JTS Topology Suite

On Mon, Nov 19, 2012 at 6:43 PM, Martin Davis <mtnclimb@...> wrote:

>
> Another option is to simply using Geometry.union() (Unary union).  When
> executed on a collection of LineStrings, this has the effect of noding them
> and dissolving any common linework.  Be aware however that currently JTS
> overlay operations have a small robustness issue, so that if the input
> linework contains line segments that are almost coincident they may not in
> fact be noded quite correctly.
>
>
Duly noted.  Thanks!

I've a follow up question: Given a set of line strings that have been
properly noded, what is the best approach to finding the points
corresponding to their intersections?  One brute force approach would be to
pull out their coordinate strings and note the points that occur more than
once.  That works, but my intuition is that there may be a slick "JTS Way"
that would give me those points in one go.  If so, how would I use JTS to
give me those intersection vertices?

Here's an example of the brute force approach:

            // brokenUpLines contains noded line strings
            Coordinate [] vertices = brokenUpLines.getCoordinates();


            Set<Coordinate> intersectionVertices = new
HashSet<Coordinate>();
            Set<Coordinate> visitedCoordinates = new HashSet<Coordinate>();

            for (int i = 0; i < vertices.length; i++)
            {
                if (! visitedCoordinates.contains(vertices[i]))
                {
                    visitedCoordinates.add(vertices[i]);
                } else // intersection if vertex visited more than once
                {
                    intersectionVertices.add(vertices[i]);
                }
            }

            for (Coordinate c : intersectionVertices.toArray(new
Coordinate[0]))
            {
                System.out.println(c);
            }


Cheers!

Mark