I’m using NetTopologySuite and have a lot of lines in a List<LineString> and would like to group them in List<MultiLineString>. Every MultiLineString should contain the LineStrings which are connected to each other (i. e. share at least one coordinate) or crossing each other.

I’m thinking of a method like:

List<MultiLineString> GroupLineStrings(List<LineString> lineStrings)
{
    multiLineStrings = new List<MultilineString>();
 
    // ...
 
    return multiLineStrings;
}

I have tried the following:

public static List<LineString> GetConnectedLineStrings(List<LineString> lineStrings)
{
    var visited = new HashSet<LineString>();
    var lineNetworks = new List<LineString>();

    foreach (var lineString in lineStrings)
    {
        if (!visited.Contains(lineString))
        {
            var connectedLines = new List<LineString>();
            DFS(lineString, lineStrings, visited, connectedLines);
            lineNetworks.Add(lineString);
        }
    }

    return lineNetworks;
}

private static void DFS(LineString currentLine, List<LineString> allLines, HashSet<LineString> visited, List<LineString> connectedLines)
{
    visited.Add(currentLine);
    connectedLines.Add(currentLine);

    foreach (var nextLine in GetConnectedLines(currentLine, allLines))
    {
        if (!visited.Contains(nextLine))
        {
            DFS(nextLine, allLines, visited, connectedLines);
        }
    }
}

private static List<LineString> GetConnectedLines(LineString line, List<LineString> allLines)
{
    var connectedLines = new List<LineString>();

    foreach (var otherLine in allLines)
    {
        if (!line.Equals(otherLine) && AreConnected(line, otherLine))
        {
            connectedLines.Add(otherLine);
        }
    }

    return connectedLines;
}

private static bool AreConnected(LineString line1, LineString line2)
{
    // Check if any point from line1 is contained within line2
    for (int i = 0; i < line1.NumPoints; i++)
    {
        if (line2.Contains(line1.GetPointN(i)))
        {
            return true;
        }
    }

    // Check if any point from line2 is contained within line1
    for (int i = 0; i < line2.NumPoints; i++)
    {
        if (line1.Contains(line2.GetPointN(i)))
        {
            return true;
        }
    }

    return false;
}

The result is unfortunately false.