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add ReadingOrderHelper

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BobLd
2020-05-23 20:03:18 +01:00
committed by Eliot Jones
parent ec613d337f
commit 79b78f486a
1 changed files with 163 additions and 0 deletions
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src/UglyToad.PdfPig.DocumentLayoutAnalysis/ReadingOrderDetector/ReadingOrderHelper.cs Normal file
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namespace UglyToad.PdfPig.DocumentLayoutAnalysis.ReadingOrderDetector
{
using System;
using System.Collections.Generic;
using System.Linq;
using UglyToad.PdfPig.Content;
/// <summary>
/// Helper functions for words and lines ordering.
/// </summary>
public static class ReadingOrderHelper
{
/// <summary>
/// Order words by reading order in a line.
/// <para>Assumes LtR and accounts for rotation.</para>
/// </summary>
/// <param name="words"></param>
public static List<Word> OrderByReadingOrder(this IEnumerable<Word> words)
{
if (words.Count() <= 1)
{
return words.ToList();
}
var TextOrientation = words.First().TextOrientation;
if (TextOrientation != TextOrientation.Other)
{
foreach (var word in words)
{
if (word.TextOrientation != TextOrientation)
{
TextOrientation = TextOrientation.Other;
break;
}
}
}
switch (TextOrientation)
{
case TextOrientation.Horizontal:
return words.OrderBy(w => w.BoundingBox.BottomLeft.X).ToList();
case TextOrientation.Rotate180:
return words.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ToList();
case TextOrientation.Rotate90:
return words.OrderByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
case TextOrientation.Rotate270:
return words.OrderBy(w => w.BoundingBox.BottomLeft.Y).ToList();
case TextOrientation.Other:
default:
// We consider the words roughly have the same rotation.
var avgAngle = words.Average(w => w.BoundingBox.Rotation);
if (double.IsNaN(avgAngle))
{
throw new NotFiniteNumberException("OrderByReadingOrder: NaN bounding box rotation found when ordering words.", avgAngle);
}
if (0 < avgAngle && avgAngle <= 90)
{
// quadrant 1, 0 < θ < π/2
return words.OrderBy(w => w.BoundingBox.BottomLeft.X).ThenBy(w => w.BoundingBox.BottomLeft.Y).ToList();
}
else if (90 < avgAngle && avgAngle <= 180)
{
// quadrant 2, π/2 < θ ≤ π
return words.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ThenBy(w => w.BoundingBox.BottomLeft.Y).ToList();
}
else if (-180 < avgAngle && avgAngle <= -90)
{
// quadrant 3, -π < θ < -π/2
return words.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ThenByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
}
else if (-90 < avgAngle && avgAngle <= 0)
{
// quadrant 4, -π/2 < θ < 0
return words.OrderBy(w => w.BoundingBox.BottomLeft.X).ThenByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
}
else
{
throw new ArgumentException("OrderByReadingOrder: unknown bounding box rotation found when ordering words.", nameof(avgAngle));
}
}
}
/// <summary>
/// Order lines by reading order in a block.
/// <para>Assumes TtB and accounts for rotation.</para>
/// </summary>
/// <param name="lines"></param>
public static IReadOnlyList<TextLine> OrderByReadingOrder(this IEnumerable<TextLine> lines)
{
if (lines.Count() <= 1)
{
return lines.ToList();
}
var TextOrientation = lines.First().TextOrientation;
if (TextOrientation != TextOrientation.Other)
{
foreach (var line in lines)
{
if (line.TextOrientation != TextOrientation)
{
TextOrientation = TextOrientation.Other;
break;
}
}
}
switch (TextOrientation)
{
case TextOrientation.Horizontal:
return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
case TextOrientation.Rotate180:
return lines.OrderBy(w => w.BoundingBox.BottomLeft.Y).ToList();
case TextOrientation.Rotate90:
return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ToList();
case TextOrientation.Rotate270:
return lines.OrderBy(w => w.BoundingBox.BottomLeft.X).ToList();
case TextOrientation.Other:
default:
// We consider the lines roughly have the same rotation.
var avgAngle = lines.Average(w => w.BoundingBox.Rotation);
if (double.IsNaN(avgAngle))
{
throw new NotFiniteNumberException("OrderByReadingOrder: NaN bounding box rotation found when ordering lines.", avgAngle);
}
if (0 < avgAngle && avgAngle <= 90)
{
// quadrant 1, 0 < θ < π/2
return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.Y).ThenBy(w => w.BoundingBox.BottomLeft.X).ToList();
}
else if (90 < avgAngle && avgAngle <= 180)
{
// quadrant 2, π/2 < θ ≤ π
return lines.OrderBy(w => w.BoundingBox.BottomLeft.X).ThenBy(w => w.BoundingBox.BottomLeft.Y).ToList();
}
else if (-180 < avgAngle && avgAngle <= -90)
{
// quadrant 3, -π < θ < -π/2
return lines.OrderBy(w => w.BoundingBox.BottomLeft.Y).ThenByDescending(w => w.BoundingBox.BottomLeft.X).ToList();
}
else if (-90 < avgAngle && avgAngle <= 0)
{
// quadrant 4, -π/2 < θ < 0
return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ThenByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
}
else
{
throw new ArgumentException("OrderByReadingOrder: unknown bounding box rotation found when ordering lines.", nameof(avgAngle));
}
}
}
}
}