[Top] [Prev] [Next] [Bottom]

5.8 Graphic Representation Modules

Each vector based object in the SDTS transfer except Ring can include a foreign identifier that references a representation module. The representation module reference determines how the object should be portrayed within fixed product scale ranges (i.e., scale ranges, Small Scale Minimum and Large Scale Maximum, are given in the appropriate subfields for this module).

The parameters associated with the representation module indexed by the foreign identifier determine the values used by graphical devices to produce a display or plot. The Computer Graphics Metafile (CGM) standard provides a device-independent format for the transmission of picture description data. The SDTS standard and the CGM standard (ANSI X3.122-1986) follow the same formats for definition of the graphical representation of an object. To support cartographic spatial applications, several parameters have been modified to present parameters in a standard form used by cartographers. The content is the same and the format differences are clearly noted. CGM must be used as the reference for the modules.

The graphic representation modules include the following:

	Text Representation
	Line Representation
	Symbol Representation
	Area Fill Representation
	Color Index
	Font Index

Table 45 relates the module type with the representation code and lists the types of objects that reference the module type.

The Register of Graphical Items (see 1.3.16) may also be used to support the Line, Symbol, and Area Fill graphical representation modules.

The representation modules use an index into the Color and Font Index modules. These modules reference primitive graphics elements defined by a registration authority, such as the one for CGM or defined explicitly in a Data Dictionary/Domain module. For complex graphic representations, the formats may be transmitted using a separate SDTS transfer that includes a graphic representation for each symbol or line representation option. The authority must then be the associated transfer modules.

5.8.1 Text Representation Module

The Text Representation module provides the graphic data necessary to portray the text (see Table 46).

Necessary parameters are included to define the placement of text independently of device functionality. Parameters such as text precision, which is in the CGM standard, must be determined by the product requirements and device capabilities of the receiving system. The CGM standard uses a character orientation vector that encodes character height, skew angle, and orientation in a CGM-defined coordinate system. SDTS specifies the same parameters at a base geographic scale. These parameters can be directly converted to the CGM character orientation vector (see Figure 28).

The font coordinate system is illustrated in Figure 28 - Text Definition Parameters. The character body encloses all of the drawn parts (kerning excepted) of all characters in the font (that is, no descender extends lower than the bottom and no accent or oversized symbol extends higher than the top). The left and right edges of the character body may be defined on a per character basis to accomodate variable width and proportional spacing. It is expected that some font designers will specify fonts having kerns beyond the character body. The body exceeds the actual character symbol width and height as necessary to provide adequate white space between characters, so that text is readable and adequately separated when the character spacing is zero. The character height is the height of the character at the base scale. For different scale products the character should be scaled inversely with the scale factor. The character expansion factor specifies the deviation of the width to height of the characters from the ratio indicated by the font designer. If the value of the character spacing is positive, additional space is inserted between character bodies. If negative, adjacent character bodies overlap although the charactor symbols themselves might not. The character height is specified as a fraction of the scaled character heigth.

The text path and the horizontal and vertical text alignment parameters specify how the string is aligned relative to the label point and the orientation points. The skew angle is the angle between the base vector and the character up arrow.

5.8.2 Line Representation Module

The Line Representation module (see Table 47) provides the graphic data necessary to portray one-dimensional spatial objects (see Figure 28).

The standard line representation repertoire is not sufficient for most cartographic applications. To use a line type outside the defined domain, the SDTS user must identify the application's representation requirements, assign line types to these representations, and fully define the representations in a Data Dictionary/Domain module. The definition must include precise lengths, symbol references, and other requirements.

5.8.3 Symbol Representation Module

The Symbol Representation module (see Table 48) provides the graphic data necessary to portray the symbols.

The standard symbol representation repertoire is not sufficient for most cartographic applications. To use a symbol marker outside the defined domain, the SDTS user must identify the application's requirements, assign marker types to these representations, and fully define the representations in the Data Dictionary.

5.8.4 Area Fill Representation Module

The Area Fill representation module provides the graphic data necessary to fill polygonal areas (see Table 49).

The representation of the edge of a polygon is defined by its associated linear objects.

5.8.5 Color Index Module

The Color Index module (see Table 50) provides the correlation between a color index value and specific normalized values for the red, green, and blue components of the desired color. Color values are a 3-tuple of values providing the normalized weight of red, green, and blue components. Each component of the 3-tuple is normalized to the continuous range of real numbers [0,1]. For any given component, one end of the range indicates that none of that component is included, and the other end indicates the maximum intensity of that component.

For color process printing, magenta, cyan, and yellow values are combined with a black intensity to fully define the color to be printed. The values or magenta, cyan, and yellow may be determined by the following equations:

	magenta component =1. - green component;
	cyan component  =1. - red component; and
	yellow component  =1. - blue component.

The Color Index module also provides an optional Black Intensity Component to provide the black intensity to complete the process color definition. If the Black Intensity Component is omitted, a default value of zero is assumed.

5.8.6 Font Index Module

The Font Index module (see Table 51) provides the correlation between a font index value and a font defined in the Data Dictionary.

Table 45 - Representation module type and object representations

Module type	Object representations	Object type
Text	NL	Label Point
Line	LS	String
	LQ	Link
	LE	Complete Chain
	LL	Area Chain
	LW	Network Chain (planar graph)
	LY	Network Chain (nonplanar graph)
	AC	Circular arc, three point center
	AE	Elliptical arc
	AU	Uniform B-spline
	AB	Piecewise Bezier
Symbols (points)	NP	Point
	NE	Entity point
	NA	Area point
	NO	Node, planar graph
	NN	Node, network
Area fill	PG	G-polygon
	PR	GT-polygon composed of rings
	PC	GT-polygon composed of chains
	PU	Universe polygon composed of rings
	PW	Universe polygon composed of chains
	PV	Void polygon composed of rings
	PX	Void polygon composed of chains

Table 46 - Text representation module specification

FIELD NAME	SUBFIELD NAME	FIELD/SUBFIELD DESCRIPTION	TYPE	DOMAIN	DOMAIN DESCRIPTION	MNEMONIC
Text Representation (P) [M]						TEXT
	Module Name [M]	A unique identifier for this Text Representation module.	A	Alphanum	Name must begin with an alphabetic character other than SPACE.	MODN
	Record ID [M]	A number for the module record, unique within the module.	I	Integer	An unsigned integer unique within the representation module. With Module Name must form unique ID within the file set.	RCID
	Base Scale [M]	The scale denominator used to translate the scale-independent data transferred in the SDTS transfer to scale-dependent graphic attributes such as text height.	I	Integer	A valid numeric scale denominator.	BSCL
	Small Scale Minimum	The smallest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	SSCL
	Large Scale Maximum	The largest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	LSCL
	Color Index [M]	Index corresponding to a value of the Record ID subfield in the Color Index module.	I	Integer	Unsigned integer.	CLDX
	Character Height [M]	Specifies the distance measured in millimeters between the capline and the baseline of the font for the graphics portrayal of the spatial data at the base scale.	R	Real	Character height measured in millimeters.	CHHT
	Font Index [M]	Index corresponding to a value of the Record ID subfield in the Font Index module.	I	Integer	Unsigned integer.	FTDX
	(d)Text Path	Specifies the writing direction of the text string. Path directions are right, left, up, or down. Right is assumed if text path is not explicitly included.	A	RIGHT LEFT UP DOWN	Right. Left. Up. Down.	TPTH
	(d)Horizontal Text Alignment	Controls the positioning of the text extent rectangle in relation to the text position. The horizontal text alignment has three possible values: "left," "center," and "right." For example, if the horizontal text alignment is "left," the left side of the text extent rectangle passes through the text position. Left is assumed if horizontal text alignment is not explicitly included.	A	LEFT CENTER RIGHT	Left. Center. Right.	UTXA
	(d)Vertical Text Alignment	Controls the positioning of the text extent rectangle in relation to the text position. The vertical text alignment has five possible values: "top," "cap," "half," "base," and "bottom." The vertical alignment causes the text to be moved in such a way that the corresponding defining line of the text extent rectangle passes through the text position. Base is assumed if vertical text alignment is not explicitly included. Note that the values specified for the horizontal and vertical text alignment are a subset of those required by the CGM for the CGM text alignment vector.	A	TOP CAP HALF BASE BOTTOM	Top. Cap. Half. Base. Bottom.	VTXA
	(d)Character Expansion Factor	Specifies the deviation of the width to height ratio of the characters from the ratio indicated by the font designer. A value of one is assumed if the factor is not explicitly included.	R	Real	The deviation of the width to height ratio of the characters from the ratio indicated by the font designer.	CHEX
	(d)Character Spacing	Specifies how much additional space is to be inserted between adjacent character bodies. Character spacing is specified as fraction of character height. Zero is assumed if not explicitly defined.	R	Real	Space to be inserted between adjacent character bodies.	CHSP
	(d)Skew Angle [O]	Specifies the skew angle of the characters. The skew angle is the angle between the character base vector and the character up vector. It represents the slant angle of the characters. The value is measured in decimal degrees with 90 assumed unless otherwise specified. Skew angle values near 0 or 180 should be avoided since the result is likely to be unreadable or not visible.	R	Real	Measured in decimal degrees between 0 and 180.	SANG
(continued)

Table 47 - Line Representation module specification

FIELD NAME	SUBFIELD NAME	FIELD/SUBFIELD DESCRIPTION	TYPE	DOMAIN	DOMAIN DESCRIPTION	MNEMONIC
LineRepresentation (P) [M]						LNRP
	Module Name [M]	A unique identifier for this Line Representation module.	A	Alphanum	Name must begin with an alphabetic character other than SPACE.	MODN
	Record ID [M]	A number for the module record, unique within the module.	I	Integer	An unsigned integer unique within the representation module. With Module Name must form unique ID within the file set.	RCID
	Base Scale [M]	The scale denominator used to translate the scale independent data transferred in the SDTS transfer to scale dependent graphic attributes such as dash spacing.	I	Integer	A valid numeric scale denominator.	BSCL
	Small Scale Minimum	The smallest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	SSCL
	Large Scale Maximum	The largest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	LSCL
	Color Index [M]	Index corresponding to a value of the Record ID subfield in the Color Index module.	I	Integer	Unsigned integer.	CLDX
	Line Type [M]	The type of line representation. Values above 5 are reserved for extensions and future standardization. Negative values are available for implementation dependent use, with definitions given in corresponding Data Dictionary/Domain module.	I	1	Solid line.	LTYP
				2	Dashed line.
				3	Dotted line.
				4	Dash-dot line.
				5	Dash-dot-dot line.
				dd: >5	Reserved for extension.
				dd: <=0	Implementation dependent.
	Line Width	The line width measured in millimeters at the base scale. If not specified, the receiving system should use the smallest visible line width.	R	Real	The line width measured in millimeters.	LWTH

Table 48 - Symbol representation module specification

FIELD NAME	SUBFIELD NAME	FIELD/SUBFIELD DESCRIPTION	TYPE	DOMAIN	DOMAIN DESCRIPTION	MNEMONIC
SymbolRepresentation (P) [M]						SYRP
	Module Name [M]	A unique identifier for this Symbol Representation module.	A	Alphanum	Name must begin with an alphabetic character other than SPACE.	MODN
	Record ID [M]	A number for the module record, unique within the module.	I	Integer	An unsigned integer unique within the representation module. With Module Name must form unique ID within the file set.	RCID
	Base Scale [M]	The scale denominator used to translate the scale independent data transferred in the SDTS transfer to scale dependent graphic attributes such as symbol height.	I	Integer	A valid numeric scale denominator.	BSCL
	Small Scale Minimum	The smallest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	SSCL
	Large Scale Maximum	The largest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	LSCL
	Color Index [M]	Index corresponding to a value of the Record ID subfield in the Color Index module.	I	Integer	Unsigned integer.	CLDX
	Symbol Marker Type [M]	The type of symbol representation. Values above 5 are reserved for extensions and future standardization. Negative values are available for implementation dependent use, with definitions given in corresponding Data Dictionary/Domain module.	I	1	Dot	SMKR
				2	Plus
				3	Asterick
				4	Circle
				5	Diagonal cross
				dd:>5	Reserved for future extensions.
				dd:<=0	Implementation dependent.
	Marker Size [M]	The symbol measured in millimeters at the base scale.	R	Real	The symbol height measured in millimeters.	MKSZ

Table 49 - Area fill representation module specification

FIELD NAME	SUBFIELD NAME	FIELD/SUBFIELD DESCRIPTION	TYPE	DOMAIN	DOMAIN DESCRIPTION	MNEMONIC
Area Fill Representation (P) [M]						AFIL
	Module Name [M]	A unique identifier for this Area Fill Representation module.	A	Alphanum	Name must begin with an alphabetic character other than SPACE.	MODN
	Record ID [M]	A number for the module record, unique within the module.	I	Integer	An unsigned integer unique within the module. With Module Name must form unique ID within the file set.	RCID
	Base Scale [M]	The scale denominator used to translate the scale independent data transferred in the SDTS transfer to scale dependent graphic attributes such as symbol height.	I	Integer	A valid numeric scale denominator.	BSCL
	Small Scale Minimum	The smallest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	SSCL
	Large Scale Maximum	The largest appropriate scale denominator for the graphics representation.	I	Integer	A valid numeric scale denominator.	LSCL
	Color Index [M/Fill Style Type = HOLLOW|SOLID|HATCH|PATTERN]	Index corresponding to a value of the Record ID subfield in the Color Index module.	I	Integer	Unsigned integer.	CLDX
	Fill Style Type [M]	The interior fill style may be "hollow," "solid," "pattern," "hatch," or "empty." Additional index values must be defined in the Data Dictionary/Domain module.	A	HOLLOW	No filling, but the bounding line of the filled area is drawn using the fill color currently selected. The boundary of a HOLLOW filled area is the representation of the interior. The bounding line is distinct from the edge and is drawn only for HOLLOW filled areas.	FTYP
				SOLID	Fill the interior using the fill color.
				PATTERN	Fill the interior using the pattern index defined pattern
				HATCH	Fill the interior using the fill color and the hatch index.
				EMPTY	No filling is done and no boundary is drawn, i.e., nothing is done to represent the interior.
				dd: if not listed above	Additional values defined in a Data Dictionary/Domain module.
	Hatch Index [M]	Hatch index value. Values above 6 are reserved for registration and future standardization. Negative values are available for implementation dependent use, with definitions given in corresponding Data Dictionary/Domain module.	I	1	Horizontal equally spaced parallel lines.	HIDX
				2	Vertical equally spaced parallel lines.
				3	Positive slope equally spaced parallel lines.
				4	Negative slope equally spaced parallel lines.
				5	Horizontal/vertical crosshatch.
				6	Positive slope/negative slope crosshatch.
				dd:>6	Reserved for registration.
				dd:<=0	Implementation dependent.
	Pattern Index [M]	An integer value that defines the type of pattern. Values for this index must be defined in a Data Dictionary/Domain module.	I	Integer	An integer value that defines the type of pattern.	PIDX

Table 50 - Color index module specification

FIELD NAME	SUBFIELD NAME	FIELD/SUBFIELD DESCRIPTION	TYPE	DOMAIN	DOMAIN DESCRIPTION	MNEMONIC
Color Index (P) [M]						CLRX
	Module Name [M]	A unique identifier for this Color Index module.	A	Alphanum	Name must begin with an alphabetic character other than SPACE.	MODN
	Record ID [M]	A number for the module record, unique within the module.	I	Integer	An unsigned integer unique within the representation module. With Module Name must form unique ID within the file set.	RCID
	Red Component [M]	The red component of the desired color normalized from zero to one.	R	Real	The red component of the desired color normalized from zero to one.	RED
	Green Component [M]	The green component of the desired color normalized from zero to one.	R	Real	The green component of the desired color normalized from zero to one.	GREN
	Blue Component [M]	The blue component of the desired color normalized from zero to one.	R	Real	The blue component of the desired color normalized from zero to one.	BLUE
	Black Intensity Component	The black intensity component normalized from zero to one.	R	Real	The black intensity component normalized from zero to one.	BLCK

Table 51 - Font index module specification

FIELD NAME	SUBFIELD NAME	FIELD/SUBFIELD DESCRIPTION	TYPE	DOMAIN	DOMAIN DESCRIPTIOn	MNEMONIC
Font Index (P) [M]						FONT
	Module Name [M]	A unique identifier for this Font Index module.	A	Alphanum	Name must begin with an alphabetic character other than SPACE.	MODN
	Record ID [M]	A number for the module record, unique within the module.	I	Integer	An unsigned integer unique within the representation module. With Module Name must form unique ID within the file set.	RCID
	Font [M]	The name or index of the actual font.	I|A	Integer Alphanum	Font number or font name Format defined in a Data Dictionary/Domain module.	FNTN