Package uk.ac.starlink.fits
Class FitsConstants
- java.lang.Object
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- uk.ac.starlink.fits.FitsConstants
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public class FitsConstants extends java.lang.Object
Utility class providing some constants and static methods related to FITS file format and starlink classes.- Author:
- Mark Taylor (Starlink)
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Field Summary
Fields Modifier and Type Field Description static nom.tam.fits.HeaderCard
END_CARD
Image of end-of-header card.static int
FITS_BLOCK
Standard size of a FITS block in bytes.static int
MAX_NCOLSTD
Maximum number of columns in standard FITS BINTABLE extension.static java.lang.String
NDARRAY_ORIGIN
FITS header card for indicating NDArray origin values.static java.lang.String
NDARRAY_PREFIX
Prefix for NDArray-related FITS header cards.static java.lang.String
NDX_PREFIX
Prefix for NDX-related FITS header cards.static java.lang.String
NDX_XML
FITS header card for location (relative URL) of XML representation.static boolean
REQUIRE_HIERARCH
Whether HIERARCH convention is used; true by default.static java.lang.String
WCS_ENCODING
Default encoding used for writing WCS into FITS headers.
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Constructor Summary
Constructors Constructor Description FitsConstants()
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Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description static void
addStringValue(nom.tam.fits.Header hdr, java.lang.String key, java.lang.String value, java.lang.String comment)
Attempts to add a string-valued card to the header.static void
addTrimmedValue(nom.tam.fits.Header hdr, java.lang.String key, java.lang.String value, java.lang.String comment)
Adds a string-valued card to the header.static void
checkColumnCount(WideFits wide, int ncol)
Checks that a table with the given number of columns can be written.static void
configureHierarch()
Ensures that use of the HIERARCH convention when dealing with FITS headers is set to the state expected for STIL operation.static nom.tam.fits.HeaderCard
createHeaderCard(java.lang.String cardImage)
Create a HeaderCard from a FITS card image.static nom.tam.fits.Header
createUnsortedHeader()
Creates a Header instance which does not perform any unsolicited reordering of the header cards.static java.util.List<java.lang.String>
defaultFitsExtensions()
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 java.lang.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
writeEmptyPrimary(java.io.DataOutput strm)
Writes a null header representing an empty primary HDU to a stream.static void
writeHeader(java.io.DataOutput strm, nom.tam.fits.Header hdr)
Writes a header object to a DataOutput.
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Field Detail
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NDARRAY_PREFIX
public static final java.lang.String NDARRAY_PREFIX
Prefix for NDArray-related FITS header cards.- See Also:
- Constant Field Values
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END_CARD
public static final nom.tam.fits.HeaderCard END_CARD
Image of end-of-header card.
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NDARRAY_ORIGIN
public static final java.lang.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:
- Constant Field Values
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NDX_PREFIX
public static final java.lang.String NDX_PREFIX
Prefix for NDX-related FITS header cards.- See Also:
- Constant Field Values
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NDX_XML
public static final java.lang.String NDX_XML
FITS header card for location (relative URL) of XML representation.- See Also:
- Constant Field Values
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WCS_ENCODING
public static final java.lang.String WCS_ENCODING
Default encoding used for writing WCS into FITS headers.- See Also:
- Constant Field Values
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FITS_BLOCK
public static final int FITS_BLOCK
Standard size of a FITS block in bytes.- See Also:
- Constant Field Values
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MAX_NCOLSTD
public static final int MAX_NCOLSTD
Maximum number of columns in standard FITS BINTABLE extension.- See Also:
- Constant Field Values
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REQUIRE_HIERARCH
public static boolean REQUIRE_HIERARCH
Whether HIERARCH convention is used; true by default.
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Method Detail
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defaultFitsExtensions
public static java.util.List<java.lang.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
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configureHierarch
public static void configureHierarch()
Ensures that use of the HIERARCH convention when dealing with FITS headers is set to the state expected for STIL operation. If this involves changing the current setting, a warning is issued through the logging system.The general idea is that this is only issued once per JVM. If other components are resetting the hierarch handling that might not be enough, but there's no mechanism to ensure that it stays set anyway.
The main reason this is necessary is that WideFits handling requires HIERARCH, but there is no per-call configuration of whether the convention is in use, so it has to be set on a global basis.
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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:
- nom.tam.fits github discussion
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createHeaderCard
public static nom.tam.fits.HeaderCard createHeaderCard(java.lang.String cardImage)
Create a HeaderCard from a FITS card image.- Parameters:
cardImage
- the 80 character card image- Returns:
- card object
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headerIterable
public static java.lang.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
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skipHDUs
public static long skipHDUs(nom.tam.util.ArrayDataInput stream, int nskip) throws java.io.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 throughnskip
- the number of HDUs to skip- Returns:
- the number of bytes the stream was advanced
- Throws:
java.io.IOException
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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
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getInputStreamStart
public static nom.tam.util.ArrayDataInput getInputStreamStart(uk.ac.starlink.util.DataSource datsrc) throws java.io.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:
java.io.IOException
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readHeader
public static int readHeader(nom.tam.fits.Header hdr, nom.tam.util.ArrayDataInput strm) throws nom.tam.fits.TruncatedFileException, java.io.IOException
Populates a header from an input stream, reporting its length in bytes. This does the same asHeader.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; thoughHeader.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 populatestrm
- 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
java.io.IOException
- See Also:
Header.read(nom.tam.util.ArrayDataInput)
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writeHeader
public static void writeHeader(java.io.DataOutput strm, nom.tam.fits.Header hdr) throws java.io.IOException
Writes a header object to a DataOutput.- Parameters:
strm
- destination streamhdr
- the header to write- Throws:
java.io.IOException
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writeEmptyPrimary
public static void writeEmptyPrimary(java.io.DataOutput strm) throws java.io.IOException
Writes a null header representing an empty primary HDU to a stream.- Parameters:
strm
- stream to write to- Throws:
java.io.IOException
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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
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addTrimmedValue
public static void addTrimmedValue(nom.tam.fits.Header hdr, java.lang.String key, java.lang.String value, java.lang.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
- headerkey
- card keyvalue
- card valuecomment
- card comment- Throws:
nom.tam.fits.HeaderCardException
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addStringValue
public static void addStringValue(nom.tam.fits.Header hdr, java.lang.String key, java.lang.String value, java.lang.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
- headerkey
- card keyvalue
- card valuecomment
- card comment
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checkColumnCount
public static void checkColumnCount(WideFits wide, int ncol) throws java.io.IOException
Checks that a table with the given number of columns can be written. If the column count is not exceeded, nothing happens, but if there are too many columns an informative IOException is thrown.- Parameters:
wide
- extended column convention - may be null for FITS standard behaviour onlyncol
- number of columns to write- Throws:
java.io.IOException
- if there are too many columns
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