Data hierarchy refers to the four types of data (called entities) you will work with during the construction of your grid. Pointwise organizes the entities into four types:
- Database: Geometry data that defines the shape of the object being gridded
The data hierarchy's foundation is the database: a geometry model of the object on and around which a grid is to be generated. You typically obtain the
database from a computer aided design (CAD) system and import it into Pointwise. Pointwise also provides tools for creating database entities. A database can
consist of points, curves, surfaces and other topological data like trimmed surfaces. Keep in mind, however, that Pointwise does not require a database; the
geometry of the grid entities you create may implicitly define the grid's shape. Furthermore, Pointwise does not require the database to represent a closed
solid model, it can use CAD models with gaps and overlaps in them.
Tip: Because Pointwise maintains hierarchical relationships between grid and database entities, it can automate many parts of the
grid generation process.
The remaining three elements of Pointwise's hierarchy are the grid entities: connectors (curve grids), domains (surface grids), and blocks (volume
grids). Grid entities are ordered according to their computational dimension. Note, however, that all of Pointwise's grid entities may have a 3D shape (i.e.
all three components of the Cartesian coordinates (x,y,z) may vary).
Connectors, the grid entity at the bottom of the hierarchy, are curves on which grid points are distributed. A connector, what a CAD system would call a
composite curve, consists of one or more segments. Segments are basic curve types, which can be polylines, polycurves, conics and circles, or curves obtained
from a database.
The grid entity in the middle of the hierarchy is the domain, a surface grid. An initial domain grid is generated automatically using a default method when
the domain is first created. A variety of grid methods can then be applied to improve the grid's quality.
Volume grids, called blocks, are at the top of the data hierarchy. As with domains, the initial block grid is created automatically, and a variety of grid
methods may then be applied to improve the grid's quality.
This data hierarchy provides the framework by which modifications to any entity are propagated throughout the rest of the hierarchy. For example,
modification of a connector's shape will update all domains and blocks that use it. The term "forward editing" refers to grid changes propagated up the
hierarchy while "backward editing" refers to downward propagating changes. Pointwise's data hierarchy and forward and backward editing allow you to change one
entity of your grid and have Pointwise make the entire grid system consistent with your change.