Linear Referencing in SQL Server 2008

Jan 222011

imageLinear referencing is used to define features in relation to existing line features. These new features can either be points or lines. For example a water monitoring station can be defined as 300m along a section of river, or a stretch of road can be defined as requiring repairs, from 220m along to 270m along. Most GISs implement this functionality – for details look at the ESRI and GRASS help pages.

In terms of storing linear referenced point features, you only need three fields – an ID of the original line feature, an ID of the  feature to reference along the line, and a M value – the measurement along the original feature. Line features require two measurement fields, a starting distance, and an end distance.

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The Seven Bridges of Königsberg

Mar 292010

..or do geodevelopers require mathematics?

MyCircle.Area seems simpler.. Alan Skorkin has a great post on “you don’t need math skills to be a good developer but you do need them to be a great one.” Geo-technology developers have similar requirements, and the majority of GISs revolve around CRUD operations. However due to the nature of spatial data we occasionally get to meddle in the world’s of projections, geometry, typology, and set theory more than our counterparts in other sectors.

The Ancient Mysteries

There are now five bridges in Königsberg..Whilst concentrating on algorithms and recursion is a definite benefit to all developers, us spatial developers need a few more specific tricks.  Euler’s 1736 paper on Seven Bridges of Königsberg is one of the first academic writings on modern topology. The titles of these mathematics puzzles create an aura of mysteriousness and arcane knowledge that definitely sweetens the somewhat dour algebra underneath.

The solution (or non-solution) to this problem underpins many of the more advanced techniques used by GIS packages today. The “Travelling Salesman”, whilst conjuring up less interesting images, relies on similar principles of graph theory. Continue reading »