8.12.3.17 IfcImageTexture

8.12.3.17.1 Semantic definition

An IfcImageTexture provides a 2-dimensional texture that can be applied to a surface of an geometric item and that provides lighting parameters of a surface onto which it is mapped. The texture is provided as an image file at an external location for which an URL is provided.

The following definitions from ISO/IEC 19775-1 X3D Architecture and base components (X3D Specification) apply:

• Greyscale pixels without alpha or simple transparency are treated as intensity textures.
• Greyscale pixels with alpha or simple transparency are treated as intensity plus alpha textures.
• RGB pixels without alpha channel or simple transparency are treated as full RGB textures.
• RGB pixels with alpha channel or simple transparency are treated as full RGB plus alpha textures.
• If the image specifies colours as indexed-colour (that is, palettes or colourmaps), the following semantics should be used (note that `greyscale' refers to a palette entry with equal red, green, and blue values):
• If all the colours in the palette are greyscale and there is no transparency chunk, it is treated as an intensity texture.
• If all the colours in the palette are greyscale and there is a transparency chunk, it is treated as an intensity plus opacity texture.
• If any colour in the palette is not grey and there is no transparency chunk, it is treated as a full RGB texture.
• If any colour in the palette is not grey and there is a transparency chunk, it is treated as a full RGB plus alpha texture.
• Texture nodes that require support for JPEG files shall interpret JPEG files as follows:
• Greyscale files (number of components equals 1) are treated as intensity textures.
• YCbCr files are treated as full RGB textures.
• No other JPEG file types are required. It is recommended that other JPEG files are treated as a full RGB textures.
• Texture nodes that recommend support for GIF files shall follow the applicable semantics described above for the PNG format.

The Uniform Resource Locator (URL) is a form of an URI and specified in RFC1738 by IETF. It supports resources located on a particular server being accessed by a particular protocol (usually http), and resources located at a local machine.

Exchange files following the ifcZIP convention may include a sub directory structure for image resources to be stored together with the product data set. The definitions of texturing within this standard have been developed in dependence on the texture component of X3D. See ISO/IEC 19775-1.2:2008 X3D Architecture and base components Edition 2, Part 1, 18 Texturing component for the definitions in the international standard. New entity in IFC2x2.

8.12.3.17.2 Entity inheritance

1. • IfcPresentationItem
2. • IfcSurfaceTexture
   • IfcColourRgbList
   • IfcColourSpecification
   • IfcCurveStyleFont
   • IfcCurveStyleFontAndScaling
   • IfcCurveStyleFontPattern
   • IfcIndexedColourMap
   • IfcPreDefinedItem
   • IfcSurfaceStyleLighting
   • IfcSurfaceStyleRefraction
   • IfcSurfaceStyleShading
   • IfcSurfaceStyleWithTextures
   • IfcTextStyleForDefinedFont
   • IfcTextStyleTextModel
   • IfcTextureCoordinate
   • IfcTextureVertex
   • IfcTextureVertexList
3. • IfcImageTexture
   • IfcBlobTexture
   • IfcPixelTexture

8.12.3.17.3 Attributes

#	Attribute	Type	Description
IfcSurfaceTexture (7)
1	RepeatS	IfcBoolean	The RepeatS field specifies how the texture wraps in the S direction. If RepeatS is TRUE (the default), the texture map is repeated outside the [0.0, 1.0] texture coordinate range in the S direction so that it fills the shape. If RepeatS is FALSE, the texture coordinates are clamped in the S direction to lie within the [0.0, 1.0] range.
2	RepeatT	IfcBoolean	The RepeatT field specifies how the texture wraps in the T direction. If RepeatT is TRUE (the default), the texture map is repeated outside the [0.0, 1.0] texture coordinate range in the T direction so that it fills the shape. If RepeatT is FALSE, the texture coordinates are clamped in the T direction to lie within the [0.0, 1.0] range.
3	Mode	OPTIONAL IfcIdentifier	Mode shall hold the type of map this corresponds to, chosen from the following list: AMBIENT, NORMAL, EMISSIVE, METALLICROUGHNESS, OCCLUSION, SHININESS, SPECULAR, DIFFUSE. If Mode is omitted, DIFFUSE is assumed. New attribute replacing previous TextureType. Attribute has been repurposed to store the type of texture.
4	TextureTransform	OPTIONAL IfcCartesianTransformationOperator2D	The TextureTransform defines a 2D transformation that is applied to the texture coordinates. It affects the way texture coordinates are applied to the surfaces of geometric representation items. The 2D transformation supports changes to the size, orientation, and position of textures on shapes. Mirroring is not allowed to be used in the IfcCartesianTransformationOperator
5	Parameter	OPTIONAL LIST [1:?] OF IfcIdentifier	This attribute is deprecated and shall no longer be used.
	IsMappedBy	SET [0:?] OF IfcTextureCoordinate FOR Maps	Texture coordinates, either provided by a corresponding list of texture vertices to vertex-based geometric items or by a texture coordinate generator, that applies the surface texture to the surfaces of the geometric items. New attribute added at the end of the attribute list.
	UsedInStyles	SET [0:?] OF IfcSurfaceStyleWithTextures FOR Textures	No description available.
Click to show 7 hidden inherited attributes Click to hide 7 inherited attributes
IfcImageTexture (1)
6	URLReference	IfcURIReference	Location, provided as an URI, at which the image texture is electronically published.

8.12.3.17.4 Examples

• 

  Tessellation With Image Texture

8.12.3.17.5 Formal representation

ENTITY IfcImageTexture
 SUBTYPE OF (IfcSurfaceTexture);
	URLReference : IfcURIReference;
END_ENTITY;

8.12.3.17.6 References

• IfcSurfaceTexture