Document Layout Analysis - IPageSegmenter, Docstrum

- Create a TextBlock class
- Creates IPageSegmenter
- Add other useful distances: angle, etc.
- Update RecursiveXYCut
 - With IPageSegmenter and TextBlock
 - Make XYNode and XYLeaf internal
- Optimise (faster) NearestNeighbourWordExtractor and isolate the clustering algorithms for use outside of this class
- Implement a Docstrum inspired page segmentation algorithm

src/UglyToad.PdfPig/Content/TextBlock.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UglyToad.PdfPig.Geometry;
+
+namespace UglyToad.PdfPig.Content
+{
+    /// <summary>
+    /// A block of text.
+    /// </summary>
+    public class TextBlock
+    {
+        /// <summary>
+        /// The text of the block.
+        /// </summary>
+        public string Text { get; }
+
+        /// <summary>
+        /// The text direction of the block.
+        /// </summary>
+        public TextDirection TextDirection { get; }
+
+        /// <summary>
+        /// The rectangle completely containing the block.
+        /// </summary>
+        public PdfRectangle BoundingBox { get; }
+
+        /// <summary>
+        /// The text lines contained in the block.
+        /// </summary>
+        public IReadOnlyList<TextLine> TextLines { get; }
+
+        /// <summary>
+        /// Create a new <see cref="TextBlock"/>.
+        /// </summary>
+        /// <param name="lines"></param>
+        public TextBlock(IReadOnlyList<TextLine> lines)
+        {
+            if (lines == null)
+            {
+                throw new ArgumentNullException(nameof(lines));
+            }
+
+            if (lines.Count == 0)
+            {
+                throw new ArgumentException("Empty lines provided.", nameof(lines));
+            }
+
+            TextLines = lines;
+
+            Text = string.Join(" ", lines.Select(x => x.Text));
+
+            var minX = lines.Min(x => x.BoundingBox.Left);
+            var minY = lines.Min(x => x.BoundingBox.Bottom);
+            var maxX = lines.Max(x => x.BoundingBox.Right);
+            var maxY = lines.Max(x => x.BoundingBox.Top);
+            BoundingBox = new PdfRectangle(minX, minY, maxX, maxY);
+
+            TextDirection = lines[0].TextDirection;
+        }
+
+        /// <inheritdoc />
+        public override string ToString()
+        {
+            return Text;
+        }
+    }
+}