ISO/IEC 7942-2:1997

INTERNATIONAL ISO/IEC
7942-2
STANDARD
First edition
1997-09-01
Information technology - Computer
graphics and image processing -
Graphical Kernel System (GKS) -
Part 2:
NDC metafile
Technologies de /‘information -
lnfographie et traitement d’image -
Systeme graphique Kernel (GKS) -
Parfie 2: M6tafichier NDC
Reference number
ISOAEC 7942-2: 1997(E)

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ISO/IEC 7942-2: 1997(E)
Contents
V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Foreword . . . . . . . . . . . . . . . . . . . .
vi
......................................................................................................
Introduction
1
......................................................................................................................
1 Scope
2
.............................................................................................
2 Normative references
3
............................................................................................................
3 Definitions.
4
.................................................................................................................
4 Concepts
................................................... 4
4.1 The structure of a GKS-94 NDC metafile
4
........................................................................................
4.2 Metafile elements
4
.......................................................................................
4.3 Delimiter elements
4
........................................................................
4.4 Metafile descriptor elements
4
...............................................................................
4.4.1 Elements used
.................................................................... 5
4.4.2 Functional capability
5
4.4.3 NDC-SET .
6
.........................................................................................
4.5 Control elements
6
.......................................................................
4.6 Graphical primitive elements
7
.......................................................................................
4.7 Attribute elements
8
....................................................................
4.8 Application structure elements
9
.............................................................................................
4.9 Metafile states
11
................................................................
5 Abstract specification of new elements
..................................................... 11
5.1 Data type definitions and abbreviations
11
.....................................................................................
5.2 Delimiter elements
11
......................................................................
5.3 Metafile descriptor elements
11
.......................................................................................
5.4 Control elements
12
.....................................................................
5.5 Graphical primitive elements
12
.....................................................................................
5.6 Attribute elements
13
.......................................................................................
5.7 Metafile defaults
14
......................................................
6 Mapping from NDC picture to NDC metafile
14
6.1 Introduction .
14
......................................................................................
6.2 Output primitives
14
..................................................................
6.2.1 SET OF POLYLINE
14
...........................................................................
6.2.2 SET OF NURB
........................................................ 14
6.2.3 SET OF CONIC SECTION
15
.........................................................................
6.2.4 POLYMARKER
0 ISO/IEC 1997
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Printed in Switzerland

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ISO/IEC 7942-2: 1997(E)
0 ISO/IEC
15
..................................................................
6.2.5 SET OF FILL AREA
15
....................................................
6.2.6 SET OF ELLIPTIC SECTOR
15
.................................................
6.2.7 SET OF ELLIPTIC SEGMENT
16
...........................................................
6.2.8 SET OF ELLIPTIC DISC
16
..........................................................
6.2.9 SET OF CLOSED NURB
16
. . .
6.2.10 TEXT
16
6.2.11 CELL ARRAY .
16
6.2.12 DESIGN PRIMITIVE .
............................. 18
6.2.13 GENERALIZED DRAWING PRIMITIVE
18
... .....................................................................................
6.3 Output attributes
18
6.3.1 SCISSOR SET .
................... .19
6.3.2 TEXT UP VECTOR and TEXT SKEW ANGLE.
19
6.3.3 CHARACTER FONT AND PRECISION .
19
6.3.4 COLOUR SPECIFIER .
21
.......................................
7 The Character Encoding of the GKS-94 NDC Metafile
21
..............................................................................
7.1 Notational conventions
21
.....................................................................
7.2 Method of encoding opcodes
21
................................................................................
7.2.1 Introduction
21
...............................................................................
7.2.2 Opcode assignments
22
................................................................
7.3 Method of encoding parameters
22
................................................................
7.4 Representation of new elements
22
................................................................................
7.4.1 Introduction
22
......................................................................
7.4.2 Delimiter elements
22
.......................................................
7.4.3 Metafile descriptor elements
22
.........................................................................
7.4.4 Control elements
23
......................................................
7.4.5 Graphical primitive elements
24
.......................................................................
7.4.6 Attribute elements
24
...................................................
7.4.7 Application structure elements
27
...........................................
8 The Binary Encoding of the GKS-94 NDC Metafile
27
8.1 Overall structure . . .
27
8.2 Primitive data forms .
27
...............................................
8.3 Representation of abstract parameter types
27
.................................................................
8.4 Representation of each element
27
8.4.1 Introduction .
27
......................................................................
8.4.2 Delimiter elements
27
.......................................................
8.4.3 Metafile descriptor elements
28
8.4.4 Control elements .
...................................................... 28
8.4.5 Graphical primitive elements
29
8.4.6 Attribute elements .
30
8.4.7 Structure attribute elements .
..................................... 32
9 The Clear Text Encoding of the GKS-94 NDC Metafile
32
. . . . . . . . . . . . . . . . . . . . .*.
9.1 Notational conventions
32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.2 Encoding parameter types
32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9.3 Forming names
32
9.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
9.3.2 Words deleted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
9.3.3 Words used unabbreviated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32
9.3.4 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
9.3.5 The derived names of new elements
iii

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ISO/IEC 7942-2: 1997(E)
9.4 Encoding the NDC Metafile elements . 33
9.4.1 Introduction . 33
9.4.2 Encoding delimiter elements . 33
....................................... 33
9.4.3 Encoding metafile descriptor elements
......................................................... 33
9.4.4 Encoding control elements
...................................... 33
9.4.5 Encoding graphical primitive elements
34
9.4.6 Encoding attribute elements .
............................... 34
9.4.7 Encoding of application structure elements
37
................................................................................................
A Formal grammar.
37
..............................................................................................
A.1 Introduction
37
..................................................................................................
A.2 Notation.
37
.....................................................................................
A.3 Detailed grammar
37
A.3.1 Metafile structure .
...................................................... 37
A.3.2 Metafile descriptor elements
........................................................ 38
A.3.3 Picture descriptor elements
38
A.3.4 Control elements .
39
A.3.5 Graphical elements .
44
......................................................................
A.3.6 Attribute elements
49
......................................................................
A.3.7 Terminal symbols
54
..................................................................................................
B New element list
54
..............................................................................................
B.l Introduction
54
....................................................................................
B.2 Delimiter elements
54
.....................................................................
B.3 Metafile descriptor elements
54
......................................................................................
B.4 Control elements
54
....................................................................
B.5 Graphical primitive elements
54
.....................................................................................
B.6 Attribute elements
iv

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@ ISO/IEC
ISO/IEC 7942-2: 1997(E)
Foreword
IS0 (the International Organization for Standardization) and IEC (the International Electrotechnical Commis-
sion) form the specialized system for worldwide standardization.
National bodies that are members of IS0 or
IEC participate in the development of International Standards through technical committees established by the
respective organization to deal with particular fields of technical activity. IS0 and IEC technical committees
collaborate in fields of mutual interest. Other international organizations, governmental and non-
governmental, in liaison with IS0 and IEC, also take part in the work.
In the field of information technology, IS0 and IEC have established a joint technical committee, ISO/IEC
JTCl. Draft International Standards adopted by the joint technical committee are circulated to national bodies
for voting. Publication as an International Standard requires approval by at least 75 % of the national bodies
casting a vote.
International Standard ISO/IEC 7942-2 was prepared by Joint Technical Committee ISO/IEC JTCl, Informa-
tion technology, Subcommittee SC24, Computer graphics and image processing.
ISO/IEC 7942 consists of the following parts, under the general title Information technology - Computer
graphics and image processing - Graphical Kernel System (GKS) :
Part I: Functional description
Part 2: NDC metaBle
Part 3: Audit trail
Part 4: Picture part archive
Annexes A and B form an integral part of this part of ISOLIEC 7942.

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0 ISO/IEC
ISO/IEC 7942-2: 1997(E)
Introduction
The NDC metafile provides a file format and encodings suitable for the storage and retrieval of picture infor-
mation. The file format consists of a set of elements that can be used to describe pictures in a way that is com-
patible between systems of different architectures and devices of differing capabilities and design, This part of
ISO/IEC 7942 extends the provisions of ISO/IEC 8632: 1992/Amd.2: 1995.
vi

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ISO/IEC 7942-2: 1997(E)
INTERNATIONAL STANDARD OISOKEC
Information technology - Computer graphics and image processing -
Graphical Kernel System (GKS) - Part 2: NDC metafile
1 Scope
This part of ISO/IEC 7942 provides a file format and encodings for the storage and retrieval of GKS-94 Nor-
malized Device Coordinate (NDC) pictures. It is an extension of the Computer Graphics Metafile, Version 4
defined by ISO/IEC 8632: 1992/Amd.2: 1995 (all parts).

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ISO/IEC 7942=2:1997(E) OISOIIEC
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this
part of ISO/IEC 7942. At the time of publication, the editions indicated were valid. All standards are subject to
revision, and parties to agreements based on this part of ISO/IEC 7942 are encouraged to investigate the possi-
bility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain
registers of currently valid International Standards.
Computer graphics and image processing - Graphical Kernel
ISO/IEC 7942- 1: 1994, Information technology -
System (GKS) - Part 1: Functional description.
ISOAEC 8632: 1992lAmd.2: 1995, Information technology - Computer graphics - Metafile for transfer and
storage of picture description information (all parts).
2

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ISOiIEC ‘7942-2: 1997(E)
0 ISO/IEC
3 Definitions
For the purposes of this part of ISO/IEC 7942, the definitions given in ISO/IEC 7942-l and ISO/IEC 8632-
UAmd.2 apply.

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OISO/IEC
ISO/IEC 7942-2: 1997(E)
4 Concepts
4.1 The structure of a GKS-94 NDC metafile
The structure of a GKS-94 NIX Metafile follows the Computer Graphics Metafile (CGM) standard (ISO/IEC
8632-l : 1992). It is shown in figure 1. MF is used as an abbreviation for METAFILE.
1 BEGIN NDC MF ( MD 1 . 1 END MF ]
Figure 1: General form of metafile
A Computer Graphics Metafile is a collection of elements from the standardized set. The BEGIN NDC
METAFILE element is followed by the METAFILE DESCRIPTOR (MD). After this the pictures follow, each
logically independent of each other. Finally the Metafile is ended with an END METAFILE element.
Apart from the BEGIN NDC METAFILE, END METAFILE and Metafile Descriptor elements, the metafile is
partitioned into pictures. All pictures are mutually independent. A picture consists of a BEGIN PICTURE ele-
ment, a PICTURE DESCRIPTOR (PD) element, a BEGIN PICTURE BODY element, an arbitrary number of
control, graphical and attribute elements and finally an END PICTURE element (see figure 2). PIC is used as
an abbreviation for PICTURE and BEGIN BODY for BEGIN PICTURE BODY.
BEGIN PIC PD BEGIN BODY . . . END PIC
I
Figure 2: General form of pictures
4.2 Metafile elements
Elements in CGM Version 4 are used for the mapping of NDC picture to NDC metafile wherever possible.
However, some new elements are introduced to provide functionality required by the NDC metafile which can-
not be described within CGM Version 4. The new CGM elements are marked by daggers (f) in the tables in
this section. The scope of some CGM Version 4 elements has been extended. These elements are marked
with a double dagger ($).
4.3 Delimiter elements
The NDC metafile includes the following delimiter elements:
BEGIN NDC METAFILE? BEGIN PICTURE BODY
END METAFILE BEGIN APPLICATION STRUCTURE
BEGIN PICTURE BEGIN APPLICATION STRUCTURE BODY
END PICTURE END APPLICATION STRUCTURE
In NDC metafiles, primitives of the same type may be grouped together to form a set of primitives. The primi-
tives to be included in the set of primitives being defined are delimited by application structure elements as
described in 6.2. Application structure elements are also used in the representation of the design primitive (see
6.2.12) and the SCISSOR SET primitive attribute (see 6.3.1).
4.4 Metafile descriptor elements
4.4.1 Elements used
The NDC metafile includes the following metafile descriptor elements:

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0 ISO/IEC ISO/IEC 7942-2: 1997(E)
Concepts Metafile descriptor elements
METAFILE VERSION METAFILE ELEMENT LIST
VDC TYPE MAXIMUM VDC EXTENT
MAXIMUM COLOUR INDEX
The METAFILE ELEMENT LIST lists at least those standardized elements that occur in the metafile.
4.4.2 Functional capability
Following the provisions of ISO/IEC 8632-l : 19921Amd.2: 1995, the contents of the Computer Graphics
These shall contain a list of the non-
Metafile are defined by the METAFILE ELEMENT LIST element.
mandatory elements that are utilized in the metafile. Several shorthand names for CGM elements are also pro-
vided for use with the METAFILE ELEMENT LIST. The NDC metafile set is designated NDC-SET. These
shorthand names shall not be considered macro names, nor shall they be construed to be levels of confor-
mance.
4.4.3 NDC-SET
The NDC-SET includes the elements which can appear in the NDC Metafile. The elements which are not
marked by daggers belong to the CGM Version-4 set. The value ranges of some of the parameters of some
CGM elements have been extended. These elements are marked by double daggers. The elements included in
the NDC-metafile are:
’ ’
’
f










’
























f




’







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OISO/IEC
ISO/IEC 7942=2:1997(E)
Concepts
Metafile descriptor elements
’


?
f
4.5 Control elements
In GKS-94 CLIP INDICATOR and CLIP RECTANGLE elements are the parts of the definition of an output
primitive attribute, scissor set. The new control elements SCISSOR IDENTIFIER and SHIELD INDICATOR
are used to provide the mapping of the GKS-94 SCISSOR SET attribute (see 4.7).
CGM element
GKS elements
CLIP INDICATOR
CLIP INDICATOR
CLIP RECTANGLE
CLIP RECTANGLE
SCISSOR IDENTIFIERf
SHIELD INDICATOR?
4.6 Graphical primitive elements
Graphical primitive elements are those elements that describe the visual components of a picture. Their coordi-
nate arguments, if any, are specified in VDC units.
The mapping of GKS-94 output primitives to CGM elements is shown in the table below. An extension to
CGM was needed to provide this mapping. The new CGM elements are marked by asterisks.
Each GKS-94 output primitive marked by an asterisk (*) is mapped to a set of the corresponding CGM ele-
ments delimited by BEGIN APPLICATION STRUCTURE and END APPLICATION STRUCTURE ele-
ments. The DESIGN primitive is more complicated and its mapping to the CGM elements is described in
clause 6.
The CELL ARRAY primitive is mapped to a set of elements which define the way in which the colour values
used in the following CELL ARRAY element are defined.
GKS elements CGM element
SET OF POLYLINE- POLYLINE
SET OF NURB* NON-UNIFORM RATIONAL B-SPLINE
SET OF CONIC SECTION* CONIC SECTION?
POLYMARKER POLYMARKER
SET OF FILL AREA* POLYGON
SET OF ELLIPTIC SECTOR* CONIC SECTION’
SET OF ELLIPTIC SEGMENT* CONIC SECTIONf
SET OF ELLIPTIC DISC* ELLIPTIC DISC’
NON-UNIFORM RATIONAL B-SPLINE
SET OF CLOSED NURB*
TEXT
TEXT
COLOUR VALUE EXTENT
CELL ARRAY
COLOUR PRECISION
COLOUR MODEL
COLOUR SELECTION MODE
CELL ARRAY
Several elements ’
DESIGN
GENERALIZED DRAWING PRIMITIVE
GENERALIZED DRAWING PRIMITIVE
The CONIC SECTION element specifies a conic section defined by a 3 x 3 matrix (which specifies the conic)
and two points which define the start and end points of the conic section. The last parameter of the conic
6

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ISO/IEC 7942-2: 1997(E)
0 ISO/IEC
Concepts Graphical primitive elements
section definition is a sense flag which indicates whether it is the clockwise or anti-clockwise section that is
required when the conic is closed.
The ELLIPTIC DISC element is defined by a 3 x 3 matrix which defines the ellipse.
4.7 Attribute elements
The mapping of GKS-94 output primitive attributes to CGM elements is shown in the table below. An exten-
sion to ISOIIEC 8632-l : 1992/Amd.2: 1995 was needed to provide this mapping. The new or revised CGM ele-
ments are marked by asterisks. The GKS-94 SCISSOR SET attribute is stored in the NDC Metafile using
several elements as explained in 6.3. I.
CGM elements
GKS attribute
PICK IDENTIFIER
PICK IDENTIFIER
NAMESET?
NAMESET
SCISSOR IDENTIFIER?
SCISSOR SET
CLIP INDICATOR
CLIP RECTANGLE
SHIELD INDICATOR?
GLOBAL TRANSFORMATION’
GLOBAL TRANSFORMATION
LOCAL TRANSFORMATION LOCAL TRANSFORMATION?
PATTERN SIZE
PATTERN SIZE
FILL REFERENCE POINT
PATTERN REFERENCE POINT
CHARACTER HEIGHT
TEXT HEIGHT
CHARACTER ORIENTATION
TEXT UP VECTOR
~ CHARACTER ORIENTATION
TEXT SKEW ANGLE
~ TEXT PATH
TEXT PATH
~ TEXT ALIGNMENT
TEXT ALIGNMENT
CURVE INDEX ~ LINE BUNDLE INDEX
CURVE ASFS ASPECT SOURCE FLAGS’
CURVE TYPE ~ LINE TYPE
CURVEWIDTH SCALE FACTOR LINE WIDTH
CURVE COLOUR SPECIFIER COLOUR SELECTION MODE
COLOUR VALUE EXTENT
COLOUR PRECISION
COLOUR MODEL
LINE COLOUR
MARKER INDEX MARKER BUNDLE INDEX
MARKER ASFS ASPECT SOURCE FLAGS’
MARKER TYPE MARKER TYPE
MARKER SIZE SCALE FACTOR MARKER SIZE
COLOUR SELECTION MODE
MARKER COLOUR SPECIFIER
COLOUR VALUE EXTENT
COLOUR PRECISION
COLOUR MODEL
MARKER COLOUR
FILL BUNDLE INDEX
AREA INDEX
ASPECT SOURCE FLAGS’
AREA ASFS
INTERIOR STYLE
INTERIOR STYLE
HATCH INDEX
INTERIOR STYLE INDEX

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OISO/IEC
ISO/IEC 7942-2: 1997(E)
Concepts
Attribute elements
CGM elements
GKS attribute
INTERIOR COLOUR SPECIFIER COLOUR SELECTION MODE
COLOUR VALUE EXTENT
COLOUR PRECISION
COLOUR MODEL
FILL COLOUR
EDGE VISIBILITY
EDGE FLAG
EDGE TYPE
EDGE TYPE
EDGE WIDTH
EDGEWIDTH SCALE FACTOR
COLOUR SELECTION MODE
EDGE COLOUR SPECIFIER
COLOUR VALUE EXTENT
COLOUR PRECISION
COLOUR MODEL
EDGE COLOUR
TEXT BUNDLE INDEX
CHARACTER INDEX
CHARACTER ASFS ASPECT SOURCE FLAGS
CHARACTER FONT AND PRECISION TEXT FONT INDEX
TEXT PRECISION
CHARACTER EXPANSION FACTOR
CHARACTER EXPANSION FACTOR
CHARACTER SPACING CHARACTER SPACING
CHARACTER COLOUR SPECIFIER COLOUR SELECTION MODE
COLOUR VALUE EXTENT
COLOUR PRECISION
COLOUR MODEL
TEXT COLOUR
4.8 Application structure elements
The NDC metafile uses application structure elements in Version 4 CGM to represent ‘set of’ output primi-
The following application structure types are used.
tives, the design output primitive and scissor sets.


















Application structure attributes are used to represent the parameters of design primitives, stencil, contour and
The application structure attribute types used and the composition of their
tiling component attributes.
8

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0 ISO/IEC ISO/IEC 7942-2: 1997(E)
Concepts
Application structure elements
associated structured data records are listed in the table below.
Attribute
Parameter Type
Stencil origin P
PARAMETERS>
Stencil transformation (2x3)R
Tiling origin P
Tiling transformation
(2x3)R
Inside rule (one of: evenodd, winding)E
ENUMERATED>
ATTRIBUTES> CAPY R
HALFY R
BASEY R
BOTTOMY R
CENTREY R
LEFTX R
RIGHTX R
CENTREX R
CENTRE P
ORIGIN P
CENTRETOP
P
CENTREBOTTOM
P
CENTRELEFT
P
CENTRERIGHT
P
TOPLEFT
P
TOPRIGHT
P
BOTTOMLEFT
P
BOTTOMRIGHT
P
(one of: solid, dashed, dotted,
ATTRIBUTES> dashed-dotted, dashed-dashed-dotted)IX
WIDTH R
CAP (one of: butted, rounded, square)IX
JOIN (one of: round, bevel, mitred)IX
mi tred R
ATTRIBUTES> Replication technique (one of: dx, dy, dxdy, dydx)E
Replication technique x value R
Replication technique y value R
4.9 Metafile states
The table below shows the major metafile states in which the new metafile elements introduced in this Interna-
tional Standard are allowed. This table extends Table 8 in ISOIIEC 8632-l: 1992lAmd.2: 1995. The new ele-
ments are not allowed in any of the CGM minor states.

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ISO/IEC 7942-2: 1997(E)
OISO/IEC
Metafile states
Concepts
NDC Metafile Major States
Element PCS MDS DR GSS, PDS
POS LSS SDS SOS
DSS
BEGIN NDC METAFILE
SCISSOR IDENTIFIER
X
SHIELD INDICATOR
X
CONIC SECTION X
X X X
ELLIPTIC DISC X
X X X
NAMESET X X X
X
GLOBAL TRANSFORMATION X X X
X
LOCAL TRANSFORMATION X X X X
10

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ISO/IEC 7942-2: 1997(E)
0 ISO/IEC
5 Abstract specification of new elements
5.1 Data type definitions and abbreviations
Data type definitions are the same as those used in CGM Version 4.
5.2 Delimiter elements
BEGIN NDC METAFILE
identifier S
This is the first element of an NDC metafile. It demarcates the beginning of the Metafile Descriptor. BEGIN
NDC METAFILE shall occur exactly once in a metafile. The identifier parameter is available for use by
metafile generators and interpreters in a manner that is not further standardized.
5.3 Metafile descriptor elements
COLOUR MODEL
colour model
...