[R-sig-Geo] Queen, Rook and Knight neighbours

[christiaan pauw]

Hi Everybody

Is there a possibility to create a neighbourhood list with a custom
contiguity condition? There is queen and rook contiguity but I need
something which may be called "Knight" : i.e. skip two (in a certain
direction) and choose the next one.

Here is my problem: I have a multi-stage sampling plan for a household
survey. This involves defining street blocks from a SPDF of houses
(which thanks to the help of Roger on this list I am now able to do
using poly2nb and n.comp.nb), then selecting a number of random street
blocks where the survey will take place. In each block we  take a
random starting point and move around the block and interview every
third household from until we reach the starting point again.

I need to make a neighbourhood list which will give me these every
third house in a certain direction from the starting point. This means
the contiguity condition would be something like:
"skip the house to the left, skip the house to its left , take the
house to its left and select it, repeat until you reach a number that
has already been evaluated then stop.

I would appreciate any ideas

best regards
Christiaan