CGM

In This Topic

Full Name	Computer Graphics Metafile
Format ID	IG_FORMAT_CGM = 75
File Extension(s)	*.cgm
Data Type	Metafile Vector Image
Data Encoding	Character-based, Binary, Clear-text encoded
Color Profile Support	No
Multi-Page Support	Yes
Alpha Channel Support	No
ImageGear 3D Image Support	No
ImageGear Raster to Vector Format Conversion Support	No
ImageGear Unicode Text Display Support	No

To support the CGM format, attach the ImageGear CAD/Vector CGM Component to Core ImageGear. See Attaching Components.

ImageGear Supported Versions:

Version 1 (1987 standard)
Version 2
Version 3 (1992 standard)

ImageGear Supported Features:

IG_FLTR_DETECTSUPPORT - autodetection
IG_FLTR_PAGEREADSUPPORT - single page file reading
IG_FLTR_PAGEINSERTSUPPORT - single-page file writing
IG_FLTR_MPAGEREADSUPPORT - multi-page file reading

ImageGear Read Support:

IG_COMPRESSION_NONE - Vector/CAD data (binary encoded files only)

ImageGear Write Support:

IG_COMPRESSION_NONE - Vector/CAD data (binary encoded files only)

ImageGear Filter Control Parameters:

Filter Control Parameter	Type	Default Value	Available Values	Description
WIDTH	AT_INT32	512	Any positive value	Defines the width of the empty DIB associated with the image after loading. DIB height is calculated using the file's scale factors. See Working with Vector Images.

Comments:

This is a standardized platform-independent format used for the interchange of bitmap and vector data.

CGM is a very feature-rich format which attempts to support the graphic needs of many general fields (graphic arts, technical illustration, cartography, visualization, electronic publishing, and so on). While the CGM format is rich in features (many graphical primitives and attributes), it is less complex than PostScript, produces much smaller (more compact) files, and allows the interchange of very sophisticated and artistic images.

Computer Graphics Metafile was developed by experts working on committees under the auspices of the International Standards Organization (ISO) and the American Standards National Institute (ANSI). It was specifically designed as a common format for the platform-independent interchange of bitmap and vector data, and for use in conjunction with a variety of input and output devices. Although CGM incorporates extensions designed to support bitmap (called raster in the CGM specification) data storage, files in CGM format are used primarily to store vector information. CGM files typically contain either bitmap or vector data, but rarely both.

CGM Features Supported for Reading

CGM Element	Supported Attributes	Imported into ImageGear as:
Font names	Font name	HIG_VECT_FONT objects.
Color Model	Color model	Processed internally. Affects the interpretation of the colors when reading file content.
Color selection mode	Mode: True color or indexed	Processed internally. Affects the interpretation of colors.
Background color	RGB color value	Background color of the view.
VDC extent	Left Top Right Bottom	Processed internally. Affects the interpretation of different ranges. Also, used as a range of the view.
Begin Picture Body		Processed internally.
End Picture body		Processed internally.
Line and Edge type definition	Type Pattern Pattern Length	HIG_VECT_LINETYPE object.
Edge width specification mode	Mode: absolute, scaled, fraction, mm.	Processed internally. Affects the interpretation of edge width of HIG_VECT_LINETYPE object.
Line width specification mode	Mode: absolute, scaled, fraction, mm.	Processed internally. Affects the interpretation of line width of HIG_VECT_LINETYPE object.
Marker size specification mode	Mode: absolute, scaled, fraction, mm.	Processed internally. Affects the interpretation of size of Poly Marker objects.
Line representation	Line type Line width Line color	Affects the interpretation of Line and Polyline objects.
Marker representation	Marker type Marker size Marker color	Affects the interpretation of Poly Marker objects. See Poly Marker section.
Text representation	Font index Precision Spacing Expansion Color	Affects the interpretation of Text objects.
Fill representation	Font index Precision Spacing Expansion Color	Used for creating HIG_VECT_FILLTYPE object when creating the filling entity.
Edge representation	Edge type Edge width Edge color	Affects the interpretation of edges when creating such entity as IG_VECT_ENT_FIGURE (see below).
Real Precision	Fixed or floating indicator Whole part Fractional part	Processed internally. Affects the interpretation of many floating-point parameters.
Color index precision	Precision	Processed internally. Affects the interpretation of color indices.
Index precision	Precision	Processed internally. Affects the interpretation of indices for different tables.
VDC Integer precision	Precision	Processed internally. Affects the interpretation of many integer parameters.
VDC real precision	Precision	Processed internally. Affects the interpretation of many floating-point parameters.
Transparent cell colors	On/Off flag Color	Processed internally. Turns on/off the transparent color for cell array being represented by IG_VECT_RNT_RASTER (see below).
Color precision	Precision	Processed internally. Affects the interpretation of true colors.
Maximum color index	Maximum index	Processed internally. Defines a size of the internal palette.
VDC type	Type	Processed internally. Defines a type of parameters – either integer or float.
Integer precision	Precision	Processed internally. Affects the interpretation of many integer parameters.
Color model	Color model	The only RGB is supported by the ImageGear CGM filter.
Metafile default replacement	Default replacement flag	Processed internally. Turns on the default setting mode.
Begin picture		Defines begin of HIGEAR page.
Begin figure		Starts IG_VECT_ENT_FIGURE entity. All objects being read inside Begin figure/End figure block will be added to the figure entity container.
End figure		Finishes IG_VECT_ENT_FIGURE entity. See above.
Color table	RGB color values	Processed internally. Creates the internal palette.
Aspect source flags	Type Value	Processed internally. Affects the interpretation of different objects and parameters.
Line Width	Width	Specifies a width for HIG_VECT_LINETYPE object.
Line bundle index	Index	Specifies a set of predefined parameters for line objects.
Line type	Type	Specifies a pattern for HIG_VECT_LINETYPE object.
Line color	Color	Specifies IG_VECT_ENT_ATTR_DRAWCOLOR attribute for entities.
Polyline	Vertices	IG_VECT_ENT_POLYLINE entity.
Disjoined polyline	Vertices	IG_VECT_ENT_POLYLINE entity.
Connection edge		IG_VECT_ENT_CONNECTION entity.
Clip rectangle	First corner Second corner	IG_VECT_ENT_VIEWPORT entity.
New region		New region for IG_VECT_ENT_FIGURE entity.
Text bundle index	Index	Specifies a set of predefined parameters for text objects.
Text color	Color	Specifies a color for HIG_VECT_TEXTOBJ object.
Character height	Height	Specifies text height for HIG_VECT_TEXTOBJ object.
Text font index	Index	HIG_VECT_FONT objects.
Character spacing	Spacing	Specifies character spacing for HIG_VECT_TEXTOBJ object.
Character expansion factor	Expansion	Used for calculating the character width for HIG_VECT_TEXTOBJ object.
Restricted text type	Type	Specifies restriction type for IG_VECT_ENT_TEXT entity.
Text alignment	Horizontal alignment Vertical alignment	Specifies an alignment for IG_VECT_ENT_TEXT entity.
Text path	Path	Specifies an orientation of IG_VECT_ENT_TEXT entity.
Character orientation	XUp YUp XBase YBase	Specifies an orientation of characters for HIG_VECT_TEXTOBJ object.
Restricted text	Delta width Delta height Text position Final/not final flag Text string	IG_VECT_ENT_TEXT entity.
Append text	Final/not final flag Text string	IG_VECT_ENT_TEXT entity.
Text	Text position Final/not final flag Text string	IG_VECT_ENT_TEXT entity.
Edge visibility	Visibility	Affects the creation of IG_VECT_ENT_ATTR_DRAWCOLOR and IG_VECT_ENT_ATTR_LINETYPE attributes for entities.
Edge width	Width	Specifies IG_VECT_ENT_ATTR_THICKNESS attribute for entities.
Edge bulge index	Index	Specifies a set of predefined parameters for polygon edges.
Edge type	Type	Specifies a pattern for HIG_VECT_LINETYPE object. Applicable mostly to polylines.
Edge color	Color	Specifies IG_VECT_ENT_ATTR_DRAWCOLOR attribute for entities.
Fill bundle index	Index	Specifies a set of predefined parameters for HIG_VECT_FILLTYPE object.
Interior style	Style	Specifies a pattern for HIG_VECT_FILLTYPE object.
Fill color	Color	Specifies IG_VECT_ENT_ATTR_FILLCOLOR attribute for entities.
Hatch index	Index	Specifies a pattern for HIG_VECT_FILLTYPE object if interior style is a hatch.
Polygon	Vertices	IG_VECT_ENT_POLYLINEEX entity.
Polygon set	Vertices Edge out flags	IG_VECT_ENT_POLYLINEEX entity.
Rectangle	First corner Second corner	IG_VECT_ENT_POLYLINE entity.
Circle	Center Radius	IG_VECT_ENT_ELLIPSE entity.
Circular arc 3 point	Starting point Intermediate point Ending point	IG_VECT_ENT_ARC entity.
Circular arc 3 point close	Starting point Intermediate point Ending point Type of arc closure	IG_VECT_ENT_ARC entity.
Circular arc center	Center Delta x for start vector Delta y for start vector Delta x for end vector Delta y for end vector	IG_VECT_ENT_ARC entity.
Circular arc center close	Center Delta x for start vector Delta y for start vector Delta x for end vector Delta y for end vector Type of arc closure	IG_VECT_ENT_ARC entity.
Ellipse	Center Endpoint of first conjugate diameter Endpoint of second conjugate diameter	IG_VECT_ENT_ELLIPSE entity.
Elliptical arc	Center Endpoint of first conjugate diameter Endpoint of second conjugate diameter Delta x for start vector Delta y for start vector Delta x for end vector Delta y for end vector	IG_VECT_ENT_ARC entity.
Elliptical arc close	Center Endpoint of first conjugate diameter Endpoint of second conjugate diameter Delta x for start vector Delta y for start vector Delta x for end vector Delta y for end vector Type of arc closure	IG_VECT_ENT_ARC entity.
Marker bundle index	Index	Specifies a set of predefined parameters for markers. See Poly Marker section.
Marker type	Type	Specifies predefined type of marker. See Poly Marker section.
Marker size	Size	Specifies size of marker. See Poly Marker section.
Marker color	Color	Specifies color of marker. See Poly Marker section.
Poly Marker	Marker positions	IG_VECT_ENT_BLOCK entity with several entities in its entity container.
Cell array	Corner point P Corner point Q Corner point R Nx Ny Local color precision Array of cell color values	IG_VECT_ENT_RASTER entity.
Begin tile array	Position Path direction Line progression direction Number of tiles in path direction Number of tiles in line direction Number of cells/tile in path direction Number of cells/tile in line direction Cell size in path direction Cell size in line direction Image offset in path direction Image offset in line direction Image number of cells in path direction Image number of cells in line direction	IG_VECT_ENT_BLOCK and IG_VECT_ENT_INSERTION entities. IG_VECT_ENT_INSERTION references IG_VECT_ENT_BLOCK.
Tile	Compression type Supported types: Group4, 1D Group3, 2D Group3, JPEG Not implemented: Null background, null foreground, bitmap, run length, LZW, PNG Row padding indicator Cell color precision Compression-specific parameters Bit stream	IG_VECT_ENT_RASTER entity.
End tile array		Closes “Begin tile array”.
Begin segment	Segment identifier	IG_VECT_ENT_BLOCK entity.
Segment display priority	Segment identifier Priority	Used internally to sort segment blocks in the drawing.
Copy segment	Segment identifier Transformation matrix	IG_VECT_ENT_INSERTION entity that references the block specified by segment identifier.
Polybezier	Continuity indicator Control points	IG_VECT_ENT_BEZIER_CURVE entity.
Non-uniform B-spline	Spline order Number of control points Control points List of knots	IG_VECT_ENT_NURBS_CURVE entity.
Non-uniform rational B-spline	Spline order Number of control points Control points List of knots List of weights	IG_VECT_ENT_NURBS_CURVE entity.
End Picture		Finishes reading the page.
End segment		Closes “Begin segment” element.
End metafile		Finishes reading the file.

ImageGear Vector Entities Supported for Writing to CGM Format

Only the content of active view is saved in CGM format. View content is transformed using view transformation when saving.

ImageGear Entity or Object	Saved as CGM Element
HIG_VECT_VIEW	VDC extent. Begin picture body. End picture body.
IG_VECT_ENT_BLOCK	Sequence of CGM elements for every entity.
IG_VECT_ENT_EASYLINE	Polyline.
IG_VECT_ENT_TEXT	Text, Restricted text, Append text, depending on the entity settings.
IG_VECT_ENT_POLYLINE	Polyline or polygon, depending on the entity settings.
IG_VECT_ENT_INSERTION	Sequence of CGM elements for every entity in the referenced block.
IG_VECT_ENT_RASTER	Cell array.
IG_VECT_ENT_ARC	Circular arc 3 point, Circular arc 3 point close, Elliptical arc, Elliptical arc close, depending on the entity settings.
IG_VECT_ENT_ELLIPSE	Circle or Ellipse, depending on the entity settings.
IG_VECT_ENT_NURBS_CURVE	Non-uniform B-spline or Non-uniform rational B-spline, depending on the entity settings.
IG_VECT_ENT_BEZIER_CURVE	Polybezier.
IG_VECT_ENT_NURBS_SURFACE	The surface is saved as a set of Polyline objects, without interpolation and without taking into account knots and weights.
IG_VECT_ENT_VIEWPORT	Clip rectangle.
IG_VECT_ENT_FIGURE	“Begin Figure”, several “New Region” and “End Figure” objects.
IG_VECT_ENT_CONNECTION	Connecting Edge.
IG_VECT_ENT_POLYLINEEX	Polygon set.
IG_VECT_ENT_EASY_SURFACE	The surface is saved as a set of Polyline objects.
IG_VECT_ENT_SHELL	A set of Polyline or Polygon objects, depending on the entity settings.
FN_IG_ENT_SOLID	Polyline or Polygon object, depending on the entity settings.

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