Overview

  In the SPARTA system, objects of interest, such as a lake or an area which contains housing, are represented by a name and a set of tesseral addresses, in Morton sequence, which describes where they are or where it is possible for them to be.

Spatial problems are presented to the SPARTA system in the form of scripts comprising a set of object declarations and a set of constraints. For example, given an area such as the Wirral peninsula in Merseyside, bounded partly by the rivers Mersey and Dee and the Irish Sea, and comprised of urban and rural areas, it can be represented as shown in Figure 3 as a set of objects such as:

object water [location]

object urban [location]

object rural [location]

object M53 [location]

object NewRoad [shape] [location]

where the shape and location of the object are comprised of sets of tesseral addresses.

 
Figure 3:   Tesseral Map of The Wirral

The shape of the object (omitted where the location of an object is known) may be presented to the system as one of the following constructs, or as a combination of one or more:

• A single tesseral address, which represents one tile.

• A sequence of tesseral addresses defined by a start and an end address, for example: [010..021] which includes addresses 010,011,012,013,020 and 021.

• A box of tesseral addresses, defined by the bottom left and top right corner addresses (box 001 012).
• A line of addresses defined by its two end addresses (line 0011 0312).

• A circle of addresses, defined by a tile whose centroid is the centre of the circle, and an address which represents the radius, measured by its distance from the tile zero. (circle 0312 0010 represents a circle centred on tile 0312 with a rad ius of 2 tiles.)

The shape of an object is defined with reference to the origin of the object space, which is the zero tile, so that the minimum bounding box of the shape is placed with its bottom left corner at zero. The location of the object is its actual position in the space, if known absolutely, or its possible locations where more than one possibility exists, in the form of Morton-ordered lists. Such a linear storage structure facilitates simple comparison of locations.