Re: [Geotools-gt2-users] Graph neighbors as edges

[Jody G. <jod...@gm...>]

> Hi Jody,
> Yes, I have looked at the wiki! The wiki only mentions the "touches"
> relationship. It doesn't show you how to extract this "touches" property in
> the shapefile.

You need to look at the Geometry class to sort out the different
relationships. touches is a method on the geometry class (ie Polygon).

> So, I need to know how to find out from a shapefile if two
> polygons are touching. This is the question that I am trying to answer.

Thinking - are you talking the graph module here (that is do you want
to build a network) or are you just trying to find matches?

You may wish to use a for loop and go through the shapefile multiple times;
- it take one polygon out ,,,
- use it to query the  shapefile a second time to find other polygons that touch
- continue ...

Reading:
- http://docs.codehaus.org/display/GEOTDOC/06+FeatureSource
- http://docs.codehaus.org/display/GEOTDOC/12+Using+a+Loop+to+Join+FeatureCollections

> Another question, what is the difference between a 4 points ploygon and a 5?
>
> Polygon p1 = createPolygon("0 0,1 1,2 2,0 0");// 4 points
> Polygon p2 = createPolygon("0 0,5 0,5 5,0 5,0 0"); // 5 points

Not sure I understand  they are two different polygons...

For background reading on how geometry comparisons are performed:
- http://docs.codehaus.org/display/GEOTDOC/03+JTS+Topology+Suite
- http://docs.codehaus.org/display/GEOTDOC/Point+Set+Theory+and+the+DE-9IM+Matrix