ASTM ISO/ASTM52915-20

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
ISO/ASTM 52915:2016(E)
ISO/ASTM 52915 − 2020(E)
Standard Specification for
Additive Manufacturing File Formatadditive manufacturing
file format (AMF) Version 1.2
This standard is issued under the fixed designation ISO/ASTM 52915; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision.
INTRODUCTION
This International Standard document 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,color, 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 colourcolor with functionally-defined
functionally defined gradations of materials and microstructures, there is a growing need for a standard
interchange file format that can support these features.
The additiveAdditive 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.
1. Scope
1.1 This International Standard document provides the specification for the Additive Manufacturing File Format (AMF), an
interchange format to address the current and future needs of additive manufacturing technology.
1.2 The AMF may be prepared, displayed and transmitted provided the requirements of this specification are met. This document
specifies the requirements for the preparation, display and transmission for the AMF. When prepared in a structured electronic
format, strict adherence to an extensible markup language (XML)(1) schema is required to support supports standards-compliant
interoperability.
1.3 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 A1.
NOTE 1—A W3C XML schema definition (XSD) for the AMF is available from ISO from http://standards.iso.org/iso/52915 and from ASTM from
This International Standard is under the jurisdiction of ASTM Committee F42 on Additive Manufacturing Technologies and is the direct responsibility of Subcommittee
F42.04 on Design, and is also under the jurisdiction of ISO/TC 261. 261, Additive manufacturing, 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.
Current edition approved Oct. 19, 2015May 1, 2020. Published AprilAugust 20202016. Originally published as ASTM F2915-11. Last previous edition ISO/ASTM
52915-13.52915-16.
The boldface numbers in parentheses refer to the Bibliography at the end of this standard.
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
www.astm.org/MEETINGS/images/amf.xsd. An implementation guide for such an XML schema is provided in Annex A1.
1.3 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. document. Suggested future features are listed in Annex A2.
1.4 This International Standard document does not specify any explicit mechanisms for ensuring data integrity, electronic
signatures,signatures and encryptions.
2. Terminology
2.1 Definitions: For the purposes of this document, the following terms and definitions apply.
2.1.1 AMF consumer—software reading (parsing) the Additive Manufacturing File Format (AMF) file for fabrication,
visualization or analysis.
2.1.1.1 Discussion—
AMF files are typically imported by additive manufacturing equipment, as well as viewing, analysis and verification software.
2.1.2 AMF editor—software reading and rewriting the Additive Manufacturing File Format (AMF) file for conversion.
2.1.2.1 Discussion—
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.
2.1.3 AMF producer—software writing (generating) the Additive Manufacturing Format (AMF) file from original geometric data.
2.1.3.1 Discussion—
AMF files are typically exported by computer-aided design (CAD) software, scanning software, or directly from computational
geometry algorithms.
2.1.4 attribute—characteristic of data, representing one or more aspects or descriptors of the data in an element.
2.1.4.1 Discussion—
In the XML framework, attributes are characteristics of elements.
2.1.5 comments—all text comments associated with any data within the Additive Manufacturing File Format (AMF) to be ignored
by import software.
2.1.5.1 Discussion—
Comments are used for enhancing human readability of the file and for debugging purposes.
2.1.6 element—information unit within an XML document consisting of a start tag, an end tag, the content between the tags, and
any attributes.
2.1.6.1 Discussion—
In the XML framework, an element can contain data, attributes and other elements.
2.1.7 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.
2.1.7.1 Discussion—
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). ISO/ASTM 52900-2015
2.1.8 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.
2.1.8.1 Discussion—
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. ISO/ASTM 52900-2015
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
2. Normative references
2.1 There are no normative references in this document.
3. Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
– ISO Online browsing platform: available at http://www.iso.org/obp
– IEC Electropedia: available at http://www.electropedia.org/
3.1 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.
3.2 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.
3.3 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.
3.4 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.
3.5 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.
3.6 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.
3.7 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]
3.8 STL
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]
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
4. Key considerations
4.1 General:General
4.1.1 There is a natural tradeofftrade-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, document, the AMF, is designed
to address the concerns listed in 3.1.24.1.2 to 3.1.74.1.7.
4.1.2 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 only certain advanced machines
support (for example, colour,color, multiple materials), but these are defined in such a way as to avoid exclusivity.
4.1.3 Simplicity—The AMF format 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.
4.1.4 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.
4.1.5 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 A2.
4.1.6 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.
4.1.7 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.
4.2 Guidelines for the inclusion of future new elements:
4.2.1 Any new element proposed shall be applicable across all hardware platforms and technologies that could conceivably be
used to generate the desired outcome.
4.2.2 In support of the consideration above, new elements proposed for this International Standard document 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
LayerFillPath> that describes how to build a hollow volume shall not be included since
it assumes a particular fabrication process.
5. Structure of this specification
5.1 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.
5.2 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.
5.3 Precision—This file format is agnostic as to the precision of the representation of numeric values. It is the responsibility of
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
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).
5.4 Future amendments and additions—While additional XML elements can be added provisionally to any AMF file for internal
purpose, such additions will 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.
6. General structure
6.1 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.
6.2 Whitespace characters and standard XML comments may be interspersed in the file and shall be ignored by any interpreter,
for example:

6.3 The remainder of the file shall be enclosed between start and end element tags. This element denotes the
file type and fulfills 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 absence of a unit specification, the attribute value millimetres is assumed.assumed, for example:
xmins:amf=”www.astm.org/Standards/F2915–14”>
xmins : amf=”www.astm.org/Standards/F2915–14”>
6.4 Enclosed within the element start- and end-tags, there are five top level elements, as described in 5.4.16.4.1 to
5.4.56.4.5.
6.4.1 —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.
6.4.2 —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.
6.4.3 —The optional texture element defines one image or texture for colourcolor or texture mapping, each of which
declares an associated texture ID. The texture ID thus declared shall be unique.
6.4.4 —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.
6.4.5 —The optional metadata element specifies additional information about the object(s) and elements contained
in the file.
6.5 Only a single object element is required for a fully functional AMF file.
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
7. Geometry specification
7.1 General:
7.1.1 The top level element declares a unique ID and shall contain once child element. The element
shall contain two child elements: and . The element may optionally reference a material.
7.1.2 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.
7.1.3 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.
7.1.4 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 Fig. 1).
7.1.5 The geometry shall not be used to describe support structure. Only the final target structure shall be described.
7.2 Smooth geometry:
NOTE 1—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.
FIG. 1 Basic AMF file
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
7.2.1 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 Section 13) may ignore curvature information
associated with triangles.
7.2.2 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 1024 flat
triangles).
7.2.3 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.
7.2.4 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.
7.2.5 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 outwards). Vertices that have an ambiguous normal
because they are common to multiple volumes should not specify a normal.
7.2.6 A curved triangle shall not be more than 25 % out of plane and shall not include inflections.
7.2.7 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.
7.2.8 Normals should not be specified for vertices referenced only by planar triangles. Edge elements should not be specified for
linear edges in flat triangles.
7.2.9 When interpreting normal and tangents, second degree Hermite interpolation shall be used. See A1.3 for formulae for
carrying out this interpolation.
7.3 Restrictions on geometry—All geometry shall comply with the following restrictions:
7.3.1 Every triangle shall have exactly three different non-colinear vertices.
7.3.2 Triangles shall not intersect or overlap except at their common edges or common vertices.
7.3.3 Volumes shall enclose a closed contiguous space with non-zero volume.
7.3.4 Volumes shall not overlap.
7.3.5 Every vertex shall be referenced by at least three triangles.
7.3.6 Every pair of vertices shall be referenced by exactly zero or two triangles per volume.
-8
7.3.7 Any two vertices shall not have identical coordinates. The tolerance used to define equality is 10 units.
7.3.8 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.
8. Material specification
8.1 General:
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
8.1.1 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 Fig. 2.
8.1.2 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 Section 89 on colour).color). 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 Fig. 3. See Annex A1 for a description of the AMF elements.
8.2 Mixed and graded materials and substructures:
8.2.1 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 Annex A1).
8.2.2 Any number of materials may be used within a composite.
8.2.3 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.
8.3 Porous materials:
8.3.1 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).
8.3.2 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 this (see A2.2.5 and A2.2.6). The intended use of the
element with reference to void is to describe cellular mesostructures.
8.4 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. Therand(x,y,z) function produces a random floating point scalar in the range [0,1]
that is persistent across function calls (see A1.4).
9. colourColor specification
9.1 General:
9.1.1 coloursColors may be introduced using the element by specifying the RGBA (transparency) values
in a specified colourcolor space. By default, the colourcolor space shall be sRGB (2) but alternative profiles may be specified using
the metadata tag in the root element (see Annex A1). The element may be a child of the
element to associate a colourcolor with a material, the element to colourcolor an entire object, the
element to colourcolor an entire volume, the element to colourcolor a triangle, or the
element to associate a colourcolor with a particular vertex (see Fig. 4).
9.1.2 If no colourcolor is specified, the default colourcolor is white.
9.1.3 Object colourcolor overrides material colourcolor specification; a volume colourcolor overrides an object and material
colours;colors; vertex colourscolors override volume, object, and material colours;colors; and triangle colouringcoloring overrides
vertex, object, and material colours.colors.
9.2 colourCoulor gradations and texture mapping:
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
FIG. 2 Types of triangles used in a mesh
9.2.1 A colourcolor may also be specified by referring to a formula that might use a variety of functions, including a texture map
function.
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
NOTE 1—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.
FIG. 3 Homogeneous and composite materials
9.2.2 When referring to a formula, the element may specify a colourcolor that depends on the coordinates
such as a colourcolor gradation. Any mathematical expression that combines the functions described in A1.2 may be used. For
example, use of the rand function would allow for pseudo-random colourcolor patterns. The tex function would allow the
colourcolor to depend on a texture map or image. To specify a full-colourfull-color graphic, typically three textures would be
needed, one for each colourcolor channel. To create a monochrome graphic, one texture is typically sufficient.
9.2.3 When the vertices of a single triangle have different colours,colors, the interior colourcolor of the triangle shall be linearly
interpolated between those colours,colors, unless a triangle colourcolor has been explicitly specified (because a triangle colourcolor
takes precedence over a vertex colour).color). If all three vertices of a triangle contain a mapping to the same texture ID for any
channel (r,g,b or a), the colourcolor of this channel of the triangle shall be extracted from the texture map, overriding the triangle
colour.color.
9.3 Transparency—The transparency channel determines alpha compositing for combining the specified foreground
colourcolor with a background colourcolor to create the appearance of partial transparency. A value of 0 specifies zero
transparency, that is, only the foreground colourcolor is used. A value of 1 specifies full transparency, that is, only the background
colourcolor is used. Intermediate values shall be linearly interpolated between the background and foreground colours.colors.
Negative values are rounded to 0 and values greater than one are truncated to 1. The background colourcolor of a triangle shall
be the vertex colour,color, then volume colour,color, then object colour,color, then material colourcolor in decreasing precedence.
The background colourcolor of a vertex shall be the volume colour,color, then object colour,color, then material colourcolor in
decreasing precedence. The background colourcolor of a volume shall be the object colour,color, then material colourcolor in
decreasing precedence. The background colourcolor of an object shall be the material colour.color.
10. Texture specification
10.1 The element is used to associate atextureID ortextureid 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
© ISO/ASTM International 2020 – All rights reserved
ISO/ASTM 52915:2020(E)
NOTE 1—A solid colourcolor may be associated with a material, a volume or a vertex. A vertex may also be associated with a coordinate in a colourcolor
texture file.
FIG. 4 ColourColor specification
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.
10.2 The producer shall ensure that the amo
...