Gaussian smoothing and new geometry densifier

[jgaffuri]

I have developed these two algos which might be interested to be included in jts-core:

• One to smooth geometries using a gaussian kernel
• An other (which is used by the previous) to densify a geometry using a strategy different than the one used in the current Densifier class. A called it "little thumbling" strategy.

This is my first pull to JTS - let me know if I do it properly !

Signed-off-by: jgaffuri jgaf@protonmail.com

[jgaffuri]

This relates to: https://gis.stackexchange.com/questions/326779/

[micycle1]

@jgaffuri I've incorporated your gaussian smoothing implementation into this computational geometry project.

[jgaffuri]

Great job ! Thank you for your interest.

[micycle1]

I'd note that the smoothing outcome is slightly sensitive to the vertex order of the input (i.e. which vertex the coordinate list begins at).

For me this isn't desirable so I use the code below to first normalise vertex order before smoothing.

But perhaps the algorithm itself can be tweaked instead?

	private static LineString normalise(LineString line) {
		boolean isClosed = line.isClosed();

		Coordinate[] originalCoords = line.getCoordinates();
		if (isClosed && originalCoords[0].equals2D(originalCoords[originalCoords.length - 1])) {
			// Remove last vertex if it is a duplicate of the first for closed lines
			originalCoords = Arrays.copyOf(originalCoords, originalCoords.length - 1);
		}

		// Find index of coordinate with smallest x value, tie by y value
		int minIndex = 0;
		for (int i = 1; i < originalCoords.length; i++) {
			if (originalCoords[i].x < originalCoords[minIndex].x
					|| (originalCoords[i].x == originalCoords[minIndex].x && originalCoords[i].y < originalCoords[minIndex].y)) {
				minIndex = i;
			}
		}

		// Rotate array to start from vertex with smallest x (and y, if tied)
		Coordinate[] rotatedCoords = new Coordinate[originalCoords.length + (isClosed ? 1 : 0)];
		System.arraycopy(originalCoords, minIndex, rotatedCoords, 0, originalCoords.length - minIndex);
		System.arraycopy(originalCoords, 0, rotatedCoords, originalCoords.length - minIndex, minIndex);

		if (isClosed) {
			rotatedCoords[rotatedCoords.length - 1] = rotatedCoords[0]; // Close the loop
		}

		return line.getFactory().createLineString(rotatedCoords);
	}