FITS standard

StructureRepresentationInformation · http://example.org/archive/structure-representation-information-36053ec2

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comment Every HDU of any FITS file (FITS Standard 4.0, IAU FITS Working Group 2018): the header keyword records to END, filled to a 2880-byte block, and the data, sized by the mandatory keywords BITPIX, NAXISn, PCOUNT and GCOUNT (Eqs. 1 and 2): arrays read as BITPIX's type, binary-table rows as bytes, ASCII-table rows as text. Random groups and the columns of binary tables are not read.
label FITS standard: DFDL description of any FITS file (FITS Standard 4.0)
specificationLanguage DFDL
specificationText <?xml version="1.0" encoding="UTF-8"?> <!-- Any FITS file, as the FITS Standard 4.0 (IAU FITS Working Group, 2018) defines it: a primary HDU, then any extensions, each HDU a header of 80-character keyword records ending with END, filled with blank records to a 2880-byte block, then its data, filled with zeros to a 2880-byte block. Sizes come from the mandatory keywords, which the Standard puts at fixed positions (Tables 7, 10, 13, 14, 17): SIMPLE or XTENSION, BITPIX, NAXIS, NAXIS1 ... NAXISn, and in an extension PCOUNT and GCOUNT. The data has |BITPIX| x (NAXIS1 x ... x NAXISm) bits in a primary HDU (Eq. 1) and |BITPIX| x GCOUNT x (PCOUNT + NAXIS1 x ... x NAXISm) bits in an extension (Eq. 2). DFDL expressions have no product over a repeated element, so the product is written out for up to 9 axes; more are refused. The primary array and IMAGE extensions are read as values of BITPIX's type (8: unsigned bytes; 16, 32, 64: two's complement integers; -32, -64: IEEE 754 floats), big-endian, the first axis varying fastest; a BINTABLE's rows as bytes, then its heap (PCOUNT bytes); a TABLE's rows as text; any other extension as bytes. A binary table's columns are defined by its TFORMn keywords, which can be anywhere in the header, and DFDL can't look a keyword up by name, so its rows aren't split into fields. For the same reason random groups (whose GROUPS, PCOUNT and GCOUNT can be anywhere in the primary header) aren't read: a primary HDU with NAXIS1 = 0 is refused. Keyword values other than the mandatory integers are left as the text of their records. --> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:dfdl="http://www.ogf.org/dfdl/dfdl-1.0/" xmlns:fn="http://www.w3.org/2005/xpath-functions" xmlns:tns="urn:fits:standard:4.0" targetNamespace="urn:fits:standard:4.0" elementFormDefault="qualified"> <xs:include schemaLocation="/org/apache/daffodil/xsd/DFDLGeneralFormat.dfdl.xsd"/> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:format ref="tns:GeneralFormat" representation="binary" byteOrder="bigEndian" binaryNumberRep="binary" lengthKind="explicit" lengthUnits="bytes" encoding="US-ASCII" occursCountKind="implicit" textTrimKind="padChar" textPadKind="padChar" textStringJustification="left" textStringPadCharacter="%SP;"/> </xs:appinfo> </xs:annotation> <!-- A keyword record whose value is a fixed-format integer, right-justified in bytes 11 to 30 (Sect. 4.2.3). --> <xs:complexType name="integerRecord"> <xs:sequence> <xs:element name="keyword" type="xs:string" dfdl:representation="text" dfdl:length="8"/> <xs:element name="indicator" type="xs:string" dfdl:representation="text" dfdl:length="2" dfdl:textTrimKind="none" dfdl:textPadKind="none"/> <xs:element name="value" type="xs:long" dfdl:representation="text" dfdl:length="20" dfdl:textNumberRep="standard" dfdl:textNumberPattern="#0" dfdl:textNumberCheckPolicy="lax" dfdl:textNumberJustification="right" dfdl:textNumberPadCharacter="%SP;"/> <xs:element name="comment" type="xs:string" dfdl:representation="text" dfdl:length="50"/> </xs:sequence> </xs:complexType> <!-- Any other keyword record: its keyword, and bytes 9 to 80 as text. --> <xs:complexType name="record"> <xs:sequence> <xs:element name="keyword" type="xs:string" dfdl:representation="text" dfdl:length="8"/> <xs:element name="text" type="xs:string" dfdl:representation="text" dfdl:length="72"/> </xs:sequence> </xs:complexType> <xs:element name="fits" dfdl:lengthKind="implicit"> <xs:complexType> <xs:sequence> <xs:element name="hdu" maxOccurs="unbounded" dfdl:lengthKind="implicit"> <xs:complexType> <xs:sequence> <xs:element name="header" dfdl:lengthKind="implicit"> <xs:complexType> <xs:sequence> <xs:element name="first" type="tns:record" dfdl:lengthKind="implicit"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:discriminator test="{ tns:keyword eq 'SIMPLE' or tns:keyword eq 'XTENSION' }" message="An HDU begins with SIMPLE (the primary HDU) or XTENSION (an extension)."/> </xs:appinfo> </xs:annotation> </xs:element> <xs:element name="bitpix" type="tns:integerRecord" dfdl:lengthKind="implicit"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:assert test="{ tns:keyword eq 'BITPIX' and (tns:value eq 8 or tns:value eq 16 or tns:value eq 32 or tns:value eq 64 or tns:value eq -32 or tns:value eq -64) }" message="The second keyword must be BITPIX, with 8, 16, 32, 64, -32 or -64."/> </xs:appinfo> </xs:annotation> </xs:element> <xs:element name="naxis" type="tns:integerRecord" dfdl:lengthKind="implicit"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:assert test="{ tns:keyword eq 'NAXIS' and tns:value ge 0 and tns:value le 9 }" message="The third keyword must be NAXIS; this description reads up to 9 axes."/> </xs:appinfo> </xs:annotation> </xs:element> <xs:element name="naxisn" type="tns:integerRecord" minOccurs="0" maxOccurs="9" dfdl:lengthKind="implicit" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../tns:naxis/tns:value }"/> <xs:element name="pcount" type="tns:integerRecord" minOccurs="0" maxOccurs="1" dfdl:lengthKind="implicit" dfdl:occursCountKind="expression" dfdl:occursCount="{ if (../tns:first/tns:keyword eq 'XTENSION') then 1 else 0 }"/> <xs:element name="gcount" type="tns:integerRecord" minOccurs="0" maxOccurs="1" dfdl:lengthKind="implicit" dfdl:occursCountKind="expression" dfdl:occursCount="{ if (../tns:first/tns:keyword eq 'XTENSION') then 1 else 0 }"/> <xs:element name="card" type="tns:record" minOccurs="0" maxOccurs="unbounded" dfdl:lengthKind="implicit"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:discriminator test="{ tns:keyword ne 'END' }"/> </xs:appinfo> </xs:annotation> </xs:element> <xs:element name="end" type="tns:record" dfdl:lengthKind="implicit"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:assert test="{ tns:keyword eq 'END' }" message="A header ends with END."/> </xs:appinfo> </xs:annotation> </xs:element> <!-- Blank records filling the header's last 2880-byte block (36 records). --> <xs:element name="fill" type="xs:string" dfdl:representation="text" dfdl:length="{ ((36 - (fn:count(../tns:card) + 4 + xs:integer(../tns:naxis/tns:value) + (if (../tns:first/tns:keyword eq 'XTENSION') then 2 else 0)) mod 36) mod 36) * 80 }"/> <!-- What the data is, and how big, from the mandatory keywords (Eqs. 1 and 2). --> <xs:element name="kind" type="xs:string" dfdl:inputValueCalc="{ if (../tns:first/tns:keyword eq 'SIMPLE') then 'PRIMARY' else if (fn:contains(../tns:first/tns:text, &quot;'IMAGE&quot;)) then 'IMAGE' else if (fn:contains(../tns:first/tns:text, &quot;'BINTABLE&quot;)) then 'BINTABLE' else if (fn:contains(../tns:first/tns:text, &quot;'TABLE&quot;)) then 'TABLE' else 'OTHER' }"> <xs:annotation> <xs:appinfo source="http://www.ogf.org/dfdl/"> <dfdl:assert test="{ . ne 'PRIMARY' or xs:integer(../tns:naxis/tns:value) eq 0 or xs:integer(../tns:naxisn[1]/tns:value) ne 0 }" message="A primary HDU with NAXIS1 = 0 holds random groups, which this description doesn't read."/> </xs:appinfo> </xs:annotation> </xs:element> <xs:element name="elements" type="xs:long" dfdl:inputValueCalc="{ if (xs:integer(../tns:naxis/tns:value) eq 0) then 0 else xs:integer(../tns:naxisn[1]/tns:value) * (if (xs:integer(../tns:naxis/tns:value) ge 2) then xs:integer(../tns:naxisn[2]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 3) then xs:integer(../tns:naxisn[3]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 4) then xs:integer(../tns:naxisn[4]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 5) then xs:integer(../tns:naxisn[5]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 6) then xs:integer(../tns:naxisn[6]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 7) then xs:integer(../tns:naxisn[7]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 8) then xs:integer(../tns:naxisn[8]/tns:value) else 1) * (if (xs:integer(../tns:naxis/tns:value) ge 9) then xs:integer(../tns:naxisn[9]/tns:value) else 1) }"/> <xs:element name="data_bytes" type="xs:long" dfdl:inputValueCalc="{ (fn:abs(xs:integer(../tns:bitpix/tns:value)) idiv 8) * (if (../tns:first/tns:keyword eq 'XTENSION') then xs:integer(../tns:gcount[1]/tns:value) * (xs:integer(../tns:pcount[1]/tns:value) + xs:integer(../tns:elements)) else xs:integer(../tns:elements)) }"/> <xs:element name="layout" type="xs:string" dfdl:inputValueCalc="{ if (../tns:kind eq 'PRIMARY' or ../tns:kind eq 'IMAGE') then fn:concat('array', xs:string(../tns:bitpix/tns:value)) else ../tns:kind }"/> </xs:sequence> </xs:complexType> </xs:element> <xs:element name="data" dfdl:lengthKind="explicit" dfdl:length="{ ../tns:header/tns:data_bytes }"> <xs:complexType> <xs:choice dfdl:choiceDispatchKey="{ ../tns:header/tns:layout }"> <xs:element name="unsigned_bytes" dfdl:choiceBranchKey="array8" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="value" type="xs:unsignedByte" dfdl:length="1" minOccurs="0" maxOccurs="unbounded" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:elements }"/> </xs:sequence></xs:complexType> </xs:element> <xs:element name="int16" dfdl:choiceBranchKey="array16" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="value" type="xs:short" dfdl:length="2" minOccurs="0" maxOccurs="unbounded" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:elements }"/> </xs:sequence></xs:complexType> </xs:element> <xs:element name="int32" dfdl:choiceBranchKey="array32" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="value" type="xs:int" dfdl:length="4" minOccurs="0" maxOccurs="unbounded" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:elements }"/> </xs:sequence></xs:complexType> </xs:element> <xs:element name="int64" dfdl:choiceBranchKey="array64" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="value" type="xs:long" dfdl:length="8" minOccurs="0" maxOccurs="unbounded" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:elements }"/> </xs:sequence></xs:complexType> </xs:element> <xs:element name="float32" dfdl:choiceBranchKey="array-32" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="value" type="xs:float" dfdl:length="4" dfdl:binaryFloatRep="ieee" minOccurs="0" maxOccurs="unbounded" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:elements }"/> </xs:sequence></xs:complexType> </xs:element> <xs:element name="float64" dfdl:choiceBranchKey="array-64" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="value" type="xs:double" dfdl:length="8" dfdl:binaryFloatRep="ieee" minOccurs="0" maxOccurs="unbounded" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:elements }"/> </xs:sequence></xs:complexType> </xs:element> <!-- A binary table: NAXIS2 rows of NAXIS1 bytes, then the heap (PCOUNT bytes). --> <xs:element name="binary_table" dfdl:choiceBranchKey="BINTABLE" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="row" type="xs:hexBinary" minOccurs="0" maxOccurs="unbounded" dfdl:length="{ ../../../tns:header/tns:naxisn[1]/tns:value }" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:naxisn[2]/tns:value }"/> <xs:element name="heap" type="xs:hexBinary" dfdl:length="{ ../../../tns:header/tns:pcount[1]/tns:value }"/> </xs:sequence></xs:complexType> </xs:element> <!-- An ASCII table: NAXIS2 rows of NAXIS1 characters. --> <xs:element name="ascii_table" dfdl:choiceBranchKey="TABLE" dfdl:lengthKind="implicit"> <xs:complexType><xs:sequence> <xs:element name="row" type="xs:string" dfdl:representation="text" minOccurs="0" maxOccurs="unbounded" dfdl:length="{ ../../../tns:header/tns:naxisn[1]/tns:value }" dfdl:occursCountKind="expression" dfdl:occursCount="{ ../../../tns:header/tns:naxisn[2]/tns:value }"/> </xs:sequence></xs:complexType> </xs:element> <!-- Any other extension: its data as bytes. --> <xs:element name="bytes" type="xs:hexBinary" dfdl:choiceBranchKey="OTHER" dfdl:length="{ ../../tns:header/tns:data_bytes }"/> </xs:choice> </xs:complexType> </xs:element> <!-- Zeros filling the data's last 2880-byte block. --> <xs:element name="fill" type="xs:hexBinary" dfdl:length="{ (2880 - (xs:integer(../tns:header/tns:data_bytes) mod 2880)) mod 2880 }"/> </xs:sequence> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> </xs:element> </xs:schema>

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