EN ISO/ASTM 52915:2017

SLOVENSKI STANDARD
01-maj-2017
6SHFLILNDFLMD]DDGLWLYQRSURL]YRGQMRIRUPDWD$0)UD]OLþLFD,62$670

Specification for Additive Manufacturing File Format (AMF) Version 1.2 (ISO/ASTM
52915:2016)
Spezifikation für ein Dateiformat für Additive Fertigung (AMF) Version 1.2 (ISO/ASTM
52915:2016)
Spécification normalisée pour le format de fichier pour la fabrication additive (AMF)
Version 1.2 (ISO/ASTM 52915:2016)
Ta slovenski standard je istoveten z: EN ISO/ASTM 52915:2017
ICS:
25.030 3D-tiskanje Additive manufacturing
35.240.50 Uporabniške rešitve IT v IT applications in industry
industriji
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO/ASTM 52915
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2017
EUROPÄISCHE NORM
ICS 25.030; 35.240.50
English Version
Specification for additive manufacturing file format (AMF)
Version 1.2 (ISO/ASTM 52915:2016)
Spécification normalisée pour le format de fichier pour Spezifikation für ein Dateiformat für Additive
la fabrication additive (AMF) Version 1.2 (ISO/ASTM Fertigung (AMF) Version 1.2 (ISO/ASTM 52915:2016)
52915:2016)
This European Standard was approved by CEN on 17 January 2017.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO/ASTM 52915:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO/ASTM 52915:2016 has been prepared by Technical Committee ISO/TC 261 “Additive
manufacturing” of the International Organization for Standardization (ISO) and has been taken over as
secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by August 2017, and conflicting national standards shall
be withdrawn at the latest by August 2017.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO/ASTM 52915:2016 has been approved by CEN as EN ISO/ASTM 52915:2017 without
any modification.
INTERNATIONAL ISO/ASTM
STANDARD 52915
Second edition
2016-02-15
Specification for Additive
Manufacturing File Format (AMF)
Version 1.2
Spécification normalisée pour le format de fichier pour la fabrication
additive (AMF) Version 1.2
Reference number
ISO/ASTM 52915:2016(E)
©
ISO/ASTM International 2016
ISO/ASTM 52915:2016(E)
© ISO/ASME International 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester. In the United States, such requests should be sent to ASTM International.
ISO copyright office ASTM International
Ch. de Blandonnet 8 • CP 401 100 Barr Harbor Drive, PO Box C700
CH-1214 Vernier, Geneva, Switzerland West Conshohocken, PA 19428-2959, USA
Tel. +41 22 749 01 11 Tel. +610 832 9634
Fax +41 22 749 09 47 Fax +610 832 9635
copyright@iso.org khooper@astm.org
www.iso.org www.astm.org
ii © ISO/ASTM International 2016 – All rights reserved

ISO/ASTM 52915:2016(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Key considerations . 2
3.1 General . 2
3.2 Guidelines for the inclusion of future new elements . 3
4 Structure of this specification .3
5 General structure .4
6 Geometry specification .5
6.1 General . 5
6.2 Smooth geometry . 6
6.3 Restrictions on geometry . 7
7 Material specification .7
7.1 General . 7
7.2 Mixed and graded materials and substructures . 9
7.3 Porous materials . 9
7.4 Stochastic materials .10
8 Colour specification.10
8.1 General .10
8.2 Colour gradations and texture mapping .11
8.3 Transparency .12
9 Texture specification .12
10 Constellations .12
11 Metadata .13
12 Compression and distribution .13
13 Minimal implementation .14
Annex A (informative) AMF XML schema implementation guide .15
Annex B (informative) Performance data and future features .23
Bibliography .26
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ISO/ASTM 52915:2016(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 261, Additive manufacturing, in cooperation
with ASTM F 42.91, Terminology, on the basis of a partnership agreement between ISO and ASTM
International with the aim to create a common set of ISO/ASTM standards on Additive Manufacturing.
This second edition cancels and replaces the first edition (ISO/ASTM 52915:2013), which has been
technically revised. This revision contains changes to normative language and details of a minimum
implementation, as well as corrections and clarifications.
iv © ISO/ASTM International 2016 – All rights reserved

ISO/ASTM 52915:2016(E)
Introduction
This International Standard describes an interchange format to address the current and future needs
of additive manufacturing technology. For the last three decades, the stereolithography (STL) file
format has been the industry standard for transferring information between design programs and
additive manufacturing equipment. An STL file defines only a surface mesh and has no provisions
for representing colour, texture, material, substructure and other properties of the fabricated object.
As additive manufacturing technology is evolving quickly from producing primarily single-material,
homogeneous objects to producing geometries in full colour with functionally-defined gradations of
materials and microstructures, there is a growing need for a standard interchange file format that can
support these features.
The Additive Manufacturing File Format (AMF) has many benefits. It describes an object in such
a general way that any machine can build it to the best of its ability, and as such is technology
independent. It is easy to implement and understand, scalable and has good performance. Crucially, it
is both backwards compatible, allowing any existing STL file to be converted, and future compatible,
allowing new features to be added as advances in technology warrant.
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INTERNATIONAL STANDARD ISO/ASTM 52915:2016(E)
Specification for Additive Manufacturing File Format
(AMF) Version 1.2
1 Scope
This International Standard provides the specification for the Additive Manufacturing File Format (AMF),
an interchange format to address the current and future needs of additive manufacturing technology.
The AMF may be prepared, displayed and transmitted provided the requirements of this specification
are met. When prepared in a structured electronic format, strict adherence to an extensible markup
[1]
language (XML) schema is required to support standards-compliant interoperability.
A W3C XML schema definition (XSD) for the AMF is available from ISO from http://standards.iso.
org/iso/52915 and from ASTM from www.astm.org/MEETINGS/images/amf.xsd. An implementation
guide for such an XML schema is provided in Annex A.
It is recognized that there is additional information relevant to the final part that is not covered by the
current version of this International Standard. Suggested future features are listed in Annex B.
This International Standard does not specify any explicit mechanisms for ensuring data integrity,
electronic signatures and encryptions.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
AMF consumer
software reading (parsing) the Additive Manufacturing File Format (AMF) file for fabrication,
visualization or analysis
Note 1 to entry: AMF files are typically imported by additive manufacturing equipment, as well as viewing,
analysis and verification software.
2.2
AMF editor
software reading and rewriting the Additive Manufacturing File Format (AMF) file for conversion
Note 1 to entry: AMF editor applications are used to convert an AMF from one form to another, for example,
convert all curved triangles to flat triangles or convert porous material specification into an explicit mesh surface.
2.3
AMF producer
software writing (generating) the Additive Manufacturing File Format (AMF) file from original
geometric data
Note 1 to entry: AMF files are typically exported by computer-aided design (CAD) software, scanning software or
directly from computational geometry algorithms.
2.4
attribute
characteristic of data, representing one or more aspects or descriptors of the data in an element
Note 1 to entry: In the XML framework, attributes are characteristics of elements.
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ISO/ASTM 52915:2016(E)
2.5
comments
all text elements associated with any data within the Additive Manufacturing File Format (AMF) to be
ignored by import software
Note 1 to entry: Comments are used for enhancing human readability of the file and for debugging purposes.
2.6
element
information unit within an XML document consisting of a start tag, an end tag, the content between the
tags and any attributes
Note 1 to entry: In the XML framework, an element can contain data, attributes and other elements.
2.7
extensible markup language
XML
standard from the WorldWideWeb Consortium (W3C) that provides for tagging of information content
within documents offering a means for representation of content in a format that is both human and
machine readable
Note 1 to entry: Through the use of customizable style sheets and schemas, information can be represented in a
uniform way, allowing for interchange of both content (data) and format (metadata).
[SOURCE: ISO/ASTM 52900:2015, 2.4.7]
2.8
STL
stereolithography
file format for model data describing the surface geometry of an object as a tessellation of triangles
used to communicate 3D geometries to machines in order to build physical parts
Note 1 to entry: The STL file format was originally developed as part of the CAD package for the early
stereolithography apparatus, thus referring to that process. It is sometimes also described as “Standard
Triangulation Language” or “Standard Tessalation Language”, though it has never been recognized as an official
standard by any standardization organization.
[SOURCE: ISO/ASTM 52900:2015, 2.4.16]
3 Key considerations
3.1 General
3.1.1 There is a natural trade-off between the generality of a file format and its usefulness for a specific
purpose. Thus, features designed to meet the needs of one community may hinder the usefulness of a file
format for other uses. To be successful across the field of additive manufacturing, the file format described
in this International Standard, the AMF, is designed to address the concerns listed in 3.1.2 to 3.1.7.
3.1.2 Technology independence. The AMF describes an object in such a general way that any machine
can build it to the best of its ability. It is resolution and layer-thickness independent and does not contain
information specific to any one manufacturing process or technique. This does not negate the inclusion
of features that describe capabilities that only certain advanced machines support (for example, colour,
multiple materials), but these are defined in such a way as to avoid exclusivity.
3.1.3 Simplicity. The AMF is easy to implement and understand. The format can be read and debugged
in a simple text viewer to encourage comprehension and adoption. Identical information is not stored in
multiple places.
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ISO/ASTM 52915:2016(E)
3.1.4 Scalability. The file size and processing time scales well with the increase in part complexity
and with the improving resolution and accuracy of manufacturing equipment. This includes being able
to handle large arrays of identical objects, complex periodic internal features (for example, meshes and
lattices) and smooth curved surfaces when fabricated with very high resolution.
3.1.5 Performance. The AMF enables reasonable duration (interactive time) for read-and-
write operations and reasonable file sizes for a typical large object. Detailed performance data are
provided in Annex B.
3.1.6 Backwards compatibility. Any existing STL file can be converted directly into a valid AMF file
without any loss of information and without requiring any additional information. AMF files are also
easily converted back to STL for use on legacy systems, although advanced features will be lost. This
format maintains the triangle-mesh geometry representation to take advantage of existing optimized
slicing algorithms and code infrastructure already in existence.
3.1.7 Future compatibility. To remain useful in a rapidly changing industry, this file format is easily
extensible while remaining compatible with earlier versions and technologies. This allows new features
to be added as advances in technology warrant, while still working flawlessly for simple homogeneous
geometries on the oldest hardware.
3.2 Guidelines for the inclusion of future new elements
3.2.1 Any new element proposed shall be applicable across all hardware platforms and technologies
that could conceivably be used to generate the desired outcome.
3.2.2 In support of the consideration above, new elements proposed for this International Standard
shall describe the final object, not how to build it. For instance, a hypothetical future element
might be allowed to tell an additive manufacturing system to leave the volume empty if possible.
However, an element that describes how to build a hollow volume shall
not be included since it assumes a particular fabrication process.
4 Structure of this specification
4.1 Format. Information specified throughout this specification is stored in XML 1.0 format. XML is a
text file comprising a list of elements and attributes. Using this widely accepted data format allows for
the use of many tools for creating, viewing, manipulating, parsing and storing AMF files. XML is human-
readable, which makes debugging errors in the file possible. XML can be compressed or encrypted or
both if desired in a post-processing step using highly optimized standardized routines.
4.2 Flexibility. Another significant advantage of XML is its inherent flexibility. Missing or additional
parameters do not present a problem for a parser as long as the document conforms to the XML standard.
Practically, the use of XML namespaces allows new features to be added without breaking old versions of
the parser, such as in legacy software.
4.3 Precision. This file format is agnostic as to the precision of the representation of numeric values.
It is the responsibility of the generating program to write as many or as few digits as are necessary for
proper representation of the target object. However, an AMF consumer should read and process real
numbers in double precision (64 bits).
4.4 Future amendments and additions. While additional XML elements can be added provisionally
to any AMF file for internal purpose, such additions shall not be considered part of this specification. An
unofficial AMF element may be ignored by any AMF consumer and may not be stored or reproduced by an
editor application. An element becomes official only when it is formally accepted into this specification.
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ISO/ASTM 52915:2016(E)
5 General structure
5.1 The AMF file shall begin with the XML declaration line specifying the XML version and
encoding, for example:

The XML version shall be 1.0. Only UTF-8 and UTF-16 should be specified. Unrecognized encodings
should cause the file to fail to load.
5.2 Whitespace characters and standard XML comments may be interspersed in the file and shall be
ignored by any interpreter, for example:

5.3 The remainder of the file shall be enclosed between start and end element tags.
This element denotes the file type and fulfils the requirement that all XML files have a single root element.
A version attribute denoting the version of the AMF standard the file is compliant with should be used.
Standard XML namespace attributes may also be used, such as the lang attribute designed to identify
the natural human language used. The unit system may also be specified (millimetre, inch, foot, metre or
micron). In the absence of a unit specification, the attribute value millimetres is assumed, for example:
xmins:amf=“www.astm.org/Standards/F2915-14”>
5.4 Enclosed within the element start- and end-tags, there are five top level elements, as
described in 5.4.1 to 5.4.5.
5.4.1 The object element defines a volume or volumes of material, each of which might also
reference a material identifier (ID) for AM processing. The object element shall also declare an object ID,
which shall be unique. At least one object element shall be present in the file. Additional objects are optional.
5.4.2 The optional material element defines one material for fabrication, each of which
declares an associated material ID. The material ID declared shall be unique and shall not be 0. If no
material element is included, a single default material is assumed.
5.4.3 The optional texture element defines one image or texture for colour or texture
mapping, each of which declares an associated texture ID. The texture ID declared shall be unique.
5.4.4 The optional constellation element hierarchically combines objects and
other constellations into a relative pattern for printing. The constellation element may also declare an
object ID, which shall be unique. If no constellation elements are specified, each object element shall be
imported with no relative position data. The consumer software may determine the relative positioning
of the objects if more than one object is specified in the file.
5.4.5 The optional metadata element specifies additional information about the
object(s) and elements contained in the file.
5.5 Only a single object element is required for a fully functional AMF file.
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6 Geometry specification
6.1 General
6.1.1 The top level element declares a unique ID and shall contain one child
element. The element shall contain two child elements: and . The
element may optionally reference a material.
6.1.2 The required element shall contain all vertices that are used in this object. Each
vertex is implicitly assigned an identifying integer in the order in which it is declared, starting at zero and
increasing monotonically. The required child element gives the position of the vertex
in three-dimensional (3D) space using the , and child elements.
6.1.3 After the vertex information, at least one element shall be included. Each volume
encapsulates a closed volume of the object. Multiple volumes may be included in a single object. Volumes
may share vertices at interfaces but shall not have any overlapping volume.
6.1.4 Within each volume, multiple child elements shall be used to define the triangles
that tessellate the surface of the volume. Each element shall reference three vertices from
the set of indices of the previously defined vertices. The indices of the three vertices of the triangles shall
be specified using the , and child elements. The vertices shall be ordered according to
the right-hand rule such that vertices are listed in counter-clockwise order as viewed from the outside
of the volume. Each triangle is implicitly assigned an identifying integer in the order in which it was
declared starting at zero and increasing monotonically (see Figure 1).
6.1.5 The geometry shall not be used to describe support structure. Only the final target structure shall
be described.
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ISO/ASTM 52915:2016(E)
NOTE The figure shows a basic AMF file containing only a list of vertices and triangles. This structure is
compatible with the STL standard and can be readable by a minimal implementation of an AMF consumer.
Figure 1 — Basic AMF file
6.2 Smooth geometry
6.2.1 By default, all triangles shall be assumed to be flat and all triangle edges shall be assumed to be
straight lines connecting their two vertices. However, curved triangles and curved edges may optionally
be specified to reduce the number of mesh elements required to describe a curved surface. Minimal AMF
consumer software (see Clause 13) may ignore curvature information associated with triangles.
6.2.2 During import, a curved triangle patch shall be recursively subdivided into four triangles to
generate a final temporary set of flat triangles. The depth of recursion shall be exactly five (that is, a
single curved triangle will be converted into 1 024 flat triangles).
6.2.3 During production, the producing software that generates curved triangles shall determine
automatically the number of curved triangles required to specify the target geometry to the desired
tolerance, knowing that the consuming software will perform five levels of subdivision for any curved
triangle.
6.2.4 To specify curvature, a vertex may contain a child element to specify the desired
surface normal at the vertex. The normal should be unit length and pointing outwards. If this normal is
specified, all triangle edges meeting at that vertex shall be curved so that they are perpendicular to that
normal and in the plane defined by the normal and the original straight edge.
6.2.5 If a vertex is referenced by two volumes, the normal is considered identically for each volume, but
its direction should be interpreted as consistent with the volume in consideration (so that it is pointing
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ISO/ASTM 52915:2016(E)
outwards). Vertices that have an ambiguous normal because they are common to multiple volumes
should not specify a normal.
6.2.6 A curved triangle shall not be more than 25 % out of plane and shall not include inflections.
6.2.7 When the curvature of the volume’s surface at a vertex is undefined (for example, at a cusp,
corner or edge), an element may be used to specify the curvature of a single nonlinear edge
joining two vertices. The curvature is specified using the tangent direction vectors at the beginning and
end of that edge. The element shall take precedence in case of a conflict with the curvature
implied by a element.
6.2.8 Normals should not be specified for vertices referenced only by planar triangles. Edge elements
should not be specified for linear edges in flat triangles.
6.2.9 When interpreting normal and tangents, second degree Hermite interpolation shall be used. See
A.3 for formulae for carrying out this interpolation.
6.3 Restrictions on geometry
All geometry shall comply with the following restrictions.
— Every triangle shall have exactly three different non-co-linear vertices.
— Triangles shall not intersect or overlap except at their common edges or common vertices.
— Volumes shall enclose a closed contiguous space with non-zero volume.
— Volumes shall not overlap.
— Every vertex shall be referenced by at least three triangles.
— Every pair of vertices shall be referenced by exactly zero or two triangles per volume.
-8
— Any two vertices shall not have identical coordinates. The tolerance used to define equality is 10
units.
— The outward direction of triangles that share an edge in the same volume shall be consistent. The
outward direction is defined by the order of vertices.
7 Material specification
7.1 General
7.1.1 Materials are introduced using the optional element. Any number of materials may
be defined using one element for each. Each material is assigned a unique ID. Geometric
volumes may specify a material ID attribute value on the element that references a material.
The material ID “0” is reserved to represent no selected material (void), see Figure 2.
7.1.2 Material characteristics are contained within each element. The child element
is used to specify the red/green/blue/alpha (RGBA) appearance of the material (see Clause 8
on colour). Additional material properties may be specified using the element, such as
the material name for operational purposes or elastic properties for equipment that can control such
properties, see Figure 3. See A.1 for a description of the AMF elements.
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ISO/ASTM 52915:2016(E)
Key
(a) default (flat) triangle patch
(b) triangle curved using vertex normals
(c) triangle curved using edge tangents
(d) subdivision of a curved triangle patch into four curved subpatches
(e) AMF file containing curved geometry
Figure 2 — Types of triangles used in a mesh
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ISO/ASTM 52915:2016(E)
NOTE The figure shows an AMF file containing five materials. Material 3 is a 40/60 % homogeneous mixture
of the first two materials. Material 4 is a vertically graded material and Material 5 has a periodic checkerboard
substructure.
Figure 3 — Homogeneous and composite materials
7.2 Mixed and graded materials and substructures
7.2.1 New materials can be defined as compositions of other materials. The element is
used to specify the proportions of the composition as a constant or a formula dependent of the x, y and z
coordinates. A constant mixing proportion will lead to a homogeneous material. A coordinate dependent
composition can lead to a graded material. More complex coordinate-dependent proportions can lead to
nonlinear material gradients as well as periodic and non-periodic substructure. The proportion formula
can also refer to a texture map using the tex (textureid,x,y,z) function (see A.1).
7.2.2 Any number of materials may be used within a composite.
7.2.3 Any negative material proportion value shall be interpreted as a zero proportion. Material
proportions shall be normalized to a sum of 1.0 to determine actual ratios.
7.3 Porous materials
7.3.1 Reference to materialid “0” (void) may be used to specify porous structures. The proportion
of void shall be either 0 or 1. Any fractional shall be interpreted as 1 (that is, any fractional void shall be
treated as 0 or fully void).
7.3.2 Although the element could theoretically be used to describe the complete
geometry of an object as a single function or texture with reference to void, producers shall not do
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ISO/ASTM 52915:2016(E)
this (see B.2.5 and B.2.6). The intended use of the element with reference to void is to
describe cellular mesostructures.
7.4 Stochastic materials
Reference to the rand(x,y,z) function may be used to specify pseudo-random materials. For example,
a composite material could combine two base materials in random proportions in which the exact
proportion might depend on the coordinates in various ways. The rand(x,y,z) function produces a
random floating point scalar in the range [0,1] that is persistent across function calls (see A.4).
8 Colour specification
8.1 General
8.1.1 Colours may be introduced using the element by specifying the RGBA (transparency)
[2]
values in a specified colour space. By default, the colour space shall be sRGB but alternative profiles
may be specified using the metadata tag in the root element (see A.1). The element
may be a child of the element to associate a colour with a material, the
element to colour an entire object, the element to colour an entire volume, the
element to colour a triangle or the element to associate a colour with a particular vertex
(see Figure 4).
8.1.2 If no colour is specified, the default colour is white.
8.1.3 Object colour overrides material colour specification; a volume colour overrides an object and
material colours; vertex colours override volume, object and material colours; and triangle colouring
overrides vertex, object and material colours.
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NOTE A solid colour may be associated with a material, a volume or a vertex. A vertex may also be associated
with a coordinate in a colour texture file.
Figure 4 — Colour specification
8.2 Colour gradations and texture mapping
8.2.1 A colour may also be specified by referring to a formula that might use a variety of functions,
including a texture map function.
8.2.2 When referring to a formula, the element may specify a colour that depends on
the coordinates such as a colour gradation. Any mathematical expression that combines the functions
described in A.2 may be used. For example, use of the rand function would allow for pseudorandom
colour patterns. The tex function would allow the colour to depend on a texture map or image. To specify
a full-colour graphic, typically three textures would be needed, one for each colour channel. To create a
monochrome graphic, one texture is typically sufficient.
8.2.3 When the vertices of a single triangle have different colours, the interior colour of the triangle
shall be linearly interpolated between those colours, unless a triangle colour has been explicitly specified
(because a triangle colour takes precedence over a vertex colour). If all three vertices of a triangle contain
a mapping to the same texture ID for any channel (r, g, b or a), the colour of this channel of the triangle
shall be extracted from the texture map, overriding the triangle colour.
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ISO/ASTM 52915:2016(E)
8.3 Transparency
The transparency channel determines alpha compositing for combining the specified foreground
colour with a background colour to create the appearance of partial transparency. A value of 0 specifies
zero transparency, that is, only the foreground colour is used. A value of 1 specifies full transparency,
that is, only the background colour is used. Intermediate values shall be linearly interpolated between
the background and foreground colours. Negative values are rounded to 0 and values greater than one
are truncated to 1. The background colour of a triangle shall be the vertex colour, then volume colour,
then object colour, then material colour in decreasing precedence. The background colour of a vertex
shall be the volume colour, then object colour, then material colour in decreasing precedence. The
background colour of a volume shall be the object colour, then material colour in decreasing precedence.
The background colour of an object shall be the material colour.
9 Texture specification
9.1 The element is used to associate a textureid with particular texture data. The texture
map size shall be specified and both two-dimensional (2D) and three-dimensional (3D) textures are
supported. The data shall be represented as a series of grayscale values in the range [0,255]. Each value is
stored in one byte and encoded in Base64. The ordering of pixel data shall be consistent with the texture
map reference coordinate.
9.2 The producer shall ensure that the amount of data matches the specified size of the texture. If the
amount of data is excessive, the consumer shall truncate it. If the amount of data is too low, the consumer
shall append the data with 0 values as needed to meet the specified texture size.
9.3 In order to map a texture onto a triangle, the element may be used to define u, v and
(optionally) w coordinates for each vertex of this triangle. If the texture’s “tiled” property is “true”, any
u,v,w mappings outside of the [0,1] range shall be determined according to the coordinate modulo 1. If the
texture’s tiled property is not “true”, any mappings that fall outside of the [0,1] range shall return zero.
9.4 Textures shall be linearly interpolated for each triangle. A triangle shall include only a single
element. Overlapping textures shall be combined by the producer into a single texture before
being mapped onto a mesh.
10 Constellations
10.1 Multiple objects may be arranged together using the element (see Figure 5).
A constellation may specify the position and orientation of objects to increase packing efficiency and
describe large arrays of identical objects. The element specifies the displacement and
rotation that an existing object shall be transformed to position it in the constellation. The displacement
and rotation shall be defined relative to the original position and orientation of the object when it was
originally defined. Rotation angles shall be specified in degrees and shall first apply rotations about the x
axis, then the y axis and then the z axis.
10.2 A constellation may include another constellation, with multiple levels of hierarchy. However, cyclic
definitions of constellations shall not be used.
10.3 When multiple objects and constellations are defined in a single file, the position and relative
orientation of only the direct children objects and constellations of the element may be optimized
by the consuming software.
10.4 When interpreting orientation,
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