Mesh Blueprint

The Mesh Blueprint is a set of hierarchical conventions to describe mesh-based simulation data both in-memory and via files. This section provides details about the Mesh Blueprint. Lots of them.

These docs provide the main reference for all of the components of the Mesh Blueprint protocol and details about Mesh Blueprint Examples that are included in the Conduit Blueprint Library.

Conduit docs don’t have a Mesh Blueprint tutorial yet, if you are looking to wrap your mind around the basic mechanics of describing a mesh:

Protocol

The Blueprint protocol defines a single-domain computational mesh using one or more Coordinate Sets (via child coordsets), one or more Topologies (via child topologies), zero or more Materials Sets (via child matsets), zero or more Fields (via child fields), optional Adjacency Set information (via child adjsets), and optional State information (via child state). The protocol defines multi-domain meshes as Objects that contain one or more single-domain mesh entries. For simplicity, the descriptions below are structured relative to a single-domain mesh Object that contains one Coordinate Set named coords, one Topology named topo, and one Material Set named matset.

Coordinate Sets

To define a computational mesh, the first required entry is a set of spatial coordinate tuples that can underpin a mesh topology.

The mesh blueprint protocol supports sets of spatial coordinates from three coordinate systems:

  • Cartesian: {x,y,z}
  • Cylindrical: {r,z}
  • Spherical: {r,theta,phi}

The mesh blueprint protocol supports three types of Coordinate Sets: uniform, rectilinear, and explicit. To conform to the protocol, each entry under coordsets must be an Object with entries from one of the cases outlined below:

  • uniform

    An implicit coordinate set defined as the cartesian product of i,j,k dimensions starting at an origin (ex: {x,y,z}) using a given spacing (ex: {dx,dy,dz}).

    • Cartesian
      • coordsets/coords/type: “uniform”
      • coordsets/coords/dims/{i,j,k}
      • coordsets/coords/origin/{x,y,z} (optional, default = {0.0, 0.0, 0.0})
      • coordsets/coords/spacing/{dx,dy,dz} (optional, default = {1.0, 1.0, 1.0})
    • Cylindrical
      • coordsets/coords/type: “uniform”
      • coordsets/coords/dims/{i,j}
      • coordsets/coords/origin/{r,z} (optional, default = {0.0, 0.0})
      • coordsets/coords/spacing/{dr,dz} (optional, default = {1.0, 1.0})
    • Spherical
      • coordsets/coords/type: “uniform”
      • coordsets/coords/dims/{i,j}
      • coordsets/coords/origin/{r,theta,phi} (optional, default = {0.0, 0.0, 0.0})
      • coordsets/coords/spacing/{dr,dtheta, dphi} (optional, default = {1.0, 1.0, 1.0})
  • rectilinear

    An implicit coordinate set defined as the cartesian product of passed coordinate arrays.

    • Cartesian
      • coordsets/coords/type: “rectilinear”
      • coordsets/coords/values/{x,y,z}
    • Cylindrical:
      • coordsets/coords/type: “rectilinear”
      • coordsets/coords/values/{r,z}
    • Spherical
      • coordsets/coords/type: “rectilinear”
      • coordsets/coords/values/{r,theta,phi}
  • explicit

    An explicit set of coordinates, which includes values that conforms to the mcarray blueprint protocol.

    • Cartesian
      • coordsets/coords/type: “explicit”
      • coordsets/coords/values/{x,y,z}
    • Cylindrical
      • coordsets/coords/type: “explicit”
      • coordsets/coords/values/{r,z}
    • Spherical
      • coordsets/coords/type: “explicit”
      • coordsets/coords/values/{r,theta,phi}

Note

In all of the coordinate space definitions outlined above, spherical coordinates adhere to the definitions of theta/phi used in the physics and engineering domains. Specifically, this means that theta refers to the polar angle of the coordinate (i.e. the angle from the +Z cartesian axis) and phi refers to the azimuthal angle of the coordinate (i.e. the angle from the +X cartesian axis). The figure below most succinctly describes these conventions:

_images/spherical_coordinates_render.png

Figure of spherical coordinate conventions (courtesy of Wikipedia)

Toplogies

The next entry required to describe a computational mesh is its topology. To conform to the protocol, each entry under topologies must be an Object that contains one of the topology descriptions outlined below.

Topology Nomenclature

The mesh blueprint protocol describes meshes in terms of vertices, edges, faces, and elements.

The following element shape names are supported:

Name Geometric Type Specified By
point point an index to a single coordinate tuple
line line indices to 2 coordinate tuples
tri triangle indices to 3 coordinate tuples
quad quadrilateral indices to 4 coordinate tuples
tet tetrahedron indices to 4 coordinate tuples
hex hexahedron indices to 8 coordinate tuples
polygonal polygon indices to N end-to-end coordinate tuples
polyhedral polyhedron indices to M polygonal faces

Association with a Coordinate Set

Each topology entry must have a child coordset with a string that references a valid coordinate set by name.

  • topologies/topo/coordset: “coords”

Optional association with a Grid Function

Topologies can optionally include a child grid_function with a string that references a valid field by name.

  • topologies/topo/grid_function: “gf”

Implicit Topology

The mesh blueprint protocol accepts four implicit ways to define a topology on a coordinate set. The first simply uses all the points in a given coordinate set and the rest define grids of elements on top of a coordinate set. For the grid cases with a coordinate set with 1D coordinate tuples, line elements are used, for sets with 2D coordinate tuples quad elements are used, and for 3D coordinate tuples hex elements are used.

  • points: An implicit topology using all of the points in a coordinate set.

    • topologies/topo/coordset: “coords”
    • topologies/topo/type: “points”
  • uniform: An implicit topology that defines a grid of elements on top of a uniform coordinate set.

    • topologies/topo/coordset: “coords”
    • topologies/topo/type: “uniform”
    • topologies/topo/elements/origin/{i,j,k} (optional, default = {0,0,0})
  • rectilinear: An implicit topology that defines a grid of elements on top of a rectilinear coordinate set.

    • topologies/topo/coordset: “coords”
    • topologies/topo/type: “rectilinear”
    • topologies/topo/elements/origin/{i,j,k} (optional, default = {0,0,0})
  • structured: An implicit topology that defines a grid of elements on top of an explicit coordinate set.
    • topologies/topo/coordset: “coords”
    • topologies/topo/type = “structured”
    • topologies/topo/elements/dims/{i,j,k}
    • topologies/topo/elements/origin/{i0,j0,k0} (optional, default = {0,0,0})

Explicit (Unstructured) Topology

Single Shape Topologies

For topologies using a homogenous collection of element shapes (eg: all hexs), the topology can be specified by a connectivity array and a shape name.

  • topologies/topo/coordset: “coords”
  • topologies/topo/type: “unstructured”
  • topologies/topo/elements/shape: (shape name)
  • topologies/topo/elements/connectivity: (index array)
Mixed Shape Toplogies

For topologies using a non-homogenous collections of element shapes (eg: hexs and tets), the topology can specified using a single shape topology for each element shape.

  • list - A Node in the List role, that contains a children that conform to the Single Shape Topology case.
  • object - A Node in the Object role, that contains a children that conform to the Single Shape Topology case.

Note

Future version of the mesh blueprint will expand support to include mixed elements types in a single array with related index arrays.

Element Windings

The mesh blueprint does yet not have a prescribed winding convention (a way to order the association of vertices to elements) or more generally to outline a topology’s dimensional cascade (how elements are related to faces, faces are related to edges, and edges are related to vertices. )

This is a gap we are working to solve in future versions of the mesh blueprint, with a goal of providing transforms to help convert between different winding or cascade schemes.

That said VTK (and VTK-m) winding conventions are assumed by MFEM, VisIt, or Ascent when using Blueprint data.

Polygonal/Polyhedral Topologies

The polygonal and polyhedral topology shape types are structurally identical to the other explicit topology shape types (see the Single Shape Topologies section above), but the contents of their elements sections look slightly different. In particular, these sections are structured as o2mrelation objects that map elements (the ones) to their subelement constituents (the many). For polyhedral topologies, these constituents reside in an additional subelements section that specifies the polyhedral faces in a format identical to elements in a polygonal schema.

Polygonal Topologies

The schema for a polygonal shape topology is as follows:

  • topologies/topo/coordset: “coords”
  • topologies/topo/type: “unstructured”
  • topologies/topo/elements: (o2mrelation object)
  • topologies/topo/elements/shape: “polygonal”
  • topologies/topo/elements/connectivity: (index array)

It’s important to note that the elements/connectivity path defines the vertex index sequences (relative to coordset) for each element in the topology. These vertex sequences must be arranged end-to-end (i.e. such that (v[i], v[i+1]) defines an edge) relative to their container polygonal elements.

The following diagram illustrates a simple polygonal topology:

#
#    4--------5
#    |`--     |
# e1 |   `.   | e0
#    |     --.|
#    7--------6
#

topologies:
  topology:
    coordset: coords
    type: unstructured
    elements:
      shape: polygonal
      connectivity: [4, 6, 5, 7, 6, 4]
      sizes: [3, 3]
      offsets: [0, 3]
Polyhedral Topologies

The schema for a polyhedral shape topology is as follows:

  • topologies/topo/coordset: “coords”
  • topologies/topo/type: “unstructured”
  • topologies/topo/elements: (o2mrelation object)
  • topologies/topo/elements/shape: “polyhedral”
  • topologies/topo/elements/connectivity: (index array)
  • topologies/topo/subelements: (o2mrelation object)
  • topologies/topo/subelements/shape: (shape name)
  • topologies/topo/subelements/connectivity: (index array)

An important nuance to the structure of a polyhedral shape topology is that the elements/connectivity path indexes into the subelements object to list the many faces associated with each one polyhedron. Similarly, the subelements/connectivity path indexes into the coordset path to list the many vertices associated with each one polyhedral face. There is no assumed ordering for constituent polyhedral faces relative to their source polyhedra.

The following diagram illustrates a simple polyhedral topology:

#
#         0
#        /|\
#       / | \ <- e0
#      /  |  \
#     /_.-3-._\
#    1.,  |  ,.4
#     \ `'2'` /
#      \  |  /
# e1 -> \ | /
#        \|/
#         5
#|

topologies:
  topology:
    coordset: coords
    type: unstructured
    elements:
      shape: polyhedral
      connectivity: [0, 1, 2, 3, 4, 0, 5, 6, 7, 8]
      sizes: [5, 5]
      offsets: [0, 5]
    subelements:
      shape: polygonal
      connectivity: [1, 2, 4, 3, 1, 2, 0, 2, 4, 0, 4, 3, 0, 3, 1, 0, 1, 2, 5, 2, 4, 5, 4, 3, 5, 3, 1, 5]
      sizes: [4, 3, 3, 3, 3, 3, 3, 3, 3]
      offsets: [0, 4, 7, 10, 13, 16, 19, 22, 25]

Material Sets

Materials Sets contain material name and volume fraction information defined over a specified mesh topology.

A material set is a type of o2mrelation that houses per-material, per-element volume fractions that are defined over a referenced source topology. Each material set conforms to a schema variant based on:

  • The layout of its per-material buffers.
  • The indexing scheme used to associate volume fractions with topological elements.

The options for each of these variants are detailed in the following sections.

Material Set Buffer Variants

Each material set follows one of two variants based on the presented structure of its volume fractions. These variants cover volume fractions presented in a single, unified buffer (called uni-buffer presentation) and in multiple, per-material buffers (called multi-buffer presentation). Both of these variants and their corresponding schemas are outlined in the subsections below.

Uni-Buffer Material Sets

A uni-buffer material set is one that presents all of its volume fraction data in a single data buffer. In this case, the material set schema must include this volume fraction data buffer, a parallel buffer associating each volume with a material identifier, and an Object that maps human-readable material names to unique integer material identifiers. Additionally, the top-level of this schema is an o2mrelation that sources from the volume fraction/material identifier buffers and targets the material topology. To conform to protocol, each matsets child of this type must be an Object that contains the following information:

  • matsets/matset/topology: “topo”
  • matsets/matset/material_map: (object with integer leaves)
  • matsets/matset/material_ids: (integer array)
  • matsets/matset/volume_fractions: (floating-point array)

The following diagram illustrates a simple uni-buffer material set example:

#     z0       z1       z2
# +--------+--------+--------+
# | a0     | a1 ___/|        |
# |___-----|----    |   b2   |
# |     b0 |     b1 |        |
# +--------+--------+--------+
#

matsets:
  matset:
    topology: topology
    material_map:
      a: 1
      b: 2
      c: 0
    material_ids: [0, 1, 2, 2, 2, 0, 1, 0]
    volume_fractions: [0, a0, b2, b1, b0, 0, a1, 0]
    sizes: [2, 2, 1]
    offsets: [0, 2, 4]
    indices: [1, 4, 6, 3, 2]
Multi-Buffer Material Sets

A multi-buffer material set is a material set variant wherein the volume fraction data is split such that one buffer exists per material. The schema for this variant dictates that each material be presented as an Object entry of the volume_fractions field with the material name as the entry key and the material volume fractions as the entry value. Multi-buffer material sets also support an optional material_map, which is an Object that maps human-readable material names to unique integer material identifiers. If omitted, the map from material names to ids is inferred from the order of the material names in the volume_fractions node.

Optionally, the value for each such entry can be specified as an o2mrelation instead of a flat array to enable greater specification flexibility. To conform to protocol, each matsets child of this type must be an Object that contains the following information:

  • matsets/matset/topology: “topo”
  • matsets/matset/volume_fractions: (object)
  • matsets/matset/material_map: (optional, object with integer leaves)

The following diagram illustrates a simple multi-buffer material set example:

#     z0       z1       z2
# +--------+--------+--------+
# | a0     | a1 ___/|        |
# |___-----|----    |   b2   |
# |     b0 |     b1 |        |
# +--------+--------+--------+
#

matsets:
  matset:
    topology: topology
    volume_fractions:
      a:
        values: [0, 0, 0, a1, 0, a0]
        indices: [5, 3]
      b:
        values: [0, b0, b2, b1, 0]
        indices: [1, 3, 2]
    material_map: # (optional)
      a: 0
      b: 1

Material Set Indexing Variants

Material sets can also vary in how volume fractions are associated with topological elements. This associative variance leads to two additional schema variants: element-dominant (elements/volumes have the same ordering) and material-dominant (elements/volumes have independent orderings). Both of these variants and their corresponding schemas are outlined in the subsections below.

Element-Dominant Material Sets

In an element-dominant material set, the volume fraction data order matches the topological element order. In other words, the volume fraction group at i (e.g. matset/volume_fractions/mat[i]) contains the volume fraction data for topological element i. This variant is assumed in all material sets that don’t have an element_ids child.

The following diagram illustrates a simple element-dominant material set example:

#     z0       z1       z2
# +--------+--------+--------+
# | a0     | a1 ___/|\___ c2 |
# |___-----|----    |    ----|
# |     b0 |     b1 | b2     |
# +--------+--------+--------+
#

matsets:
  matset:
    topology: topology
    volume_fractions:
      a: [a0, a1, 0]
      b: [b0, b1, b2]
      c: [0, 0, c2]
    material_map: # (optional)
      a: 0
      b: 1
      c: 2
Material-Dominant Material Sets

In a material-dominant material set, the orders for the volume fractions and topological elements are mismatched and need to be bridged via indirection arrays. For these schemas, the element_ids field hosts these indirection arrays per material (with just one indirection array for uni-buffer material sets). In explicit terms, the material-dominant volume fraction group at i (e.g. matset/volume_fractions/mat[i]) contains the volume fraction data for the indirected topological element i (e.g. matset/element_ids/mat[i]). Complementary to the element-dominant variant, the material-dominant variant applies to all material sets that have an element_ids child.

The following diagram illustrates a simple material-dominant material set example:

#     z0       z1       z2
# +--------+--------+--------+
# | a0     | a1 ___/|\___ c2 |
# |___-----|----    |    ----|
# |     b0 |     b1 | b2     |
# +--------+--------+--------+
#

matsets:
  matset:
    topology: topology
    volume_fractions:
      a: [a0, a1]
      b: [b0, b1, b2]
      c: [c2]
    element_ids:
      a: [0, 1]
      b: [0, 1, 2]
      c: [2]
    material_map: # (optional)
      a: 0
      b: 1
      c: 2

Fields

Fields are used to hold simulation state arrays associated with a mesh topology and (optionally) a mesh material set.

Each field entry can define an mcarray of material-independent values and/or an mcarray of per-material values. These data arrays must be specified alongside a source space, which specifies the space over which the field values are defined (i.e. a topology for material-independent values and a material set for material-dependent values). Minimally, each field entry must specify one of these data sets, the source space for the data set, an association type (e.g. per-vertex, per-element, or per-grid-function-entity), and a volume scaling type (e.g. volume-dependent, volume-independent). Thus, to conform to protocol, each entry under the fields section must be an Object that adheres to one of the following descriptions:

  • Material-Independent Fields:
    • fields/field/association: “vertex” | “element”
    • fields/field/grid_function: (mfem-style finite element collection name) (replaces “association”)
    • fields/field/volume_dependent: “true” | “false”
    • fields/field/topology: “topo”
    • fields/field/values: (mcarray)
  • Material-Dependent Fields:
    • fields/field/association: “vertex” | “element”
    • fields/field/grid_function: (mfem-style finite element collection name) (replaces “association”)
    • fields/field/volume_dependent: “true” | “false”
    • fields/field/matset: “matset”
    • fields/field/matset_values: (mcarray)
  • Mixed Fields:
    • fields/field/association: “vertex” | “element”
    • fields/field/grid_function: (mfem-style finite element collection name) (replaces “association”)
    • fields/field/volume_dependent: “true” | “false”
    • fields/field/topology: “topo”
    • fields/field/values: (mcarray)
    • fields/field/matset: “matset”
    • fields/field/matset_values: (mcarray)

Topology Association for Field Values

For implicit topologies, the field values are associated with the topology by fast varying logical dimensions starting with i, then j, then k.

For explicit topologies, the field values are associated with the topology by assuming the order of the field values matches the order the elements are defined in the topology.

Species Sets

Species Sets are a means of representing multi-dimensional per-material quantities, most commonly per-material substance fractions.

Individual Species Sets are entries in the specsets section of the Blueprint hierarchy, and these entries are formatted in much the same way as fields entries that describe per-material, multi-dimensional fields. Just as with this class of fields entries, each specsets entry must specify the material set over which it is defined and enumerate its values within an mcarray that’s organized first by materials (shallower level of nesting) and then by species components (deeper level of nesting). Additionally, like field entries, each specsets item must indicate a volumetric scaling type (e.g. volume-dependent, volume-independent). To put it in short, each entry in the specsets section of the Blueprint hierarchy must be an Object that follows this template:

  • specsets/specset/volume_dependent: “true” | “false”
  • specsets/specset/matset: “matset”
  • specsets/specset/matset_values: (mcarray)

Nesting Sets

Nesting Sets are used to represent the nesting relationships between different domains in multi-domain mesh environments. Most commonly, this subset of the Blueprint specification is used for AMR (adaptive mesh refinement) meshes.

Each entry in the Nesting Sets section contains an independent set of nesting relationships between domains in the described mesh. On an individual basis, a nesting set contains a source topology, an element association, and a list of nesting windows. The windows for a particular nesting set describe the topological nesting pattern for a paired set of domains, which includes the ID of the partnered domain, the type of the partnered domain (parent or child), the per-dimension zone ratios of this domain relative to the partnered domain, and the self-relative dimensions and origin (provided in terms of local domain coordinates) of the nesting relationship. The Blueprint schema for each entry in the nestsets section matches the following template:

  • nestsets/nestset/association: “vertex” | “element”
  • nestsets/nestset/topology: “topo”
  • nestsets/nestset/windows/window/domain_id: (integer)
  • nestsets/nestset/windows/window/domain_type: “parent” | “child”
  • nestsets/nestset/windows/window/ratio/{i, j, k}
  • nestsets/nestset/windows/window/origin/{i, j, k}
  • nestsets/nestset/windows/window/dims/{i, j, k}

Note

Many structured AMR codes use global coordinate identifiers when specifying each window’s origin. Such coordinates must be transformed to domain-local coordinates to be Blueprint-compliant. Given the global structured origin of a window’s associated topology topo_origin (which isn’t in the Blueprint, but is likely stored somewhere in the client code), the global origin can be transformed into a local origin like so:

// 'window_origin': starts out as a global index, but is transformed into
// a domain-local index through this procedure
conduit::Node &window_origin = // path to nestset/windows/window/origin
conduit::Node &topo_origin = // loaded from client code; {i, j, k} structure

conduit::NodeIterator origin_it = window_origin.children();
while(origin_it.has_next())
{
    conduit::Node &window_dim = origin_it.next();
    conduit::Node &topo_dim = topo_origin[origin_it.name()];

    conduit::int64 new_dim_val = window_dim.to_int64() - topo_dim.to_int64();
    conduit::Node &new_dim(conduit::DataType::int64(1), &new_dim_val, true);
    new_dim.to_data_type(window_dim.dtype().id(), window_dim);
}

Each domain that contains a Nesting Sets section must also update its State section to include the domain’s global nesting level. This additional requirement adds the follow constraint to the state section:

  • state/level_id: (integer)

Note

The Nesting Sets section currently only supports nesting specifications for structured topologies. There are plans to extend this feature to support unstructured topologies in future versions of Conduit.

Adjacency Sets

Adjacency Sets are used to outline the shared geometry between subsets of domains in multi-domain meshes.

Each entry in the Adjacency Sets section is meant to encapsulate a set of adjacency information shared between domains. Each individual adjacency set contains a source topology, an element association, and a list of adjacency groups. An adjacency set’s contained groups describe adjacency information shared between subsets of domains, which is represented by a subset of adjacent neighbor domains IDs and a list of shared element IDs. The fully-defined Blueprint schema for the adjsets entries looks like the following:

  • adjsets/adjset/association: “vertex” | “element”
  • adjsets/adjset/topology: “topo”
  • adjsets/adjset/groups/group/neighbors: (integer array)
  • adjsets/adjset/groups/group/values: (integer array)

State

Optional state information is used to provide metadata about the mesh. While the mesh blueprint is focused on describing a single domain of a domain decomposed mesh, the state info can be used to identify a specific mesh domain in the context of a domain decomposed mesh.

To conform, the state entry must be an Object and can have the following optional entries:

  • state/time: (number)
  • state/cycle: (number)
  • state/domain_id: (integer)

Mesh Blueprint Examples

The C++ conduit::blueprint::mesh::examples namespace and the Python conduit.blueprint.mesh.examples module provide functions that generate example Mesh Blueprint data. For details on how to write these data sets to files, see the unit tests that exercise these examples in src/tests/blueprint/t_blueprint_mesh_examples.cpp and the mesh output example below. This section outlines the examples that demonstrate the most commonly used mesh schemas.

basic

The simplest of the mesh examples, basic(), generates an homogenous example mesh with a configurable element representation/type (see the mesh_type table below) spanned by a single scalar field that contains a unique identifier for each mesh element. The function that needs to be called to generate an example of this type has the following signature:

conduit::blueprint::mesh::examples::basic(const std::string &mesh_type, // element type/dimensionality
                                          index_t nx,                   // number of grid points along x
                                          index_t ny,                   // number of grid points along y
                                          index_t nz,                   // number of grid points along z (3d only)
                                          Node &res);                   // result container

The element representation, type, and dimensionality are all configured through the mesh_type argument. The supported values for this parameter and their corresponding effects are outlined in the table below:

Mesh Type Dimensionality Coordset Type Topology Type Element Type
uniform 2d/3d implicit implicit quad/hex
rectilinear 2d/3d implicit implicit quad/hex
structured 2d/3d explicit implicit quad/hex
tris 2d explicit explicit tri
quads 2d explicit explicit quad
polygons 2d explicit explicit polygon
tets 3d explicit explicit tet
hexs 3d explicit explicit hex
polyhedra 3d explicit explicit polyhedron

The remainder of this section demonstrates each of the different basic() mesh types, outlining each type with a simple example that (1) presents the generating call, (2) shows the results of the call in Blueprint schema form, and (3) displays the corresponding graphical rendering of this schema.

Uniform

  • Usage Example
// create container node
Node mesh;
// generate simple uniform 2d 'basic' mesh
conduit::blueprint::mesh::examples::basic("uniform", 3, 3, 0, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "uniform"
    dims: 
      i: 3
      j: 3
    origin: 
      x: -10.0
      y: -10.0
    spacing: 
      dx: 10.0
      dy: 10.0
topologies: 
  mesh: 
    type: "uniform"
    coordset: "coords"
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0]
  • Visual
_images/basic_hex_2d_render.png

Pseudocolor plot of basic (mesh type ‘uniform’)

Rectilinear

  • Usage Example
// create container node
Node mesh;
// generate simple rectilinear 2d 'basic' mesh
conduit::blueprint::mesh::examples::basic("rectilinear", 3, 3, 0, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "rectilinear"
    values: 
      x: [-10.0, 0.0, 10.0]
      y: [-10.0, 0.0, 10.0]
topologies: 
  mesh: 
    type: "rectilinear"
    coordset: "coords"
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0]
  • Visual
_images/basic_hex_2d_render.png

Pseudocolor plot of basic (mesh type ‘rectilinear’)

Structured

  • Usage Example
// create container node
Node mesh;
// generate simple structured 2d 'basic' mesh
conduit::blueprint::mesh::examples::basic("structured", 3, 3, 1, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "structured"
    coordset: "coords"
    elements: 
      dims: 
        i: 2
        j: 2
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0]
  • Visual
_images/basic_hex_2d_render.png

Pseudocolor plot of basic (mesh type ‘structured’)

Tris

  • Usage Example
// create container node
Node mesh;
// generate simple explicit tri-based 2d 'basic' mesh
conduit::blueprint::mesh::examples::basic("tris", 3, 3, 0, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "unstructured"
    coordset: "coords"
    elements: 
      shape: "tri"
      connectivity: [0, 3, 4, 0, 1, 4, 1, 4, 5, 1, 2, 5, 3, 6, 7, 3, 4, 7, 4, 7, 8, 4, 5, 8]
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]
  • Visual
_images/basic_tet_2d_render.png

Pseudocolor plot of basic (mesh type ‘tris’)

Quads

  • Usage Example
// create container node
Node mesh;
// generate simple explicit quad-based 2d 'basic' mesh
conduit::blueprint::mesh::examples::basic("quads", 3, 3, 0, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "unstructured"
    coordset: "coords"
    elements: 
      shape: "quad"
      connectivity: [0, 3, 4, 1, 1, 4, 5, 2, 3, 6, 7, 4, 4, 7, 8, 5]
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0]
  • Visual
_images/basic_hex_2d_render.png

Pseudocolor plot of basic (mesh type ‘quads’)

Polygons

  • Usage Example
// create container node
Node mesh;
// generate simple explicit poly-based 2d 'basic' mesh
conduit::blueprint::mesh::examples::basic("polygons", 3, 3, 0, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "unstructured"
    coordset: "coords"
    elements: 
      shape: "polygonal"
      sizes: [4, 4, 4, 4]
      connectivity: [0, 3, 4, 1, 1, 4, 5, 2, 3, 6, 7, 4, 4, 7, 8, 5]
      offsets: [0, 4, 8, 12]
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0]
  • Visual
_images/basic_hex_2d_render.png

Pseudocolor plot of basic (mesh type ‘polygons’)

Tets

  • Usage Example
// create container node
Node mesh;
// generate simple explicit tri-based 3d 'basic' mesh
conduit::blueprint::mesh::examples::basic("tets", 3, 3, 3, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
      z: [-10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "unstructured"
    coordset: "coords"
    elements: 
      shape: "tet"
      connectivity: [0, 4, 1, 13, 0, 3, 4, 13, 0, 12, 3, 13, 0, 9, 12, 13, 0, 10, 9, 13, 0, 1, 10, 13, 1, 5, 2, 14, 1, 4, 5, 14, 1, 13, 4, 14, 1, 10, 13, 14, 1, 11, 10, 14, 1, 2, 11, 14, 3, 7, 4, 16, 3, 6, 7, 16, 3, 15, 6, 16, 3, 12, 15, 16, 3, 13, 12, 16, 3, 4, 13, 16, 4, 8, 5, 17, 4, 7, 8, 17, 4, 16, 7, 17, 4, 13, 16, 17, 4, 14, 13, 17, 4, 5, 14, 17, 9, 13, 10, 22, 9, 12, 13, 22, 9, 21, 12, 22, 9, 18, 21, 22, 9, 19, 18, 22, 9, 10, 19, 22, 10, 14, 11, 23, 10, 13, 14, 23, 10, 22, 13, 23, 10, 19, 22, 23, 10, 20, 19, 23, 10, 11, 20, 23, 12, 16, 13, 25, 12, 15, 16, 25, 12, 24, 15, 25, 12, 21, 24, 25, 12, 22, 21, 25, 12, 13, 22, 25, 13, 17, 14, 26, 13, 16, 17, 26, 13, 25, 16, 26, 13, 22, 25, 26, 13, 23, 22, 26, 13, 14, 23, 26]
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, 16.0, 17.0, 18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, 27.0, 28.0, 29.0, 30.0, 31.0, 32.0, 33.0, 34.0, 35.0, 36.0, 37.0, 38.0, 39.0, 40.0, 41.0, 42.0, 43.0, 44.0, 45.0, 46.0, 47.0]
  • Visual
_images/basic_tet_3d_render.png

Pseudocolor plot of basic (mesh type ‘tets’)

Hexs

  • Usage Example
// create container node
Node mesh;
// generate simple explicit quad-based 3d 'basic' mesh
conduit::blueprint::mesh::examples::basic("hexs", 3, 3, 3, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
      z: [-10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "unstructured"
    coordset: "coords"
    elements: 
      shape: "hex"
      connectivity: [0, 1, 4, 3, 9, 10, 13, 12, 1, 2, 5, 4, 10, 11, 14, 13, 3, 4, 7, 6, 12, 13, 16, 15, 4, 5, 8, 7, 13, 14, 17, 16, 9, 10, 13, 12, 18, 19, 22, 21, 10, 11, 14, 13, 19, 20, 23, 22, 12, 13, 16, 15, 21, 22, 25, 24, 13, 14, 17, 16, 22, 23, 26, 25]
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]
  • Visual
_images/basic_hex_3d_render.png

Pseudocolor plot of basic (mesh type ‘hexs’)

Polyhedra

  • Usage Example
// create container node
Node mesh;
// generate simple explicit poly-based 3d 'basic' mesh
conduit::blueprint::mesh::examples::basic("polyhedra", 3, 3, 3, mesh);
// print out results
mesh.print();
  • Result
coordsets: 
  coords: 
    type: "explicit"
    values: 
      x: [-10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0, -10.0, 0.0, 10.0]
      y: [-10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0]
      z: [-10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, -10.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0, 10.0]
topologies: 
  mesh: 
    type: "unstructured"
    coordset: "coords"
    elements: 
      shape: "polyhedral"
      connectivity: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 2, 10, 11, 3, 12, 13, 14, 15, 16, 9, 17, 18, 12, 19, 5, 20, 21, 22, 23, 24, 10, 25, 26, 27, 21, 28, 15, 22, 29, 30, 31, 32, 19, 27, 33, 34, 29, 35]
      sizes: [6, 6, 6, 6, 6, 6, 6, 6]
      offsets: [0, 6, 12, 18, 24, 30, 36, 42]
    subelements: 
      shape: "polygonal"
      connectivity: [0, 3, 4, 1, 0, 1, 10, 9, 1, 4, 13, 10, 4, 3, 12, 13, 3, 0, 9, 12, 9, 10, 13, 12, 1, 4, 5, 2, 1, 2, 11, 10, 2, 5, 14, 11, 5, 4, 13, 14, 10, 11, 14, 13, 3, 6, 7, 4, 4, 7, 16, 13, 7, 6, 15, 16, 6, 3, 12, 15, 12, 13, 16, 15, 4, 7, 8, 5, 5, 8, 17, 14, 8, 7, 16, 17, 13, 14, 17, 16, 9, 10, 19, 18, 10, 13, 22, 19, 13, 12, 21, 22, 12, 9, 18, 21, 18, 19, 22, 21, 10, 11, 20, 19, 11, 14, 23, 20, 14, 13, 22, 23, 19, 20, 23, 22, 13, 16, 25, 22, 16, 15, 24, 25, 15, 12, 21, 24, 21, 22, 25, 24, 14, 17, 26, 23, 17, 16, 25, 26, 22, 23, 26, 25]
      sizes: [4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4]
      offsets: [0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, 64, 68, 72, 76, 80, 84, 88, 92, 96, 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140]
fields: 
  field: 
    association: "element"
    topology: "mesh"
    volume_dependent: "false"
    values: [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0]
  • Visual
_images/basic_hex_3d_render.png

Pseudocolor plot of basic (mesh type ‘polyhedra’)

braid

_images/braid_render.png

Pseudocolor plot of a 3D braid example braid field

The braid() generates example meshes that cover the range of coordinate sets and topologies supported by the Mesh Blueprint.

The example datasets include a vertex-centered scalar field braid, an element-centered scalar field radial and a vertex-centered vector field vel.

conduit::blueprint::mesh::examples::braid(const std::string &mesh_type,
                                          index_t nx,
                                          index_t ny,
                                          index_t nz,
                                          Node &res);

Here is a list of valid strings for the mesh_type argument:

Mesh Type Description
uniform 2d or 3d uniform grid (implicit coords, implicit topology)
rectilinear 2d or 3d rectilinear grid (implicit coords, implicit topology)
structured 2d or 3d structured grid (explicit coords, implicit topology)
point 2d or 3d unstructured mesh of point elements (explicit coords, explicit topology)
lines 2d or 3d unstructured mesh of line elements (explicit coords, explicit topology)
tris 2d unstructured mesh of triangle elements (explicit coords, explicit topology)
quads 2d unstructured mesh of quadrilateral elements (explicit coords, explicit topology)
tets 3d unstructured mesh of tetrahedral elements (explicit coords, explicit topology)
hexs 3d unstructured mesh of hexahedral elements (explicit coords, explicit topology)

nx, ny, nz specify the number of elements in the x, y, and z directions.

nz is ignored for 2d-only examples.

The resulting data is placed the Node res, which is passed in via reference.

spiral

_images/spiral_render.png

Pseudocolor and Contour plots of the spiral example dist field.

The sprial() function generates a multi-domain mesh composed of 2D square domains with the area of successive fibonacci numbers. The result estimates the Golden spiral.

The example dataset provides a vertex-centered scalar field dist that estimates the distance from each vertex to the Golden spiral.

conduit::blueprint::mesh::examples::spiral(conduit::index_t ndomains,
                                           Node &res);

ndomains specifies the number of domains to generate, which is also the number of entries from fibonacci sequence used.

The resulting data is placed the Node res, which is passed in via reference.

julia

_images/julia_render.png

Pseudocolor plot of the julia example iter field

The julia() function creates a uniform grid that visualizes Julia set fractals.

The example dataset provides an element-centered scalar field iter that represents the number of iterations for each point tested or zero if not found in the set.

conduit::blueprint::mesh::examples::julia(index_t nx,
                                          index_t ny,
                                          float64 x_min,
                                          float64 x_max,
                                          float64 y_min,
                                          float64 y_max,
                                          float64 c_re,
                                          float64 c_im,
                                          Node &res);

nx, ny specify the number of elements in the x and y directions.

x_min, x_max, y_min, y_max specify the x and y extents.

c_re, c_im specify real and complex parts of the constant used.

The resulting data is placed the Node res, which is passed in via reference.

julia amr examples

We also provide examples that represent the julia set using AMR meshes. These functions provide concrete examples of the Mesh Blueprint nestset protocol for patch-based AMR meshes.

_images/julia_nestsets_simple.png

Pseudocolor, Mesh, and Domain Boundary plots of the julia_nestsets_simple example.

conduit::blueprint::mesh::examples::julia_nestsets_simple(float64 x_min,
                                                          float64 x_max,
                                                          float64 y_min,
                                                          float64 y_max,
                                                          float64 c_re,
                                                          float64 c_im,
                                                          Node &res);

julia_nestsets_simple provides a basic AMR example with two levels and one parent/child nesting relationship.

x_min, x_max, y_min, y_max specify the x and y extents.

c_re, c_im specify real and complex parts of the constant used.

The resulting data is placed the Node res, which is passed in via reference.

_images/julia_nestsets_complex.png

Pseudocolor, Mesh, and Domain Boundary plots of the julia_nestsets_complex example.

conduit::blueprint::mesh::examples::julia_nestsets_complex(index_t nx,
                                                           index_t ny,
                                                           float64 x_min,
                                                           float64 x_max,
                                                           float64 y_min,
                                                           float64 y_max,
                                                           float64 c_re,
                                                           float64 c_im,
                                                           index_t levels,
                                                           Node &res);

julia_nestsets_complex provides an AMR example that refines the mesh using more resolution in complex areas.

nx, ny specify the number of elements in the x and y directions.

x_min, x_max, y_min, y_max specify the x and y extents.

c_re, c_im specify real and complex parts of the constant used.

levels specifies the number of refinement levels to use.

The resulting data is placed the Node res, which is passed in via reference.

venn

_images/venn_example.png

Pseudocolor plot of the venn example overlap field

The venn() function creates meshes that use three overlapping circle regions, demonstrating different ways to encode volume fraction based multi-material fields. The volume fractions are provided as both standard fields and using the Material sets (matsets) Blueprint. It also creates other fields related to overlap pattern.

conduit::blueprint::mesh::examples::venn(const std::string &matset_type,
                                         index_t nx,
                                         index_t ny,
                                         float64 radius,
                                         Node &res);

matset_type specifies the style of matset generated by the example.

Here is a list of valid strings for the matset_type argument:

Matset Type Description
full non-sparse volume fractions and matset values
sparse_by_material sparse (material dominant) volume fractions and matset values
sparse_by_element sparse (element dominant) volume fractions and matset values

nx, ny specify the number of elements in the x and y directions.

radius specifies the radius of the three circles.

The resulting data is placed the Node res, which is passed in via reference.

polytess

_images/polytess_render.png

Pseudocolor plot of the polytess example level field, with nz = 1.

_images/polytess_3d_render.png

Pseudocolor plot of the polytess example level field, with nz = 2.

_images/polytess_3d_tall_render.png

Pseudocolor plot of the polytess example level field, with nz = 10.

_images/polytess_3d_big_render.png

Pseudocolor plot of the polytess example level field, with nz = 6.

The polytess() function generates a polygonal tessellation in the 2D plane comprised of octagons and squares (known formally as a two-color truncated square tiling). This can be extended into 3D using the nz parameter, which, if greater than 1, will stack polytessalations on top of one another as follows: first, a polytess is placed into 3D space, and then a copy of it is placed into a plane parallel to the original. Then “walls” are added, and finally polyhedra are specified that use faces from the original polytess, the reflected copy, and the walls. An nz value of 3 or more will simply add layers to this setup, essentially stacking “sheets” of polytess on top of one another.

The scalar element-centered field level defined in the result mesh associates each element with its topological distance from the center of the tessellation.

conduit::blueprint::mesh::examples::polytess(index_t nlevels,
                                             index_t nz,
                                             Node &res);

nlevels specifies the number of tessellation levels/layers to generate. If this value is specified as 1 or less, only the central tessellation level (i.e. the octagon in the center of the geometry) will be generated in the result.

The resulting data is placed the Node res, which is passed in via reference.

polychain

_images/polychain.png

Pseudocolor plot of the polyhedral chain example chain field.

The polychain() function generates a chain of cubes and triangular prisms that extends diagonally.

The scalar element-centered field chain defined in the result mesh associates with each cube the value 0 and with each triangular prism the value 1.

conduit::blueprint::mesh::examples::polychain(const index_t length,
                                              Node &res);

length specifies how long the chain ought to be. The length is equal to the number of cubes and equal to half the number of prisms.

The resulting data is placed the Node res, which is passed in via reference.

miscellaneous

This section doesn’t overview any specific example in the conduit::blueprint::mesh::examples namespace, but rather provides a few additional code samples to help with various common tasks. Each subsection covers a specific task and presents how it can be accomplished using a function or set of functions in Conduit and/or the Mesh Blueprint library.

Outputting Meshes for Visualization

Suppose that you have an arbitrary Blueprint mesh that you want to output from a running code and subsequently visualize using a visualization tool (e.g. VisIt). You can save your mesh to a set of files, using one of the following conduit::relay::io::blueprint library functions:

Save a mesh to disk:

conduit::relay::io::blueprint::write_mesh(const conduit::Node &mesh,
                                          const std::string &path);

Save a mesh to disk using a specific protocol:

conduit::relay::io::blueprint::write_mesh(const conduit::Node &mesh,
                                          const std::string &protocol,
                                          const std::string &path);

Save a mesh to disk using a specific protocol and options:

/// Options accepted via the `opts` Node argument:
///
///      file_style: "default", "root_only", "multi_file"
///            when # of domains == 1,  "default"   ==> "root_only"
///            else,                    "default"   ==> "multi_file"
///
///      suffix: "default", "cycle", "none"
///            when # of domains == 1,  "default"   ==> "none"
///            else,                    "default"   ==> "cycle"
///
///      mesh_name:  (used if present, default ==> "mesh")
///
///      number_of_files:  {# of files}
///            when "multi_file":
///                 <= 0, use # of files == # of domains
///                  > 0, # of files == number_of_files
///
conduit::relay::io::blueprint::write_mesh(const conduit::Node &mesh,
                                          const std::string &path,
                                          const std::string &protocol,
                                          const conduit::Node &opts);

Loading Meshes from Files

If you have a mesh written to a set of blueprint files, you can load them by passing the root file path to the following conduit::relay::io::blueprint library functions:

Load a mesh given a root file:

conduit::relay::io::blueprint::read_mesh(const std::string &root_file_path,
                                         conduit::Node &mesh);

Load a mesh given a root file and options:

/// Options accepted via the `opts` Node argument:
///
///      mesh_name: "{name}"
///          provide explicit mesh name, for cases where bp data includes
///           more than one mesh.
///
conduit::relay::io::blueprint::read_mesh(const std::string &root_file_path,
                                         const conduit::Node &opts,
                                         conduit::Node &mesh);

Complete Uniform Example

This snippet provides a complete C++ example that demonstrates:

  • Describing a single-domain uniform mesh in a Conduit tree
  • Verifying the tree conforms to the Mesh Blueprint
  • Saving the result to a file that VisIt and Ascent Replay can open
// create a Conduit node to hold our mesh data
Node mesh;

// create the coordinate set
mesh["coordsets/coords/type"] = "uniform";
mesh["coordsets/coords/dims/i"] = 3;
mesh["coordsets/coords/dims/j"] = 3;
// add origin and spacing to the coordset (optional)
mesh["coordsets/coords/origin/x"] = -10.0;
mesh["coordsets/coords/origin/y"] = -10.0;
mesh["coordsets/coords/spacing/dx"] = 10.0;
mesh["coordsets/coords/spacing/dy"] = 10.0;

// add the topology
// this case is simple b/c it's implicitly derived from the coordinate set
mesh["topologies/topo/type"] = "uniform";
// reference the coordinate set by name
mesh["topologies/topo/coordset"] = "coords";

// add a simple element-associated field 
mesh["fields/ele_example/association"] =  "element";
// reference the topology this field is defined on by name
mesh["fields/ele_example/topology"] =  "topo";
// set the field values, for this case we have 4 elements
mesh["fields/ele_example/values"].set(DataType::float64(4));

float64 *ele_vals_ptr = mesh["fields/ele_example/values"].value();

for(int i=0;i<4;i++)
{
    ele_vals_ptr[i] = float64(i);
}

// add a simple vertex-associated field 
mesh["fields/vert_example/association"] =  "vertex";
// reference the topology this field is defined on by name
mesh["fields/vert_example/topology"] =  "topo";
// set the field values, for this case we have 9 vertices
mesh["fields/vert_example/values"].set(DataType::float64(9));

float64 *vert_vals_ptr = mesh["fields/vert_example/values"].value();

for(int i=0;i<9;i++)
{
    vert_vals_ptr[i] = float64(i);
}

// make sure we conform:
Node verify_info;
if(!blueprint::mesh::verify(mesh, verify_info))
{
    std::cout << "Verify failed!" << std::endl;
    verify_info.print();
}

// print out results
mesh.print();

// save our mesh to a file that can be read by VisIt
//
// this will create the file: complete_uniform_mesh_example.root
// which includes the mesh blueprint index and the mesh data
conduit::relay::io::blueprint::save_mesh(mesh,
                                         "complete_uniform_mesh_example",
                                         "json");

Expressions (Derived Fields)

An expression is a mathematical formula which defines a new field in terms of other fields and/or other expressions. Expressions are specified in the expressions section of the Blueprint protocol. The expressions section is optional. When it exists, it is a peer to the fields section. It is a list of Objects of the form:

  • expressions/expression/number_of_components
  • expressions/expression/topology
  • expressions/expression/definition

The number_of_components and topology entries are identical to their meaning as entries in the fields section.

The definition entry is string valued and holds the expression (e.g. mathematical formula) defining how the new field is computed. Blueprint does not interpret this string. It simply passes it along for downstream consumers that have the ability to interpret the string and perform the associated operations to compute the expression.

If the expected consumer is VisIt, data producers may wish to consult the Expressions chapter of the VisIt user’s manual. In addition, data producers should escape all names of fields or expressions by bracketing them in < and > characters. An example expressions entry in the index is

"fields":
{
  "braid":
  {
    ...
  },
  "radial":
  {
    ...
  },
"expressions":
{
  "scalar_expr":
  {
    "number_of_components": 1,
    "topology": "mesh",
    "definition": "<vector_expr>[1]"
  },
  "vector_expr":
  {
    "number_of_components": 2,
    "topology": "mesh",
    "definition": "{<braid>,recenter(<radial>,\"nodal\")}"
  }
}