提取为

Artikelnr. Omschrijving Aantal
Per stuk Kosten
VERHUUR L. GELEVERDE ARBEID PDC 8 € 43,70 € 349,60
VERHUUR O. GELEVERDE ARBEID PDC 3 € 60,95 € 182,85
VERHUUR L.L. GELEVERDE ARBEID EM 24
€ 32,20 € 772,80

首先，为什么会发生

正如对该问题的评论所猜想的那样，确实存在一个小的垂直步骤，在所有行中，前三列均设置为相同的垂直位置，而后两列的垂直位置略有不同，

    Row       First columns y   Last columns y
Heading row               536          535.893
First row                 516          516.229
Second row                495          495.478
Third row                 475          474.788

人们特别认识到，由文本提取破坏的行是其中y位置的小数点前数字不同（536与535、475与474）的行，而那些具有相同的小数点位数不变的行。

这样做的原因是该类TextChunkLocationDefaultImp（默认情况下用于存储文本块位置和用于比较这些位置的方法）以整数形式存储块的y位置（实际上，它的抽象也适用于未水平书写的文本）变量（private readonly int distPerpendicular）并在测试方法中SameLine要求distPerpendicular值相等。

namespace iText.Kernel.Pdf.Canvas.Parser.Listener {
    internal class TextChunkLocationDefaultImp : ITextChunkLocation {
        ...
        /// <summary>Perpendicular distance to the orientation unit vector (i.e. the Y position in an unrotated coordinate system).
        ///     </summary>
        /// <remarks>
        /// Perpendicular distance to the orientation unit vector (i.e. the Y position in an unrotated coordinate system).
        /// We round to the nearest integer to handle the fuzziness of comparing floats.
        /// </remarks>
        private readonly int distPerpendicular;
        ...
        /// <param name="as">the location to compare to</param>
        /// <returns>true is this location is on the the same line as the other</returns>
        public virtual bool SameLine(ITextChunkLocation @as) {
            ...
            float distPerpendicularDiff = DistPerpendicular() - @as.DistPerpendicular();
            if (distPerpendicularDiff == 0) {
                return true;
            }
            ...
        }
        ...
    }
}

（实际上，SameLine如果所比较的文本块之一的长度为零，则向下进一步允许小偏差。显然，零长度的块有时用于变音标记，而这些标记有时应用于不同的高度。在您的示例中，这无关紧要文件）。

如何修复

如上所述，问题是由于的行为引起的TextChunkLocationDefaultImp.SameLine。因此，我们必须改变这种行为。但是，通常，我们通常不想更改iText类本身的代码。

幸运的是，它LocationTextExtractionStrategy具有一个允许注入ITextChunkLocationStrategy实现的构造函数，即ITextChunkLocation实例的工厂对象。

因此，对于我们的任务，我们必须编写一个ITextChunkLocation不太严格的替代实现，以及一个ITextChunkLocationStrategy生成我们ITextChunkLocation实现实例的实现。

不幸的是，虽然TextChunkLocationDefaultImp是internal对的iText和拥有众多的私有变量。因此，我们不能简单地从中获取实现，而必须将其整体复制并粘贴并将更改应用于该副本。

从而，

class LaxTextChunkLocationStrategy : LocationTextExtractionStrategy.ITextChunkLocationStrategy
{
    public LaxTextChunkLocationStrategy()
    {
    }

    public virtual ITextChunkLocation CreateLocation(TextRenderInfo renderInfo, LineSegment baseline)
    {
        return new TextChunkLocationLaxImp(baseline.GetStartPoint(), baseline.GetEndPoint(), renderInfo.GetSingleSpaceWidth());
    }
}

class TextChunkLocationLaxImp : ITextChunkLocation
{
    private const float DIACRITICAL_MARKS_ALLOWED_VERTICAL_DEVIATION = 2;
    private readonly Vector startLocation;
    private readonly Vector endLocation;
    private readonly Vector orientationVector;
    private readonly int orientationMagnitude;
    private readonly int distPerpendicular;
    private readonly float distParallelStart;
    private readonly float distParallelEnd;
    private readonly float charSpaceWidth;

    public TextChunkLocationLaxImp(Vector startLocation, Vector endLocation, float charSpaceWidth)
    {
        this.startLocation = startLocation;
        this.endLocation = endLocation;
        this.charSpaceWidth = charSpaceWidth;
        Vector oVector = endLocation.Subtract(startLocation);
        if (oVector.Length() == 0)
        {
            oVector = new Vector(1, 0, 0);
        }
        orientationVector = oVector.Normalize();
        orientationMagnitude = (int)(Math.Atan2(orientationVector.Get(Vector.I2), orientationVector.Get(Vector.I1)) * 1000);
        Vector origin = new Vector(0, 0, 1);
        distPerpendicular = (int)(startLocation.Subtract(origin)).Cross(orientationVector).Get(Vector.I3);
        distParallelStart = orientationVector.Dot(startLocation);
        distParallelEnd = orientationVector.Dot(endLocation);
    }

    public virtual int OrientationMagnitude()
    {
        return orientationMagnitude;
    }

    public virtual int DistPerpendicular()
    {
        return distPerpendicular;
    }

    public virtual float DistParallelStart()
    {
        return distParallelStart;
    }

    public virtual float DistParallelEnd()
    {
        return distParallelEnd;
    }

    public virtual Vector GetStartLocation()
    {
        return startLocation;
    }

    public virtual Vector GetEndLocation()
    {
        return endLocation;
    }

    public virtual float GetCharSpaceWidth()
    {
        return charSpaceWidth;
    }

    public virtual bool SameLine(ITextChunkLocation @as)
    {
        if (OrientationMagnitude() != @as.OrientationMagnitude())
        {
            return false;
        }
        int distPerpendicularDiff = DistPerpendicular() - @as.DistPerpendicular();
        if (Math.Abs(distPerpendicularDiff) < 2)
        {
            return true;
        }
        LineSegment mySegment = new LineSegment(startLocation, endLocation);
        LineSegment otherSegment = new LineSegment(@as.GetStartLocation(), @as.GetEndLocation());
        return Math.Abs(distPerpendicularDiff) <= DIACRITICAL_MARKS_ALLOWED_VERTICAL_DEVIATION && (mySegment.GetLength() == 0 || otherSegment.GetLength() == 0);
    }

    public virtual float DistanceFromEndOf(ITextChunkLocation other)
    {
        return DistParallelStart() - other.DistParallelEnd();
    }

    public virtual bool IsAtWordBoundary(ITextChunkLocation previous)
    {
        if (startLocation.Equals(endLocation) || previous.GetEndLocation().Equals(previous.GetStartLocation()))
        {
            return false;
        }
        float dist = DistanceFromEndOf(previous);
        if (dist < 0)
        {
            dist = previous.DistanceFromEndOf(this);
            //The situation when the chunks intersect. We don't need to add space in this case
            if (dist < 0)
            {
                return false;
            }
        }
        return dist > GetCharSpaceWidth() / 2.0f;
    }

    internal static bool ContainsMark(ITextChunkLocation baseLocation, ITextChunkLocation markLocation)
    {
        return baseLocation.GetStartLocation().Get(Vector.I1) <= markLocation.GetStartLocation().Get(Vector.I1) &&
             baseLocation.GetEndLocation().Get(Vector.I1) >= markLocation.GetEndLocation().Get(Vector.I1) && Math.
            Abs(baseLocation.DistPerpendicular() - markLocation.DistPerpendicular()) <= DIACRITICAL_MARKS_ALLOWED_VERTICAL_DEVIATION;
    }
}

现在，让您的代码使用这些类，替换

string output = PdfTextExtractor.GetTextFromPage(pdfDoc.GetPage(i));

通过

LocationTextExtractionStrategy laxStrategy = new LocationTextExtractionStrategy(new LaxTextChunkLocationStrategy());
string output = PdfTextExtractor.GetTextFromPage(pdfDoc.GetPage(i), laxStrategy);

文本提取结果变为

Artikelnr. Omschrijving Aantal Per stuk Kosten
VERHUUR L. GELEVERDE ARBEID PDC 8 € 43,70 € 349,60
VERHUUR O. GELEVERDE ARBEID PDC 3 € 60,95 € 182,85
VERHUUR L.L. GELEVERDE ARBEID EM 24 € 32,20 € 772,80

如所期望的。

其他问题

如何检查pdf以了解行的确切位置

在您询问的评论中

请问您如何通过pdf知道行的确切位置？

我使用iText RUPS检查了页面：

在屏幕截图中选择的流的内容中，我发现：

q
...
q
1 0 0 1 60 536 cm
BT
8 0 0 8 0 0 Tm
/F3 1 Tf
(Artikelnr) Tj
8 0 0 8 31.84 0 Tm
(.) Tj
ET
Q
Q
q
...
q
1 0 0 1 147 536 cm
BT
8 0 0 8 0 0 Tm
/F3 1 Tf
(Omschrijving) Tj
ET
Q
Q
q
...
q
1 0 0 1 370 536 cm
BT
8 0 0 8 0 0 Tm
/F3 1 Tf
(Aantal) Tj
ET
Q
Q
q
...
q
1 0 0 1 433.404 535.893 cm
BT
8 0 0 8 0 0 Tm
/F3 1 Tf
(Per stuk) Tj
ET
Q
Q
q
...
q
1 0 0 1 504.878 535.893 cm
BT
8 0 0 8 0 0 Tm
/F3 1 Tf
(Kosten) Tj
ET
Q
Q 

您会看到前三个标题之前

1 0 0 1 XXX 536 cm

在最后两个标题之前

1 0 0 1 XXX 535.893 cm

由于文本矩阵始终设置8 0 0 8 XXX 0 Tm为沿y轴没有平移部分，因此上述cm指令设置了坐标系，以便分别在y位置536或535.893绘制文本。