private PointList getQuarter(final double minX, final double maxX, final double minY, final double maxY) {
		final PointList result = new PointList(this.size(), minX, maxX, minY, maxY);
		for (final float[] p : this.points) {
			if (p[0] >= minX && p[0] < maxX && p[1] >= minY && p[1] < maxY) {
				result.add(p[0], p[1]);
			}
		}
		result.trim();
		return result;
	}