IfcFillAreaStyleHatching

Definition from ISO/CD 10303-46:1992: The fill area style hatching defines a styled pattern of curves for hatching an annotation fill area or a surface.

Definition from IAI: The IfcFillAreaStyleHatching is used to define simple, vector-based haching patterns, based on styled straight lines. The curve font, color and thickness is given by the HatchLineAppearance, the angle by the HatchLineAngle and the distance to the next hatch line by StartOfNextHatchLine, being either an offset distance or a vector.

NOTE  If the hatch pattern involves two (potentially crossing) rows of hatch lines, then two instances of IfcFillAreaStyleHatching should be assigned to the IfcFillAreaStyle. Both share the same (virtual) point of origin of the hatching that is used by the reference hatch line (or the PointOfReferenceHatchLine if there is an offset).

For better control of the hatching appearance, when using hatch lines with other fonts then continuous, the PatternStart allows to offset the start of the curve font pattern along the reference hatch line (if not given, the PatternStart is at zero distance from the virtual point of origin). If the reference hatch line does not go through the origin (of the virtual hatching coordinate system), it can be offset by using the PointOfReferenceHatchLine.

NOTE  The coordinates of the PatternStart and the PointOfReferenceHatchLin are given relative to the assumed 0., 0. virtual point of origin at which the hatch pattern is later positioned by the FillStyleTarget point at IfcAnnotationFillAreaOccurrence.  The measure values are given in global drawing length units and apply to the target plot scale for the scale depended representation subcontext.

Illustration

	Fig.1 simple hatching given by using a curve font "continuous" at HatchLineAppearance. The distance of hatch lines is given by a positive length measure. The angle (here 45' if measures in degree) is provided by HatchLineAngle. The PatternStart and the PointOfReferenceHatchLine are set to NIL ($) in this example.		Fig. 2 hatching from figure 1 with using a different curve font at HatchLineAppearance. The distance of hatch lines is given by a positive length measure, therefore the font pattern start is at a point at the next hatch line given by a vector being perpendicular to the point of origin at the reference hatch line. The PatternStart and the PointOfReferenceHatchLine are set to NIL ($) in this example.
	Fig. 3 hatching from figure 2 with using a vector to determine the pattern start of the next hatch lines. The pattern start is the beginning of the first visual curve font pattern segment at IfcCurveFont. CurveFont. The PatternStart and the PointOfReferenceHatchLine are set to NIL ($) in this example.		Fig. 4 hatching from figure 3 where the pattern start is offset from the point of origin at the reference hatch line. I.e. the first visible curve font pattern segment now does not start at the point of origin at the reference hatch line. The PointOfReferenceHatchLine is set to NIL ($) in this example.
	Fig. 5 hatching from figure 4 where the hatch pattern is shifted against the underlying coordinate system. The point that is mapped to the insertion point of the IfcAnnotationFillAreaOccurrence now has an x and y offset from the start of the reference hatch line. I.e. the reference hatch line now does not go through the insertion point of the hatching.

NOTE  Corresponding STEP name: fill_area_style_hatching. Please refer to ISO/IS 10303-46:1994, p. 108 for the final definition of the formal standard.

HISTORY  New entity in Release IFC2x Edition 2.
IFC2x Edition 3 CHANGE  The IfcFillAreaStyleHatching has been changed by making the attributes PatternStart and PointOfReferenceHatchLine OPTIONAL. The attribute StartOfNextHatchLine has changed to a SELECT with the additional choice of IfcPositiveLengthMeasure. Upward compatibility for file based exchange is guaranteed.

EXPRESS specification:

Attribute definitions:

Formal Propositions:

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