Specifies the order in which attribute value records are assigned to
GridPoint.
There are several sequencing rules based on incrementing - or decrementing - grid coordinate values in
a simple fashion. More complex space filling curves can also be used. Space filling curves are generated
by progressively subdividing a space in a regular way and connecting the elements resulting from each
subdivision according to some rule. They can be used to generate a grid, but they can also be used to
assign an ordering to the grid points or grid cells in a separately defined grid. They lend themselves
more readily than simple incrementing methods to sequencing in grids that have irregular shapes or cells
of variable size.
In every case, ordering of the grid cells starts by incrementing coordinates along one grid axis.
At some point in the process, it begins to increment coordinates along a second grid axis, then a
third, and so on until it has progressed in the direction of each of the grid axes. The attribute
SequenceRule#getScanDirection provides a list of signed axis names
that identifies the order in which scanning takes place. The list may include an additional element
to support interleaving of feature attribute values.
Ordering is continuous if consecutive pairs of grid cells in the sequence are maximally connected.
It is semicontinuous if consecutive pairs of grid cells are connected, but less than maximally
connected, and discontinuous if consecutive pairs of cells are not connected.
Example: In the two dimensional case, a cell is connected to the 8 cells with which it
shares at least one corner. It is maximally connected to the 4 cells with which it shares an
edge and two corners. In the three dimensional case, a cell is maximally connected to those
cells with which it shares a face.