2.4. DREAM3D File Specification

“/” Root Object

Required Attributes

Name	Type	Value
FileVersion	Null Term String	“8.0”

HDF5 Groups

Name	Type	Notes
DataStructure	HDF5 Group	Name will not change
Pipeline	HDF5 Group	Name will not change

General Notes on the ‘Pipeline’ HDF5 Group

This holds a single null term STRING data set that holds the JSON formatted pipeline that was used to create the file. If you are trying to write a compatible .dream3d file this can be omitted.

General Notes on the ‘DataStructure’ HDF5 Group

• The name will not change

• Each object within the ‘DataStructure’ group, including the ‘DataStructure’ group itself has a unique id associated with it.

  • Name: NextObjectId

  • Type: 64 Bit Unsigned Integer

  • Value: unique value

• Each HDF5 object within the ‘DataStructure’ HDF5 group represents either a Group, Geometry, AttributeMatrix or DataArray.

DataObject Attributes

These attributes are on every DataObject:

Name	Type	Notes
Importable	Scalar UINT64	Only important if you are going to be writing a compatible .dream3d file
ObjectId	Scalar UINT64	Only important if you are going to be writing a compatible .dream3d file
ObjectType	Null Term String	Describes the class of the object

ObjectType Possible Values:

• DynamicListArray

• ScalarData

• BaseGroup +

• AttributeMatrix

• DataGroup

• IDataArray +

• DataArray

• IGeometry +

• IGridGeometry +

• RectGridGeom

• ImageGeom

• INodeGeometry0D +

• VertexGeom

• INodeGeometry1D +

• EdgeGeom

• INodeGeometry2D +

• QuadGeom

• TriangleGeom

• INodeGeometry3D +

• HexahedralGeom

• TetrahedralGeom

• INeighborList +

• NeighborList

• StringArray

• AbstractMontage +

• GridMontage

+: These theoretically should never show up as they are abstract classes.

Specific ObjectType Attributes

Based on the ObjectType, there can be additional attriutes that can be read based on the ObjectType value

AttributeMatrix

Name	Type	Notes
TupleDims	N x UINT64	Dimensions of the contained arrays from fastest to slowest. Note that for data arrays that are in the “Cell Data” inside an ImageGeometry or RectGrid Geometry, the dimensions will be in reverse order from the _DIMENSIONS attribute on the geometry in question.

DataArray<XXXXX>

The value of the ObjectType HDF5 attribute will have the numeric type encoded in the name. For example if the DataArray represents 32 bit floating point values, then the actual string will show up as DataArray<float32>. Here are the possibilities:

• DataArray<uint8>

• DataArray<int8>

• DataArray<uint16>

• DataArray<int16>

• DataArray<uint32>

• DataArray<int32>

• DataArray<uint64>

• DataArray<int64>

• DataArray<float32>

• DataArray<float64>

Name	Type	Notes
ComponentDimensions	N x UINT64	Dimensions of the components of the array.
TupleDimensions	N x UINT64	Dimensions of the contained arrays from fastest to slowest. Note that for data arrays that are in the “Cell Data” inside an ImageGeometry or RectGrid Geometry, the dimensions will be in reverse order from the _DIMENSIONS attribute on the geometry in question.

ImageGeometry

Name	Type	Notes
_DIMENSIONS	3 x UINT64	Regular Grid Dimensions as XYZ
_ORIGIN	3 x Float32	Origin as XYZ
_SPACING	3 x Float32	Spacing of each axis as XYZ
Cell Data ID	Scalar UINT64	Unique ObjectId of the Cell Data AttributeMatrix

Vertex Geometry

The HDF5 Group contains the following required attributes:

Name	Type	Notes
ObjectType	STRING	VertexGeom
Vertex List ID	UINT64	ObjectId of the SharedVertexList data array.
Vertex Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the vertex

The Vertex Geometry HDF5 Group should contain at the minimum 2 Data Arrays:

Name	Type	Notes
SharedVertexList	3 x Float32	Each set represents the XYZ coordinate of a vertex

Edge Geometry

The HDF5 Group contains the following required attributes:

Name	Type	Notes
ObjectType	STRING	EdgeGeom
Vertex List ID	UINT64	ObjectId of the SharedVertexList data array.
Vertex Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the vertex
Edge List ID	UINT64	ObjectId of the SharedEdgeList data array
Edge Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the edges

The Edge Geometry HDF5 Group should contain at the minimum 2 Data Arrays that represent the vertices (Nodes) and faces (Elements) of the Edge Geometry. Shown below are the default names that are used. The arrays can be named differently by the user.

Name	Type	Notes
SharedVertexList	3 x Float32	Each set represents the XYZ coordinate of a vertex
SharedEdgeList	2 x UINT64	Each set represents the 2 vertices of the Edge where each value is an index into the SharedVertexList

Triangle Geometry

The HDF5 Group contains the following required attributes:

Name	Type	Notes
ObjectType	STRING	TriangleGeom
Vertex List ID	UINT64	ObjectId of the SharedVertexList data array.
Vertex Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the vertex
Face List ID	UINT64	ObjectId of the SharedTriangleList data array
Face Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the triangle faces

The Triangle Geometry HDF5 Group should contain at the minimum 2 Data Arrays that represent the vertices (Nodes) and faces (Elements) of the Triangle Geometry. Shown below are the default names that are used. The arrays can be named differently by the user.

Name	Type	Notes
SharedVertexList	3 x Float32	Each set represents the XYZ coordinate of a vertex
SharedFaceList	3 x UINT64	Each set represents the 3 vertices of the triangle where each value is an index into the SharedVertexList

Quad Geometry

The HDF5 Group contains the following required attributes:

Name	Type	Notes
ObjectType	STRING	QuadGeom
Vertex List ID	UINT64	ObjectId of the SharedVertexList data array.
Vertex Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the vertex
Face List ID	UINT64	ObjectId of the SharedFaces data array
Face Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the Quad faces

The Quad Geometry HDF5 Group should contain at the minimum 2 Data Arrays that represent the vertices (Nodes) and faces (Elements) of the Quad Geometry. Shown below are the default names that are used. The arrays can be named differently by the user.

Name	Type	Notes
SharedVertexList	3 x Float32	Each set represents the XYZ coordinate of a vertex
SharedFaceList	4 x UINT64	Each set represents the 4 vertices of the triangle where each value is an index into the SharedVertexList

Tetrahedral Geometry

The HDF5 Group contains the following required attributes:

Name	Type	Notes
ObjectType	STRING	QuadGeom
Vertex List ID	UINT64	ObjectId of the SharedVertexList data array.
Vertex Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the vertex
Cell List ID	UINT64	ObjectId of the SharedCell data array
Cell Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the Tetrahedral cells

The Tetrahedral Geometry HDF5 Group should contain at the minimum 2 Data Arrays that represent the vertices (Nodes) and cells (Elements) of the Tetrahedral Geometry. Shown below are the default names that are used. The arrays can be named differently by the user.

Name	Type	Notes
SharedVertexList	3 x Float32	Each set represents the XYZ coordinate of a vertex
SharedCellList	4 x UINT64	Each set represents the 4 vertices of the triangle where each value is an index into the SharedVertexList

Hexahedral Geometry

The HDF5 Group contains the following required attributes:

Name	Type	Notes
ObjectType	STRING	QuadGeom
Vertex List ID	UINT64	ObjectId of the SharedVertexList data array.
Vertex Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the vertex
Cell List ID	UINT64	ObjectId of the SharedCell data array
Cell Data ID	UINT64	ObjectId of the Attribute Matrix that holds data arrays geometrically located at the Hexahedral cells

The Hexahedral Geometry HDF5 Group should contain at the minimum 2 Data Arrays that represent the vertices (Nodes) and cells (Elements) of the Hexahedral Geometry. Shown below are the default names that are used. The arrays can be named differently by the user.

Name	Type	Notes
SharedVertexList	3 x Float32	Each set represents the XYZ coordinate of a vertex
SharedCellList	8 x UINT64	Each set represents the 8 vertices of the triangle where each value is an index into the SharedVertexList