Components

There are many different types of component. Some are mandatory, but most are optional. Only a few of the more common ones are relevant to the present discussion. They are listed in Table  and described below.

Table: Common components of a field.

Name	Mandatory?	Comments
positions	$\bullet$	position of each datum
data	$\bullet$	value of each datum
connections		relation between data points
box		bounding box for positions in the field

Positions

The position component is an array⁹ defining a position for every datum in the dataset. If the field contains unconnected particle data then the array will be a simple list with a position for each datum. If the field contains a regular grid the positions can be represented more compactly as a regular or product array; essentially just the origin, size and increment of the grid are stored.

Data

The data component is an array storing the dependent variable: temperature, density, velocity, momentum or whatever.

Connections

The connections component prescribes to DX how to perform interpolation between neighbouring grid elements. It is described further in Section , below. In unstructured particle or catalogue data the connection component is absent (because the position of one particle bears no relation to the position of any other particle; think of the example of stars following their individual orbits within a globular cluster).

Box

The box component is an array of $2^{n}$ points where $n$ is the dimensionality of the positions component. The values contain the coordinates of a bounding box sufficiently large to just enclose all the positions of a field.