Document Layout Analysis - Text edges extractor

src/UglyToad.PdfPig.Tests/PublicApiScannerTests.cs

@@ -65,6 +65,7 @@ public void OnlyExposedApiIsPublic()
                 "UglyToad.PdfPig.DocumentLayoutAnalysis.RecursiveXYCut",
                 "UglyToad.PdfPig.DocumentLayoutAnalysis.XYNode",
                 "UglyToad.PdfPig.DocumentLayoutAnalysis.XYLeaf",
+                "UglyToad.PdfPig.DocumentLayoutAnalysis.TextEdgesExtractor",
                 "UglyToad.PdfPig.Exceptions.PdfDocumentEncryptedException",
                 "UglyToad.PdfPig.Exceptions.PdfDocumentFormatException",
                 "UglyToad.PdfPig.Fonts.DescriptorFontFile",

src/UglyToad.PdfPig/DocumentLayoutAnalysis/TextEdgesExtractor.cs

@@ -0,0 +1,83 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using UglyToad.PdfPig.Content;
+using UglyToad.PdfPig.Geometry;
+
+namespace UglyToad.PdfPig.DocumentLayoutAnalysis
+{
+    /// <summary>
+    /// Text edges extractor. Text edges are where words have either there BoundingBox's left, right or mid coordinates aligned on the same vertical line.
+    /// <para>Useful to detect text columns, tables, justified text, lists, etc.</para>
+    /// </summary>
+    public class TextEdgesExtractor
+    {
+        /// <summary>
+        /// Functions used to define left, middle and right edges.
+        /// </summary>
+        private static readonly Tuple<string, Func<PdfRectangle, decimal>>[] edgesFuncs = new Tuple<string, Func<PdfRectangle, decimal>>[]
+        {
+            Tuple.Create<string, Func<PdfRectangle, decimal>>("left",   x => Math.Round(x.Left, 0)),                // use BoundingBox's left coordinate
+            Tuple.Create<string, Func<PdfRectangle, decimal>>("mid", x => Math.Round(x.Left + x.Width / 2, 0)),     // use BoundingBox's mid coordinate
+            Tuple.Create<string, Func<PdfRectangle, decimal>>("right",  x => Math.Round(x.Right, 0))                // use BoundingBox's right coordinate
+        };
+
+        /// <summary>
+        /// Get the text edges.
+        /// </summary>
+        /// <param name="pageWords">The words in the page.</param>
+        /// <param name="minimumElements">The minimum number of elements to define a text edge.</param>
+        public static Dictionary<string, List<PdfLine>> GetEdges(IEnumerable<Word> pageWords, int minimumElements = 4)
+        {
+            var cleanWords = pageWords.Where(x => !string.IsNullOrWhiteSpace(x.Text.Trim()));
+
+            ConcurrentDictionary<string, List<PdfLine>> dictionary = new ConcurrentDictionary<string, List<PdfLine>>();
+
+            Parallel.ForEach(edgesFuncs, f =>
+            {
+                dictionary.TryAdd(f.Item1, GetVerticalEdges(cleanWords, f.Item2, minimumElements));
+            });
+            return dictionary.ToDictionary(x => x.Key, x => x.Value);
+        }
+
+        private static List<PdfLine> GetVerticalEdges(IEnumerable<Word> pageWords, Func<PdfRectangle, decimal> func, int minimumElements)
+        {
+            Dictionary<decimal, List<Word>> edges = pageWords.GroupBy(x => func(x.BoundingBox))
+                .Where(x => x.Count() >= minimumElements).ToDictionary(gdc => gdc.Key, gdc => gdc.ToList());
+            Dictionary<decimal, List<List<Word>>> cleanEdges = new Dictionary<decimal, List<List<Word>>>();
+
+            foreach (var edge in edges)
+            {
+                var sortedEdges = edge.Value.OrderBy(x => x.BoundingBox.Bottom).ToList();
+                cleanEdges.Add(edge.Key, new List<List<Word>>());
+
+                var cuttings = pageWords.Except(edge.Value) // remove selected words
+                    // words that cut the vertical line
+                    .Where(x => x.BoundingBox.Left < edge.Key && x.BoundingBox.Right > edge.Key)
+                    // and that are within the boundaries of the edge
+                    .Where(k => k.BoundingBox.Bottom > edge.Value.Min(z => z.BoundingBox.Bottom)
+                        && k.BoundingBox.Top < edge.Value.Max(z => z.BoundingBox.Top))
+                    .OrderBy(x => x.BoundingBox.Bottom).ToList();
+
+                if (cuttings.Count > 0)
+                {
+                    foreach (var cut in cuttings)
+                    {
+                        var group1 = sortedEdges.Where(x => x.BoundingBox.Top < cut.BoundingBox.Bottom).ToList();
+                        if (group1.Count >= minimumElements) cleanEdges[edge.Key].Add(group1);
+                        sortedEdges = sortedEdges.Except(group1).ToList();
+                    }
+                    if (sortedEdges.Count >= minimumElements) cleanEdges[edge.Key].Add(sortedEdges);
+                }
+                else
+                {
+                    cleanEdges[edge.Key].Add(sortedEdges);
+                }
+            }
+
+            return cleanEdges.SelectMany(x => x.Value.Select(y => new PdfLine(x.Key, y.Min(w => w.BoundingBox.Bottom), x.Key, y.Max(w => w.BoundingBox.Top)))).ToList();
+        }
+    }
+}