Model Property System

In addition to associating modeling entities with attributes, SMTK’s model resource uses the resource’s properties mechanism to store string, integer, and floating-point properties on model entities. Unlike attributes that have a rigid format imposed by definitions, properties are free-form: given any model entity UUID and a property name, you may store any combination of string, integer, and floating-point values.

The intent of the model property system is two-fold:

1. Properties can be created by sessions to expose modeling-kernel data that cannot otherwise be expressed by SMTK. An example of this is the Exodus session, which stores the Exodus ID of each block and set it reads so that exporters can refer to them as they exist in the file.

2. Properties can be created by applications built on SMTK to mark up model entities. This might include user markup such as entity names or application data such as whether an entity is currently selected, or which views an entity should be displayed in.

Despite being free-form, SMTK does use the property system itself and so some property names are reserved for particular use. The list of these names is below and is followed by properties provided by existing sessions.

Reserved model properties

The following table lists the conventions that SMTK uses for property names. These names are used for the purpose described but the convention is not enforced programmatically.

Properties that applications will most commonly expose to users are summarized in the table below:

Property name	Property type	Description
color	Float	A 3- or 4-tuple holding RGB or RGBA color values. Clamped to [0,1]. An example would be [0., 0., 1., 1.] for blue. Color may be assigned to any entity with a visual representation.
embedding dimension	Integer	The number of coordinates required to represent any point in the locus of all points contained in the entity’s underlying space.
name	String	The name for the entity as presented to the user.
url	String	Assigned to model entities loaded from data at the specified location.

Properties used internally are in the following table:

Property name	Property type	Description
cell_counters	Integer	An array of 6 integers assigned to each model entity and used to generate model-unique names that are easier to read than UUIDs. See Entity::defaultNameFromCounters() to understand how the array is used.
generate normals	Integer	When non-zero, this indicates that the given entity’s tessellation should have surface normals added via approximation (because the modeling kernel does not provide any and the geometry has curvature). When not defined, it is assumed to be zero. When defined, it should be a single value. Most commonly this is stored on models and is applied to all of the tessellated entities belonging to the model. However, it may be stored on individual entities as well.
group_counters	Integer	An array of 3 integers assigned to each model entity and used to generate model-unique names that are easier to read than UUIDs. Three integers are used because groups with the MODEL_DOMAIN or MODEL_BOUNDARY bits set are numbered separately. See Entity::defaultNameFromCounters() to understand how the array is used.
instance_counters	Integer	A single integer assigned to each model entity and used to generate model-unique instance names that are easier to read than UUIDs. See Entity::defaultNameFromCounters() to understand how the counter is used.
invalid_counters	Integer	A single integer assigned to each model entity and used to number invalid child entities in a way that is easier to read than UUIDs. See Entity::defaultNameFromCounters() to understand how the counter is used.
model_counters	Integer	A single integer assigned to each model entity and used to generate a unique name for each submodel of the given model. See Entity::defaultNameFromCounters() to understand how the counter is used.
session pedigree	String or Integer	A session-specific persistent identifier assigned to the associated entity for use by the exporter and other tasks that need to refer to the entity when it is not possible to use UUIDs created by SMTK to do so. This happens when the original model file may not be modified and simulation input decks must refer to entities in that original file. Sessions should provide 0 or 1 values for each entity.
shell_counters	Integer	An array of 5 integers assigned to each model entity and used to generate model-unique names that are easier to read than UUIDs. See Entity::defaultNameFromCounters() to understand how the array is used.
use_counters	Integer	An array of 6 integers assigned to each model entity and used to generate model-unique names that are easier to read than UUIDs. See Entity::defaultNameFromCounters() to understand how the array is used.
_tessgen	Integer	An integer used as a generation number for tessellation and bounding box data; it is incremented each time the entity geometry changes.
_meshgen	Integer	An integer used as a generation number for mesh data; it is incremented each time a mesh is modified (e.g., by displacing it, not by remeshing).
_geomstyle	Integer	Indicates whether the modeling kernel represents geometry discretely (smtk::model::DISCRETE) or parametrically (smtk::model::PARAMETRIC).
_boundingBox	Float	The world-coordinate, axis-aligned bounds of an entity, reported as a 6-vector: [xmin, xmax, ymin, ymax, zmin, zmax].

Model properties of sessions

In general, sessions should choose a prefix for their property names so that developers can easily identify the source of the property, even when saved in a JSON model file. The exception to this rule is properties that should be universal across sessions, such as pedigree ID.

Properties specific to the Exodus session are listed in the table below.

Property name	Property type	Description
cmb id	Integer	A pedigree ID assigned to model entities in discrete sessions.
exodus id	Integer	The block ID or set ID as stored in the Exodus file.
exodus type	String	One of “block”, “side set”, or “node set”. This indicates how the group is represented in the exodus file. The group’s dimension bits can also be used to determine this information by comparing them to the parent model’s parametric dimension.