header card for indicating NDArray origin values.
    static final String
    Prefix for NDArray-related FITS header cards.
    static final String
    Prefix for NDX-related FITS header cards.
    static final String
    FITS header card for location (relative URL) of XML representation.
    static boolean
    Whether HIERARCH convention is used; true by default.
    static final String
    Default encoding used for writing WCS into FITS headers.
  • Constructor Summary

    Constructors
    Constructor
    Description
     
  • Method Summary

    Modifier and Type
    Method
    Description
    static void
    addStringValue(nom.tam.fits.Header hdr, String key, String value, String comment)
    Attempts to add a string-valued card to the header.
    static void
    addTrimmedValue(nom.tam.fits.Header hdr, String key, String value, String comment)
    Adds a string-valued card to the header.
    static nom.tam.fits.HeaderCard
    Create a HeaderCard from a FITS card image.
    static nom.tam.fits.HeaderCard
    createRawHeaderCard(String keyname, String rawvalue, String comment)
    Create a header card given the final representation of the card value.
    static nom.tam.fits.Header
    Creates a Header instance which does not perform any unsolicited reordering of the header cards.
    static List<String>
    Gets the default permitted list of extensions which identify a FITS resource in the path part of a URL.
    static long
    getDataSize(nom.tam.fits.Header hdr)
    Utility function to find the number of bytes in the data segment of an HDU.
    static nom.tam.util.ArrayDataInput
    getInputStreamStart(uk.ac.starlink.util.DataSource datsrc)
    Returns an input stream which can be used with the various FITS classes based on a given DataSource object, positioned at the start of the stream.
    static Iterable<nom.tam.fits.HeaderCard>
    headerIterable(nom.tam.fits.Header hdr)
    Returns an iterable over HeaderCards for a given Header.
    static boolean
    isMagic(byte[] buffer)
    Indicates whether the supplied buffer is the start of a FITS file.
    static int
    readHeader(nom.tam.fits.Header hdr, nom.tam.util.ArrayDataInput strm)
    Populates a header from an input stream, reporting its length in bytes.
    static long
    skipHDUs(nom.tam.util.ArrayDataInput stream, int nskip)
    Skips forward over a given number of HDUs in the supplied stream.
    static void
    Writes a null header representing an empty primary HDU to a stream.
    static void
    writeHeader(DataOutput strm, nom.tam.fits.Header hdr)
    Writes a header object to a DataOutput.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • NDARRAY_PREFIX

      public static final String NDARRAY_PREFIX
      Prefix for NDArray-related FITS header cards.
      See Also:
    • END_CARD

      public static final nom.tam.fits.HeaderCard END_CARD
      Image of end-of-header card.
    • NDARRAY_ORIGIN

      public static final String NDARRAY_ORIGIN
      FITS header card for indicating NDArray origin values. An integer (1, 2, ... ) is appended to this value for the different axes like for NAXIS.
      See Also:
    • NDX_PREFIX

      public static final String NDX_PREFIX
      Prefix for NDX-related FITS header cards.
      See Also:
    • NDX_XML

      public static final String NDX_XML
      FITS header card for location (relative URL) of XML representation.
      See Also:
    • WCS_ENCODING

      public static final String WCS_ENCODING
      Default encoding used for writing WCS into FITS headers.
      See Also:
    • FITS_BLOCK

      public static final int FITS_BLOCK
      Standard size of a FITS block in bytes.
      See Also:
    • MAX_NCOLSTD

      public static final int MAX_NCOLSTD
      Maximum number of columns in standard FITS BINTABLE extension.
      See Also:
    • REQUIRE_HIERARCH

      public static boolean REQUIRE_HIERARCH
      Whether HIERARCH convention is used; true by default.
  • Constructor Details

    • FitsConstants

      public FitsConstants()
  • Method Details

    • defaultFitsExtensions

      public static List<String> defaultFitsExtensions()
      Gets the default permitted list of extensions which identify a FITS resource in the path part of a URL.
      Returns:
      unmodifiable list of default FITS extensions - ".fits", ".fit" etc
    • createUnsortedHeader

      public static nom.tam.fits.Header createUnsortedHeader()
      Creates a Header instance which does not perform any unsolicited reordering of the header cards. Some versions of nom.tam.fits force the EXTEND keyword to go directly after the NAXISn keywords. That screws up specification of the FITS-plus magic number, which is expected to have VOTMETA directly after NAXISn. Headers created using this method will leave header cards in the order they are added.
      Returns:
      new empty header
      See Also:
    • createHeaderCard

      public static nom.tam.fits.HeaderCard createHeaderCard(String cardImage)
      Create a HeaderCard from a FITS card image.
      Parameters:
      cardImage - the 80 character card image
      Returns:
      card object
    • createRawHeaderCard

      public static nom.tam.fits.HeaderCard createRawHeaderCard(String keyname, String rawvalue, String comment) throws nom.tam.fits.HeaderCardException
      Create a header card given the final representation of the card value. No additional manipulation will be done on the value; for instance it will not be wrapped in quotes. Use this method with caution, since the arguments may not be checked as rigorously as during normal header creation, though steps will be taken to ensure that the header does not overflow the 80 character limit.
      Parameters:
      keyname - header card name
      rawvalue - raw header card value
      comment - comment text (ignored if too long)
      Returns:
      new header card
      Throws:
      nom.tam.fits.HeaderCardException - if card would be too long
    • headerIterable

      public static Iterable<nom.tam.fits.HeaderCard> headerIterable(nom.tam.fits.Header hdr)
      Returns an iterable over HeaderCards for a given Header.
      Parameters:
      hdr - header
      Returns:
      iterable over hdr's cards
    • skipHDUs

      public static long skipHDUs(nom.tam.util.ArrayDataInput stream, int nskip) throws IOException
      Skips forward over a given number of HDUs in the supplied stream. If it reaches the end of the stream, it throws an IOException with a Cause of a TruncatedFileException.
      Parameters:
      stream - the stream to skip through
      nskip - the number of HDUs to skip
      Returns:
      the number of bytes the stream was advanced
      Throws:
      IOException
    • isMagic

      public static boolean isMagic(byte[] buffer)
      Indicates whether the supplied buffer is the start of a FITS file. Its contents is checked against the FITS 'magic number', which is the ASCII string "SIMPLE  =".
      Parameters:
      buffer - a byte buffer containing the start of a file to test
      Returns:
      true iff the bytes in buffer look like the start of a FITS file
    • getInputStreamStart

      public static nom.tam.util.ArrayDataInput getInputStreamStart(uk.ac.starlink.util.DataSource datsrc) throws IOException
      Returns an input stream which can be used with the various FITS classes based on a given DataSource object, positioned at the start of the stream.
      Parameters:
      datsrc - the DataSource pointing to the file/HDU required
      Returns:
      an ArrayDataInput acquired from datsrc,
      Throws:
      IOException
    • readHeader

      public static int readHeader(nom.tam.fits.Header hdr, nom.tam.util.ArrayDataInput strm) throws nom.tam.fits.TruncatedFileException, IOException
      Populates a header from an input stream, reporting its length in bytes. This does the same as Header.read(nom.tam.util.ArrayDataInput), but it returns the number of bytes read from the input stream in order to populate the header (including any padding bytes). There is no way to retrieve this information from the Header class in general; though Header.getSize() will sometimes give you the right answer, in the case of duplicated header keywords it can give an underestimate. This could be seen as a bug in nom.tam.fits classes, but there may be code somewhere which relies on that behaviour.

      You can make a Header from scratch by doing

           Header hdr = new Header();
           int headsize = read( hdr, strm );
       
      This method also differs from the Header implementation in that it does not print warnings to standard output about duplicate keywords.
      Parameters:
      hdr - the header to populate
      strm - the input stream supplying the data
      Returns:
      the number of bytes in the FITS blocks which comprise the header content
      Throws:
      nom.tam.fits.TruncatedFileException
      IOException
      See Also:
      • Header.read(nom.tam.util.ArrayDataInput)
    • writeHeader

      public static void writeHeader(DataOutput strm, nom.tam.fits.Header hdr) throws IOException
      Writes a header object to a DataOutput.
      Parameters:
      strm - destination stream
      hdr - the header to write
      Throws:
      IOException
    • writeEmptyPrimary

      public static void writeEmptyPrimary(DataOutput strm) throws IOException
      Writes a null header representing an empty primary HDU to a stream.
      Parameters:
      strm - stream to write to
      Throws:
      IOException
    • getDataSize

      public static long getDataSize(nom.tam.fits.Header hdr)
      Utility function to find the number of bytes in the data segment of an HDU. As far as I can see, Header.getDataSize() ought to do this, but it doesn't seem to.
      Parameters:
      hdr - the Header
      Returns:
      the number of bytes in the data segment associated with hdr
    • addTrimmedValue

      public static void addTrimmedValue(nom.tam.fits.Header hdr, String key, String value, String comment) throws nom.tam.fits.HeaderCardException
      Adds a string-valued card to the header. If the value is too long, it is truncated appropriately, and a warning is emitted through the logging system.
      Parameters:
      hdr - header
      key - card key
      value - card value
      comment - card comment
      Throws:
      nom.tam.fits.HeaderCardException
    • addStringValue

      public static void addStringValue(nom.tam.fits.Header hdr, String key, String value, String comment)
      Attempts to add a string-valued card to the header. If the value is too long, no header is added, and a message is emitted through the logging system.
      Parameters:
      hdr - header
      key - card key
      value - card value
      comment - card comment