DREAM3D User Manual
DREAM.3D Data Structure

DREAM3D uses a data structure that is based on the concepts of combinatorial topology and common methods for describing mesh structures. Any topological network (in 2- or 3-D) can be decribed with a the following hierarchy:

DataStructure-2.png
DREAM3D Data Structure

If the mesh (or network) is 2-D, then the Volume element does not exist and the Face element is the highest level element. For typical voxel-based data, the voxels are the Volume elements and within DREAM.3D are referred to as Cells. Similarly, in a surface mesh with triangular patches, the triangles are the Face elements and within DREAM.3D are referred to as Faces. This topology is required to describe the "mesh" or "structure" of the data itself and is not/cannot be adjusted/defined by the user.

However, once the topology of the "structure" is set, the user can begin grouping topological elements into higher level features of the "structure". Below is an example of this grouping for a voxel-based dataset of a polycrystalline metal.

DataStructure-1.png
DREAM.3D Data Structure

DREAM.3D uses two additional levels above the topological levels required to define the "structure" of the data. These two levels are called: Field and Ensemble. These levels allow the user to group topological elements together based on criteria of similarity. For the example above, the Cells are grouped to identify Fields (i.e. grains) by applying a criterion of similar crystallographic orientation (i.e. neighboring Cells with similar orientation are said to belong to the same Field). The Fields are then grouped to identify Ensembles by a criterion of similar phase (i.e. all grains of the same phase in the dataset are said to belong to the same Ensemble). The grouping criteria are at the discretion of the user, because these additional levels are not required for description of the "structure", but rather are organizational levels for describing the information that lives on the "structure".

At each level, DREAM.3D creates a Map to store information/data about the individual elements at that level. Additional information about the maps of the DREAM.3D data structure and "typical" data are given below:

Vertex

  • Map of attributes associated with single points.
  • Measured values (i.e. Orientation, Chemistry, Greyscale, etc.) - generally measured data is not represented at the Vertex level, but the user could choose to store measured values at the Vertices rather than the more typical Cell-centered convention.
  • Calculated values (i.e. Curvatures, Coordination, etc.) - these calculated values are typically values associated with the connectivity or geometry of the "mesh" or "structure" itself.

Edge

  • Map of attributes associated with edges of Faces.
  • Measured values - data is not typically measured at the Edge level.
  • Calculated values (i.e. Curvatures, Coordination, etc.) - these calculated values are typically values associated with the connectivity or geometry of the "mesh" or "structure" itself.

Face

  • Map of attributes associated with surface patches.
  • Measured values - data is not typically measured at the Face level.
  • Calculated values (i.e. Bounding Field Ids, Normals, Curvature, etc.) - these calculated values are typically IDs to the higher level maps (Field and Ensemble), related to gradients of the measured values, values associated with the connectivity or geometry of the "mesh" or "structure" itself or relationships to values calculated in the higher level maps.

Cell

  • Map of attributes associated with single datapoints - often these datapoints are not truly volumes, but rather point-probe measurements that are homogenized over the volume nearest to each probe-point.
  • Measured values (i.e. Orientation, Chemistry, Greyscale, etc.) - typically this is the level at which most data is actually acquired.
  • Calculated values (i.e. Field Ids, Kernel Avg. Misorientation, Euclidean Distance, etc.) - these calculated values are typically IDs to the higher level maps (Field and Ensemble), related to gradients of the measured values or relationships to values calculated in the higher level maps.

Field

  • Map of attributes associated with sets of datapoints - generally elements in this map are sets of contiguous Cells that have some aspect of similarity, often in their measured values (i.e. orientation, chemistry, greyscale, etc.).
  • Measured values (i.e. Avg. Stresses, Avg. Strains, etc) - some measurement techniques are capable of measuring values averaged over an entire Field (i.e. High Energy Diffraction Microscopy).
  • Calculated values (i.e. Avg. Orientation, Size, Shape, No. of Neighbors, etc.) - generally there is little measured data at this level and these values are calculated from averaging the measured data from the Cells that constitute each Field or geometrically describe the size and/or shape of the set of Cells.

Ensemble

  • Map of attributes associated with sets of Fields
  • Measured/Set values (i.e. Crystal Structure, Phase Type, etc.) - measured values at the Ensemble level are usually user-defined parameters during the data collection or during analysis within DREAM.3D.
  • Calculated values (i.e. Size Distribution, No. of Fields, ODF, etc.) - these values are typically descriptions of the distribution of values from the lower level Field map.
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