Addind Document Layout Analysis:

- Nearest Neighbour Word Extractor
- Recursive X-Y Cut algorithm, useful for multi-column pdf documents

src/UglyToad.PdfPig.Tests/PublicApiScannerTests.cs

@@ -51,6 +51,10 @@
                 "UglyToad.PdfPig.CrossReference.CrossReferenceTable",
                 "UglyToad.PdfPig.CrossReference.CrossReferenceType",
                 "UglyToad.PdfPig.CrossReference.TrailerDictionary",
+                "UglyToad.PdfPig.DocumentLayoutAnalysis.Distances",
+                "UglyToad.PdfPig.DocumentLayoutAnalysis.MathExtensions",
+                "UglyToad.PdfPig.DocumentLayoutAnalysis.NNWordExtractor",
+                "UglyToad.PdfPig.DocumentLayoutAnalysis.RecursiveXYCut",
                 "UglyToad.PdfPig.Exceptions.PdfDocumentEncryptedException",
                 "UglyToad.PdfPig.Exceptions.PdfDocumentFormatException",
                 "UglyToad.PdfPig.Fonts.DescriptorFontFile",

src/UglyToad.PdfPig/DocumentLayoutAnalysis/Distances.cs

@@ -0,0 +1,86 @@
+using System;
+using System.Linq;
+using UglyToad.PdfPig.Geometry;
+
+namespace UglyToad.PdfPig.DocumentLayoutAnalysis
+{
+    /// <summary>
+    /// Contains helpful tools for distance measures.
+    /// </summary>
+    public static class Distances
+    {
+        /// <summary>
+        /// The Euclidean distance is the "ordinary" straight-line distance between two points.
+        /// </summary>
+        /// <param name="point1">The first point.</param>
+        /// <param name="point2">The second point.</param>
+        /// <returns></returns>
+        public static double Euclidean(PdfPoint point1, PdfPoint point2)
+        {
+            double dx = (double)(point1.X - point2.X);
+            double dy = (double)(point1.Y - point2.Y);
+            return Math.Sqrt(dx * dx + dy * dy);
+        }
+
+        /// <summary>
+        /// The weighted Euclidean distance.
+        /// </summary>
+        /// <param name="point1">The first point.</param>
+        /// <param name="point2">The second point.</param>
+        /// <param name="wX">The weight of the X coordinates. Default is 1.</param>
+        /// <param name="wY">The weight of the Y coordinates. Default is 1.</param>
+        /// <returns></returns>
+        public static double WghtdEuclidean(PdfPoint point1, PdfPoint point2, double wX = 1.0, double wY = 1.0)
+        {
+            double dx = (double)(point1.X - point2.X);
+            double dy = (double)(point1.Y - point2.Y);
+            return Math.Sqrt(wX * dx * dx + wY * dy * dy);
+        }
+
+        /// <summary>
+        /// The Manhattan distance between two points is the sum of the absolute differences of their Cartesian coordinates.
+        /// <para>Also known as rectilinear distance, L1 distance, L1 norm, snake distance, city block distance, taxicab metric.</para>
+        /// </summary>
+        /// <param name="point1">The first point.</param>
+        /// <param name="point2">The second point.</param>
+        /// <returns></returns>
+        public static double Manhattan(PdfPoint point1, PdfPoint point2)
+        {
+            return (double)(Math.Abs(point1.X - point2.X) + Math.Abs(point1.Y - point2.Y));
+        }
+
+        /// <summary>
+        /// Find the nearest point.
+        /// </summary>
+        /// <param name="pdfPoint">The reference point, for which to find the nearest neighbour.</param>
+        /// <param name="points">The list of neighbours candidates.</param>
+        /// <param name="measure">The distance measure to use.</param>
+        /// <param name="dist">The distance between reference point, and its nearest neighbour</param>
+        /// <returns></returns>
+        public static PdfPoint FindNearest(this PdfPoint pdfPoint, PdfPoint[] points,
+            Func<PdfPoint, PdfPoint, double> measure, out double dist)
+        {
+            double d = points.Min(k => measure(k, pdfPoint));
+            PdfPoint point = points.First(x => measure(x, pdfPoint) == d);
+            dist = d;
+            return point;
+        }
+
+        /// <summary>
+        /// Find the index of the nearest point.
+        /// </summary>
+        /// <param name="pdfPoint">The reference point, for which to find the nearest neighbour.</param>
+        /// <param name="points">The list of neighbours candidates.</param>
+        /// <param name="measure">The distance measure to use.</param>
+        /// <param name="dist">The distance between reference point, and its nearest neighbour</param>
+        /// <returns></returns>
+        public static int FindIndexNearest(this PdfPoint pdfPoint, PdfPoint[] points,
+            Func<PdfPoint, PdfPoint, double> measure, out double dist)
+        {
+            double d = points.Min(k => measure(k, pdfPoint));
+            int index = Array.FindIndex(points, x => measure(x, pdfPoint) == d);
+            dist = d;
+            return index;
+        }
+    }
+}

src/UglyToad.PdfPig/DocumentLayoutAnalysis/MathExtensions.cs

@@ -0,0 +1,32 @@
+using System.Collections.Generic;
+using System.Linq;
+
+namespace UglyToad.PdfPig.DocumentLayoutAnalysis
+{
+    /// <summary>
+    /// Useful math extensions.
+    /// </summary>
+    public static class MathExtensions
+    {
+        /// <summary>
+        /// Computes the mode of a sequence of float values.
+        /// </summary>
+        /// <param name="array"></param>
+        /// <returns></returns>
+        public static float Mode(this IEnumerable<float> array)
+        {
+            if (array == null || array.Count() == 0) return float.NaN;
+            return array.GroupBy(v => v).OrderByDescending(g => g.Count()).First().Key;
+        }
+
+        /// <summary>
+        /// Computes the mode of a sequence of decimal values.
+        /// </summary>
+        /// <param name="array"></param>
+        /// <returns></returns>
+        public static decimal Mode(this IEnumerable<decimal> array)
+        {
+            return array.GroupBy(v => v).OrderByDescending(g => g.Count()).First().Key;
+        }
+    }
+}

src/UglyToad.PdfPig/DocumentLayoutAnalysis/NNWordExtractor.cs

@@ -0,0 +1,200 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using UglyToad.PdfPig.Content;
+using UglyToad.PdfPig.Geometry;
+using UglyToad.PdfPig.Util;
+
+namespace UglyToad.PdfPig.DocumentLayoutAnalysis
+{
+    /// <summary>
+    /// Nearest Neighbour Word Extractor, using the <see cref="Distances.Manhattan"/> distance.
+    /// This implementation leverages bounding boxes.
+    /// </summary>
+    public class NNWordExtractor : IWordExtractor
+    {
+        /// <summary>
+        /// Create an instance of Nearest Neighbour Word Extractor, <see cref="NNWordExtractor"/>.
+        /// </summary>
+        public static IWordExtractor Instance { get; } = new NNWordExtractor();
+
+        /// <summary>
+        /// Gets the words.
+        /// </summary>
+        /// <param name="letters"></param>
+        /// <returns></returns>
+        public IEnumerable<Word> GetWords(IReadOnlyList<Letter> letters)
+        {
+            List<Word> wordsH = GetWords(
+                letters.Where(l => l.TextDirection == TextDirection.Horizontal),
+                l => l.GlyphRectangle.Width, Distances.Manhattan)
+                .OrderByDescending(x => x.BoundingBox.Bottom)
+                .ThenBy(x => x.BoundingBox.Left).ToList();
+
+            List<Word> words180 = GetWords(
+                letters.Where(l => l.TextDirection == TextDirection.Rotate180),
+                l => l.GlyphRectangle.Width, Distances.Manhattan)
+                .OrderBy(x => x.BoundingBox.Top)
+                .ThenByDescending(x => x.BoundingBox.Right).ToList();
+            wordsH.AddRange(words180);
+
+            List<Word> words90 = GetWords(
+                letters.Where(l => l.TextDirection == TextDirection.Rotate90),
+                l => l.GlyphRectangle.Height, Distances.Manhattan)
+                .OrderByDescending(x => x.BoundingBox.Left)
+                .ThenBy(x => x.BoundingBox.Top).ToList();
+            wordsH.AddRange(words90);
+
+            List<Word> words270 = GetWords(
+                letters.Where(l => l.TextDirection == TextDirection.Rotate270),
+                l => l.GlyphRectangle.Height, Distances.Manhattan)
+                .OrderBy(x => x.BoundingBox.Right)
+                .ThenByDescending(x => x.BoundingBox.Bottom).ToList();
+            wordsH.AddRange(words270);
+
+            List<Word> wordsU = GetWords(
+                letters.Where(l => l.TextDirection == TextDirection.Unknown),
+                l => l.GlyphRectangle.Width, Distances.Manhattan)
+                .OrderByDescending(x => x.BoundingBox.Bottom)
+                .ThenBy(x => x.BoundingBox.Left).ToList();
+            wordsH.AddRange(wordsU);
+
+            return wordsH;
+        }
+
+        /// <summary>
+        /// 
+        /// </summary>
+        /// <param name="pageLetters">The letters in the page, they must have
+        /// the same text directions.</param>
+        /// <param name="metric">The letter's metric to use in the minimum distance
+        /// between 2 letters, e.g. GlyphRectangle.Width or GlyphRectangle.Height.</param>
+        /// <param name="distMeasure">The distance measure between two start and end base line points,
+        /// e.g. the Manhattan distance.</param>
+        /// <returns></returns>
+        private static List<Word> GetWords(IEnumerable<Letter> pageLetters,
+            Func<Letter, decimal> metric, Func<PdfPoint, PdfPoint, double> distMeasure)
+        {
+            if (pageLetters == null || pageLetters.Count() == 0) return new List<Word>();
+
+            if (pageLetters.Any(x => pageLetters.ElementAt(0).TextDirection != x.TextDirection))
+            {
+                throw new ArgumentException("NNWordExtractor.GetWords(): Mixed Text Direction.");
+            }
+
+            Letter[] letters = pageLetters.ToArray();
+            int lettersCount = letters.Length;
+            PdfPoint[] startBaseLines = letters.Select(x => x.StartBaseLine).ToArray();
+            int[] indexes = Enumerable.Repeat((int)-1, lettersCount).ToArray();
+
+            // Find nearest neighbours indexes
+            Parallel.For(0, lettersCount, c =>
+            {
+                var currentLetter = letters[c];
+                // only check neighbours if not a white space
+                if (!string.IsNullOrWhiteSpace(currentLetter.Value))
+                {
+                    int index = currentLetter.EndBaseLine.FindIndexNearest(startBaseLines, distMeasure, out double dist);
+                    var pairedLetter = letters[index];
+
+                    if (!string.IsNullOrWhiteSpace(pairedLetter.Value) &&
+                        string.Equals(currentLetter.FontName, pairedLetter.FontName, StringComparison.OrdinalIgnoreCase))
+                    {
+                        decimal minDist = Math.Max(Math.Abs(metric(currentLetter)), Math.Abs(metric(pairedLetter))) * 0.60m;
+                        if ((decimal)dist < minDist)
+                        {
+                            indexes[c] = index;
+                        }
+                    }
+                }
+            });
+
+            // Group indexes
+            List<List<int>> groupedIndexes = new List<List<int>>();
+            List<int> indexDone = new List<int>();
+            for (int c = 0; c < lettersCount; c++)
+            {
+                int i = indexes[c];
+                if (i == -1) continue;
+
+                bool isDoneC = indexDone.Contains(c);
+                bool isDoneI = indexDone.Contains(i);
+                if (isDoneC || isDoneI)
+                {
+                    if (isDoneC && !isDoneI)
+                    {
+                        foreach (var pair in groupedIndexes.Where(x => x.Contains(c)))
+                        {
+                            pair.Add(i);
+                        }
+                        indexDone.Add(i);
+                    }
+                    else if (!isDoneC && isDoneI)
+                    {
+                        foreach (var pair in groupedIndexes.Where(x => x.Contains(i)))
+                        {
+                            pair.Add(c);
+                        }
+                        indexDone.Add(c);
+                    }
+                    else
+                    {
+                        foreach (var pair in groupedIndexes.Where(x => x.Contains(i)))
+                        {
+                            if (!pair.Contains(c)) pair.Add(c);
+                        }
+
+                        foreach (var pair in groupedIndexes.Where(x => x.Contains(c)))
+                        {
+                            if (!pair.Contains(i)) pair.Add(i);
+                        }
+                    }
+                }
+                else
+                {
+                    List<int> pair = new List<int>() { c, i };
+                    groupedIndexes.Add(pair);
+                    indexDone.AddRange(pair);
+                }
+            }
+
+            // Merge lists with common index 
+            for (int c = 0; c < lettersCount; c++)
+            {
+                List<List<int>> candidates = groupedIndexes.Where(x => x.Any(t => t == c)).ToList();
+                if (candidates.Count < 2) continue; // only one group with this index
+
+                List<int> merged = candidates.First();
+                groupedIndexes.Remove(merged);
+                for (int i = 1; i < candidates.Count; i++)
+                {
+                    var current = candidates[i];
+                    merged = merged.Union(current).ToList();
+                    groupedIndexes.Remove(current);
+                }
+                groupedIndexes.Add(merged);
+            }
+
+            List<Word> words = new List<Word>();
+            for (int a = 0; a < groupedIndexes.Count(); a++)
+            {
+                List<Letter> groupedLetters = new List<Letter>();
+                foreach (int s in groupedIndexes[a])
+                {
+                    groupedLetters.Add(letters[s]);
+                }
+                words.Add(new Word(groupedLetters));
+            }
+
+            List<int> indexesNotDone = Enumerable.Range(0, lettersCount).Except(groupedIndexes.SelectMany(x => x)).ToList();
+            for (int n = 0; n < indexesNotDone.Count(); n++)
+            {
+                Letter letter = letters[indexesNotDone[n]];
+                words.Add(new Word(new Letter[] { letter }));
+            }
+
+            return words;
+        }
+    }
+}

src/UglyToad.PdfPig/DocumentLayoutAnalysis/RecursiveXYCut.cs

@@ -0,0 +1,411 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using UglyToad.PdfPig.Content;
+using UglyToad.PdfPig.Geometry;
+
+namespace UglyToad.PdfPig.DocumentLayoutAnalysis
+{
+    /// <summary>
+    /// The recursive X-Y cut is a top-down page segmentation technique that decomposes a document 
+    /// recursively into a set of rectangular blocks. This implementation leverages bounding boxes.
+    /// https://en.wikipedia.org/wiki/Recursive_X-Y_cut
+    /// <para>See 'Recursive X-Y Cut using Bounding Boxes of Connected Components' by Jaekyu Ha and Robert M.Haralick Ihsin T. Phillips</para>
+    /// </summary>
+    public class RecursiveXYCut
+    {
+        /// <summary>
+        /// Get the blocks.
+        /// </summary>
+        /// <param name="pageWords">The words in a page.</param>
+        /// <param name="minimumWidht">The minimum widht for a block.</param>
+        /// <param name="dominantFontWidth">The dominant font width.</param>
+        /// <param name="dominantFontHeight">The dominant font height.</param>
+        /// <returns></returns>
+        public static XYNode GetBlocks(IEnumerable<Word> pageWords, decimal minimumWidht,
+            decimal dominantFontWidth, decimal dominantFontHeight)
+        {
+            return GetBlocks(pageWords, minimumWidht, k => dominantFontWidth, k => dominantFontHeight);
+        }
+
+        /// <summary>
+        /// Get the blocks.
+        /// </summary>
+        /// <param name="pageWords">The words in a page.</param>
+        /// <param name="minimumWidht">The minimum widht for a block.</param>
+        /// <param name="dominantFontWidthFunc">The function that determines the dominant font width.</param>
+        /// <param name="dominantFontHeightFunc">The function that determines the dominant font height.</param>
+        /// <returns></returns>
+        public static XYNode GetBlocks(IEnumerable<Word> pageWords, decimal minimumWidht,
+            Func<IEnumerable<decimal>, decimal> dominantFontWidthFunc,
+            Func<IEnumerable<decimal>, decimal> dominantFontHeightFunc)
+        {
+            var root = new XYLeef(pageWords);
+            return VerticalCut(root, minimumWidht, dominantFontWidthFunc, dominantFontHeightFunc);
+        }
+
+        private static XYNode VerticalCut(XYLeef leef, decimal minimumWidht,
+            Func<IEnumerable<decimal>, decimal> dominantFontWidthFunc,
+            Func<IEnumerable<decimal>, decimal> dominantFontHeightFunc, int level = 0)
+        {
+            if (leef.CountWords() <= 1 || leef.BoundingBox.Width <= minimumWidht)
+            {
+                // we stop cutting if 
+                // - only one word remains
+                // - width is too small
+                return leef;
+            }
+
+            // order words left to right
+            var words = leef.Words.Where(w => !string.IsNullOrWhiteSpace(w.Text)).OrderBy(w => w.BoundingBox.Left).ToArray();
+
+            // determine dominantFontWidth and dominantFontHeight
+            decimal domFontWidth = dominantFontWidthFunc(words.SelectMany(x => x.Letters)
+                .Select(x => Math.Abs(x.GlyphRectangle.Width)));
+            decimal domFontHeight = dominantFontHeightFunc(words.SelectMany(x => x.Letters)
+                .Select(x => Math.Abs(x.GlyphRectangle.Height)));
+
+            List<decimal[]> projectionProfile = new List<decimal[]>();
+            decimal[] currentProj = new decimal[2] { words[0].BoundingBox.Left, words[0].BoundingBox.Right };
+            int wordsCount = words.Count();
+            for (int i = 1; i < wordsCount; i++)
+            {
+                if ((words[i].BoundingBox.Left >= currentProj[0] && words[i].BoundingBox.Left <= currentProj[1])
+                    || (words[i].BoundingBox.Right >= currentProj[0] && words[i].BoundingBox.Right <= currentProj[1]))
+                {
+                    // it is overlapping 
+                    if (words[i].BoundingBox.Left >= currentProj[0]
+                        && words[i].BoundingBox.Left <= currentProj[1]
+                        && words[i].BoundingBox.Right > currentProj[1])
+                    {
+                        // |____|
+                        //    |____|
+                        // |_______|    <- updated
+                        currentProj[1] = words[i].BoundingBox.Right;
+                    }
+
+                    // we ignore the following cases:
+                    //    |____|
+                    // |____|          (not possible because of OrderBy)
+                    // 
+                    //    |____|
+                    //|___________|    (not possible because of OrderBy)
+                    //
+                    //  |____|
+                    //   |_|
+                }
+                else
+                {
+                    // no overlap
+                    if (words[i].BoundingBox.Left - currentProj[1] <= domFontWidth)
+                    {
+                        // if gap too small -> don't cut
+                        // |____| |____|
+                        currentProj[1] = words[i].BoundingBox.Right;
+                    }
+                    else if (currentProj[1] - currentProj[0] < minimumWidht)
+                    {
+                        // still too small
+                        currentProj[1] = words[i].BoundingBox.Right;
+                    }
+                    else
+                    {
+                        // if gap big enough -> cut!
+                        // |____|   |   |____|
+                        if (i != wordsCount - 1) // will always add the last one after
+                        {
+                            projectionProfile.Add(currentProj);
+                            currentProj = new decimal[2] { words[i].BoundingBox.Left, words[i].BoundingBox.Right };
+                        }
+                    }
+                }
+                if (i == wordsCount - 1) projectionProfile.Add(currentProj);
+            }
+
+            var newLeefsEnums = projectionProfile.Select(p => leef.Words.Where(w => w.BoundingBox.Left >= p[0] && w.BoundingBox.Right <= p[1]));
+            var newLeefs = newLeefsEnums.Where(e => e.Count() > 0).Select(e => new XYLeef(e));
+
+            var newNodes = newLeefs.Select(l => HorizontalCut(l, minimumWidht,
+                dominantFontWidthFunc, dominantFontHeightFunc, level)).ToList();
+
+            var lost = leef.Words.Except(newLeefsEnums.SelectMany(x => x)).Where(x => !string.IsNullOrWhiteSpace(x.Text)).ToList();
+            if (lost.Count > 0)
+            {
+                newNodes.AddRange(lost.Select(w => new XYLeef(w)));
+            }
+
+            return new XYNode(newNodes);
+        }
+
+        private static XYNode HorizontalCut(XYLeef leef, decimal minimumWidht,
+            Func<IEnumerable<decimal>, decimal> dominantFontWidthFunc,
+            Func<IEnumerable<decimal>, decimal> dominantFontHeightFunc, int level = 0)
+        {
+            if (leef.CountWords() <= 1)
+            {
+                // we stop cutting if 
+                // - only one word remains
+                return leef;
+            }
+
+            var words = leef.Words.Where(w => !string.IsNullOrWhiteSpace(w.Text)).OrderBy(w => w.BoundingBox.Bottom).ToArray(); // order bottom to top
+
+            // determine dominantFontWidth and dominantFontHeight
+            decimal domFontWidth = dominantFontWidthFunc(words.SelectMany(x => x.Letters)
+                .Select(x => Math.Abs(x.GlyphRectangle.Width)));
+            decimal domFontHeight = dominantFontHeightFunc(words.SelectMany(x => x.Letters)
+                .Select(x => Math.Abs(x.GlyphRectangle.Height)));
+
+            List<decimal[]> projectionProfile = new List<decimal[]>();
+            decimal[] currentProj = new decimal[2] { words[0].BoundingBox.Bottom, words[0].BoundingBox.Top };
+            int wordsCount = words.Count();
+            for (int i = 1; i < wordsCount; i++)
+            {
+                if ((words[i].BoundingBox.Bottom >= currentProj[0] && words[i].BoundingBox.Bottom <= currentProj[1])
+                    || (words[i].BoundingBox.Top >= currentProj[0] && words[i].BoundingBox.Top <= currentProj[1]))
+                {
+                    // it is overlapping 
+                    if (words[i].BoundingBox.Bottom >= currentProj[0]
+                        && words[i].BoundingBox.Bottom <= currentProj[1]
+                        && words[i].BoundingBox.Top > currentProj[1])
+                    {
+                        currentProj[1] = words[i].BoundingBox.Top;
+                    }
+                }
+                else
+                {
+                    // no overlap
+                    if (words[i].BoundingBox.Bottom - currentProj[1] <= domFontHeight)
+                    {
+                        // if gap too small -> don't cut
+                        // |____| |____|
+                        currentProj[1] = words[i].BoundingBox.Top;
+                    }
+                    else
+                    {
+                        // if gap big enough -> cut!
+                        // |____|   |   |____|
+                        if (i != wordsCount - 1) // will always add the last one after
+                        {
+                            projectionProfile.Add(currentProj);
+                            currentProj = new decimal[2] { words[i].BoundingBox.Bottom, words[i].BoundingBox.Top };
+                        }
+                    }
+                }
+                if (i == wordsCount - 1) projectionProfile.Add(currentProj);
+            }
+
+            if (projectionProfile.Count == 1)
+            {
+                if (level >= 1)
+                {
+                    return leef;
+                }
+                else
+                {
+                    level++;
+                }
+            }
+
+            var newLeefsEnums = projectionProfile.Select(p =>
+                leef.Words.Where(w => w.BoundingBox.Bottom >= p[0] && w.BoundingBox.Top <= p[1]));
+            var newLeefs = newLeefsEnums.Where(e => e.Count() > 0).Select(e => new XYLeef(e));
+            var newNodes = newLeefs.Select(l => VerticalCut(l, minimumWidht,
+                dominantFontWidthFunc, dominantFontHeightFunc, level)).ToList();
+
+            var lost = leef.Words.Except(newLeefsEnums.SelectMany(x => x)).Where(x => !string.IsNullOrWhiteSpace(x.Text)).ToList();
+            if (lost.Count > 0)
+            {
+                newNodes.AddRange(lost.Select(w => new XYLeef(w)));
+            }
+            return new XYNode(newNodes);
+        }
+    }
+
+    /// <summary>
+    /// A Node used in the <see cref="RecursiveXYCut"/> algorithm.
+    /// </summary>
+    public class XYNode
+    {
+        /// <summary>
+        /// Returns true if this node is a leef, false otherwise.
+        /// </summary>
+        public virtual bool IsLeef => false;
+
+        /// <summary>
+        /// The rectangle completely containing the node.
+        /// </summary>
+        public PdfRectangle BoundingBox { get; set; }
+
+        /// <summary>
+        /// The children of the node.
+        /// </summary>
+        public XYNode[] Children { get; set; }
+
+        /// <summary>
+        /// Recursively counts the words included in this node.
+        /// </summary>
+        /// <returns></returns>
+        public virtual int CountWords()
+        {
+            if (Children == null) return 0;
+            int count = 0;
+            RecursiveCount(Children, ref count);
+            return count;
+        }
+
+        /// <summary>
+        /// Recursively gets the leefs (last nodes) of this node.
+        /// </summary>
+        /// <returns></returns>
+        public virtual List<XYLeef> GetLeefs()
+        {
+            List<XYLeef> leefs = new List<XYLeef>();
+            if (Children == null || Children.Count() == 0) return leefs;
+            int level = 0;
+            RecursiveGetLeefs(Children, ref leefs, level);
+            return leefs;
+        }
+
+        /// <summary>
+        /// Create a new <see cref="XYNode"/>.
+        /// </summary>
+        /// <param name="children"></param>
+        public XYNode(params XYNode[] children)
+            : this(children?.ToList())
+        {
+
+        }
+
+        /// <summary>
+        /// Create a new <see cref="XYNode"/>.
+        /// </summary>
+        /// <param name="children"></param>
+        public XYNode(IEnumerable<XYNode> children)
+        {
+            if (children != null && children.Count() != 0)
+            {
+                Children = children.ToArray();
+                decimal left = children.Min(b => b.BoundingBox.Left);
+                decimal right = children.Max(b => b.BoundingBox.Right);
+                decimal bottom = children.Min(b => b.BoundingBox.Bottom);
+                decimal top = children.Max(b => b.BoundingBox.Top);
+                BoundingBox = new PdfRectangle(left, bottom, right, top);
+            }
+        }
+
+        private void RecursiveCount(IEnumerable<XYNode> children, ref int count)
+        {
+            if (children.Count() == 0) return;
+            foreach (XYNode node in children.Where(x => x.IsLeef))
+            {
+                count += node.CountWords();
+            }
+
+            foreach (XYNode node in children.Where(x => !x.IsLeef))
+            {
+                RecursiveCount(node.Children, ref count);
+            }
+        }
+
+        private void RecursiveGetLeefs(IEnumerable<XYNode> children, ref List<XYLeef> leefs, int level)
+        {
+            if (children.Count() == 0) return;
+            bool isVerticalCut = level % 2 == 0;
+
+            foreach (XYLeef node in children.Where(x => x.IsLeef))
+            {
+                leefs.Add(node);
+            }
+
+            level++;
+
+            IEnumerable<XYNode> notLeefs = children.Where(x => !x.IsLeef);
+
+            if (isVerticalCut)
+            {
+                notLeefs = notLeefs.OrderBy(x => x.BoundingBox.Left).ToList();
+            }
+            else
+            {
+                notLeefs = notLeefs.OrderByDescending(x => x.BoundingBox.Top).ToList();
+            }
+
+            foreach (XYNode node in notLeefs)
+            {
+                RecursiveGetLeefs(node.Children, ref leefs, level);
+            }
+        }
+
+        public override string ToString()
+        {
+            return (IsLeef ? "Leef" : "Node");
+        }
+    }
+
+    /// <summary>
+    /// A Leef node used in the <see cref="RecursiveXYCut"/> algorithm, i.e. a block.
+    /// </summary>
+    public class XYLeef : XYNode
+    {
+        /// <summary>
+        /// Returns true if this node is a leef, false otherwise.
+        /// </summary>
+        public override bool IsLeef => true;
+
+        /// <summary>
+        /// The words in the leef.
+        /// </summary>
+        public Word[] Words { get; set; }
+
+        /// <summary>
+        /// The number of words in the leef.
+        /// </summary>
+        /// <returns></returns>
+        public override int CountWords() => Words == null ? 0 : Words.Length;
+
+        /// <summary>
+        /// Returns null as a leef doesn't have leefs.
+        /// </summary>
+        /// <returns></returns>
+        public override List<XYLeef> GetLeefs()
+        {
+            return null;
+        }
+
+        /// <summary>
+        /// Gets the lines of the leef.
+        /// </summary>
+        /// <returns></returns>
+        public TextLine[] GetLines()
+        {
+            var groupedWords = Words.GroupBy(x => x.BoundingBox.Bottom).ToDictionary(x => x.Key, x => x.ToList());
+            return groupedWords.OrderByDescending(x => x.Key).Select(ws => new TextLine(ws.Value)).ToArray();
+        }
+
+        /// <summary>
+        /// Create a new <see cref="XYLeef"/>.
+        /// </summary>
+        /// <param name="words">The words contained in the leef.</param>
+        public XYLeef(params Word[] words) : this(words == null ? null : words.ToList())
+        {
+
+        }
+
+        /// <summary>
+        /// Create a new <see cref="XYLeef"/>.
+        /// </summary>
+        /// <param name="words">The words contained in the leef.</param>
+        public XYLeef(IEnumerable<Word> words) : base(null)
+        {
+            decimal left = words.Min(b => b.BoundingBox.Left);
+            decimal right = words.Max(b => b.BoundingBox.Right);
+
+            decimal bottom = words.Min(b => b.BoundingBox.Bottom);
+            decimal top = words.Max(b => b.BoundingBox.Top);
+
+            BoundingBox = new PdfRectangle(left, bottom, right, top);
+            Words = words.ToArray();
+        }
+    }
+}