Ordnance Survey geo helper functions

[adamfowleruk]

EPSG:27700 aka UK National Grid uses decimal metres eastings and northings as coordinates. Most OS datasets are accurate to the centimetre.
MarkLogic RAW co-ordinate system works well with this.

Functions may be needed as convenience functions. E.g.:-

• convert to from UK Nat Grid, SK123456 (6, 8, 10 figure grid references), EPSG:4326, EPSG:900913, ETRS89
• distance between two points
• area of polygon / bounding box / point radius