2.3.3.3.7. Geometry & Microstructure

Base Classes

The following base classes are defined to incentivize the use of NeXus for using computational-geometry-based descriptions. In what follows, base classes for frequently used shapes and geometric primitives are proposed:

NXcg_primitive:

Base class from which most other NXcg classes that define specific primitives inherit.

NXcg_ellipsoid:

A description for a set of possibly dissimilar oriented ellipsoids.

NXcg_cylinder:

A description for a set of possibly dissimilar oriented cylinders.

NXcg_point:

A collection of points with labels.

NXcg_polyline:

A collection of lines and linear segments.

NXcg_triangle:

A collection of triangles.

NXcg_parallelogram:

A collection of possibly dissimilar parallelograms.

NXcg_polygon:

A collection of polygons.

NXcg_tetrahedron:

A collection of tetrahedra.

NXcg_hexahedron:

A collection of hexahedra with capabilities to represent also simpler (bounding) boxes for e.g. binary trees.

NXcg_polyhedron:

A collection of polyhedra.

NXcg_roi:

A container to host a number of different types of primitives.

These base classes describe data structures used for more complex geometries:

NXcg_face_list_data_structure:

In essence, the usual way how polygon/polyhedra data are reported: A list of vertices and faces with identifier and properties.

NXcg_half_edge_data_structure:

A half-edge data structure (also known as a doubly connected edge list) is a useful complementary descriptor for polygon/polyhedra which enables topological analyses and traversal of the graph of how polygons and polyhedra are connected.

NXcg_unit_normal:

As an additional structuring element especially for meshes, well-documented normal information is crucial for distance computations.

NXcg_alpha_complex:

Alpha shapes and alpha wrappings, specifically the special case of the convex hull, are frequently used geometrical models for describing a boundary or edge to a set of geometric primitives.

Next, a few base classes are defined for documenting discretized representations of material (area or volume) which can be useful not only for stencil-based methods:

NXcg_grid:

A grid of cells.

NXisocontour:

A description for isocontour descriptions.

NXdelocalization:

An approach to document procedures whereby a scalar field is smoothed in a controlled manner.

NXsimilarity_grouping:

A description for clustering of objects (such as atoms or features).

TODO CHECK THAT MICROSTRUCTURE PART IS COVERED IN ICME WHEN MICROSTRUCTURE PROPOSAL SYNCED UP