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How can I extract index / superscript from a PDF using iTextSharp?

iTextSharp works well, it extracts plain text from PDF documents, but I am having problems with index / superscript text common in technical documents.

TextChunk.SameLine()requires that two pieces have the same vertical positioning as "on" on the same line, which does not apply to superscript or subscript text. For example, on page 11 of this document in the section "COMBUSTION EFFICIENCY":

http://www.mass.gov/courts/docs/lawlib/300-399cmr/310cmr7.pdf

Expected Text:

monoxide (CO) in flue gas in accordance with the following formula: C.E. = [CO2 /(CO + CO2)]

Result text:

monoxide (CO) in flue gas in accordance with the following formula: C.E. = [CO /(CO + CO )] 
2 2

SameLine() LocationTextExtractionStrategy TextChunk, . " " , :

public class SubSuperStrategy : LocationTextExtractionStrategy {
  public int SameLineOrientationTolerance { get; set; }
  public int SameLineDistanceTolerance { get; set; }

  public override bool SameLine(TextChunk chunk1, TextChunk chunk2) {
    var orientationDelta = Math.Abs(chunk1.OrientationMagnitude
       - chunk2.OrientationMagnitude);
    if(orientationDelta > SameLineOrientationTolerance) return false;
    var distDelta = Math.Abs(chunk1.DistPerpendicular
       - chunk2.DistPerpendicular);
    return (distDelta <= SameLineDistanceTolerance);
    }
}

SameLineDistanceTolerance of 3, , /, :

monoxide (CO) in flue gas in accordance with the following formula:   C.E. = [CO /(CO + CO )] 2 2

- , ( ) . , . , - , .

- ?

( , .)

+4
2

, , , . .

Java/iText; , Java #/iTextSharp.

Java iText

iText 5.5.8-SNAPSHOT.

, , RenderListener :

public class TextLineFinder implements RenderListener
{
    @Override
    public void beginTextBlock() { }
    @Override
    public void endTextBlock() { }
    @Override
    public void renderImage(ImageRenderInfo renderInfo) { }

    /*
     * @see RenderListener#renderText(TextRenderInfo)
     */
    @Override
    public void renderText(TextRenderInfo renderInfo)
    {
        LineSegment ascentLine = renderInfo.getAscentLine();
        LineSegment descentLine = renderInfo.getDescentLine();
        float[] yCoords = new float[]{
                ascentLine.getStartPoint().get(Vector.I2),
                ascentLine.getEndPoint().get(Vector.I2),
                descentLine.getStartPoint().get(Vector.I2),
                descentLine.getEndPoint().get(Vector.I2)
        };
        Arrays.sort(yCoords);
        addVerticalUseSection(yCoords[0], yCoords[3]);
    }

    /**
     * This method marks the given interval as used.
     */
    void addVerticalUseSection(float from, float to)
    {
        if (to < from)
        {
            float temp = to;
            to = from;
            from = temp;
        }

        int i=0, j=0;
        for (; i<verticalFlips.size(); i++)
        {
            float flip = verticalFlips.get(i);
            if (flip < from)
                continue;

            for (j=i; j<verticalFlips.size(); j++)
            {
                flip = verticalFlips.get(j);
                if (flip < to)
                    continue;
                break;
            }
            break;
        }
        boolean fromOutsideInterval = i%2==0;
        boolean toOutsideInterval = j%2==0;

        while (j-- > i)
            verticalFlips.remove(j);
        if (toOutsideInterval)
            verticalFlips.add(i, to);
        if (fromOutsideInterval)
            verticalFlips.add(i, from);
    }

    final List<Float> verticalFlips = new ArrayList<Float>();
}

(TextLineFinder.java)

RenderListener , y. , , .

PageVerticalAnalyzer, .

, , iText LocationTextExtractionStrategy :

public class HorizontalTextExtractionStrategy extends LocationTextExtractionStrategy
{
    public class HorizontalTextChunk extends TextChunk
    {
        public HorizontalTextChunk(String string, Vector startLocation, Vector endLocation, float charSpaceWidth)
        {
            super(string, startLocation, endLocation, charSpaceWidth);
        }

        @Override
        public int compareTo(TextChunk rhs)
        {
            if (rhs instanceof HorizontalTextChunk)
            {
                HorizontalTextChunk horRhs = (HorizontalTextChunk) rhs;
                int rslt = Integer.compare(getLineNumber(), horRhs.getLineNumber());
                if (rslt != 0) return rslt;
                return Float.compare(getStartLocation().get(Vector.I1), rhs.getStartLocation().get(Vector.I1));
            }
            else
                return super.compareTo(rhs);
        }

        @Override
        public boolean sameLine(TextChunk as)
        {
            if (as instanceof HorizontalTextChunk)
            {
                HorizontalTextChunk horAs = (HorizontalTextChunk) as;
                return getLineNumber() == horAs.getLineNumber();
            }
            else
                return super.sameLine(as);
        }

        public int getLineNumber()
        {
            Vector startLocation = getStartLocation();
            float y = startLocation.get(Vector.I2);
            List<Float> flips = textLineFinder.verticalFlips;
            if (flips == null || flips.isEmpty())
                return 0;
            if (y < flips.get(0))
                return flips.size() / 2 + 1;
            for (int i = 1; i < flips.size(); i+=2)
            {
                if (y < flips.get(i))
                {
                    return (1 + flips.size() - i) / 2;
                }
            }
            return 0;
        }
    }

    @Override
    public void renderText(TextRenderInfo renderInfo)
    {
        textLineFinder.renderText(renderInfo);

        LineSegment segment = renderInfo.getBaseline();
        if (renderInfo.getRise() != 0){ // remove the rise from the baseline - we do this because the text from a super/subscript render operations should probably be considered as part of the baseline of the text the super/sub is relative to 
            Matrix riseOffsetTransform = new Matrix(0, -renderInfo.getRise());
            segment = segment.transformBy(riseOffsetTransform);
        }
        TextChunk location = new HorizontalTextChunk(renderInfo.getText(), segment.getStartPoint(), segment.getEndPoint(), renderInfo.getSingleSpaceWidth());
        getLocationalResult().add(location);        
    }

    public HorizontalTextExtractionStrategy() throws NoSuchFieldException, SecurityException
    {
        locationalResultField = LocationTextExtractionStrategy.class.getDeclaredField("locationalResult");
        locationalResultField.setAccessible(true);

        textLineFinder = new TextLineFinder();
    }

    @SuppressWarnings("unchecked")
    List<TextChunk> getLocationalResult()
    {
        try
        {
            return (List<TextChunk>) locationalResultField.get(this);
        }
        catch (IllegalArgumentException | IllegalAccessException e)
        {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }

    final Field locationalResultField;
    final TextLineFinder textLineFinder;
}

(HorizontalTextExtractionStrategy.java)

TextExtractionStrategy TextLineFinder , .

. . . LocationTextExtractionStrategy .

, :

String extract(PdfReader reader, int pageNo) throws IOException, NoSuchFieldException, SecurityException
{
    return PdfTextExtractor.getTextFromPage(reader, pageNo, new HorizontalTextExtractionStrategy());
}

( ExtractSuperAndSubInLine.java)

. 11 OP " " :

monoxide (CO) in flue gas in accordance with the following formula:   C.E. = [CO 2/(CO + CO 2 )]

# iTextSharp

, , Java, , :

iTextSharp 5.5.7.

public class TextLineFinder : IRenderListener
{
    public void BeginTextBlock() { }
    public void EndTextBlock() { }
    public void RenderImage(ImageRenderInfo renderInfo) { }

    public void RenderText(TextRenderInfo renderInfo)
    {
        LineSegment ascentLine = renderInfo.GetAscentLine();
        LineSegment descentLine = renderInfo.GetDescentLine();
        float[] yCoords = new float[]{
            ascentLine.GetStartPoint()[Vector.I2],
            ascentLine.GetEndPoint()[Vector.I2],
            descentLine.GetStartPoint()[Vector.I2],
            descentLine.GetEndPoint()[Vector.I2]
        };
        Array.Sort(yCoords);
        addVerticalUseSection(yCoords[0], yCoords[3]);
    }

    void addVerticalUseSection(float from, float to)
    {
        if (to < from)
        {
            float temp = to;
            to = from;
            from = temp;
        }

        int i=0, j=0;
        for (; i<verticalFlips.Count; i++)
        {
            float flip = verticalFlips[i];
            if (flip < from)
                continue;

            for (j=i; j<verticalFlips.Count; j++)
            {
                flip = verticalFlips[j];
                if (flip < to)
                    continue;
                break;
            }
            break;
        }
        bool fromOutsideInterval = i%2==0;
        bool toOutsideInterval = j%2==0;

        while (j-- > i)
            verticalFlips.RemoveAt(j);
        if (toOutsideInterval)
            verticalFlips.Insert(i, to);
        if (fromOutsideInterval)
            verticalFlips.Insert(i, from);
    }

    public List<float> verticalFlips = new List<float>();
}


public class HorizontalTextExtractionStrategy : LocationTextExtractionStrategy
{
    public class HorizontalTextChunk : TextChunk
    {
        public HorizontalTextChunk(String stringValue, Vector startLocation, Vector endLocation, float charSpaceWidth, TextLineFinder textLineFinder)
            : base(stringValue, startLocation, endLocation, charSpaceWidth)
        {
            this.textLineFinder = textLineFinder;
        }

        override public int CompareTo(TextChunk rhs)
        {
            if (rhs is HorizontalTextChunk)
            {
                HorizontalTextChunk horRhs = (HorizontalTextChunk) rhs;
                int rslt = CompareInts(getLineNumber(), horRhs.getLineNumber());
                if (rslt != 0) return rslt;
                return CompareFloats(StartLocation[Vector.I1], rhs.StartLocation[Vector.I1]);
            }
            else
                return base.CompareTo(rhs);
        }

        public override bool SameLine(TextChunk a)
        {
            if (a is HorizontalTextChunk)
            {
                HorizontalTextChunk horAs = (HorizontalTextChunk) a;
                return getLineNumber() == horAs.getLineNumber();
            }
            else
                return base.SameLine(a);
        }

        public int getLineNumber()
        {
            Vector startLocation = StartLocation;
            float y = startLocation[Vector.I2];
            List<float> flips = textLineFinder.verticalFlips;
            if (flips == null || flips.Count == 0)
                return 0;
            if (y < flips[0])
                return flips.Count / 2 + 1;
            for (int i = 1; i < flips.Count; i+=2)
            {
                if (y < flips[i])
                {
                    return (1 + flips.Count - i) / 2;
                }
            }
            return 0;
        }

        private static int CompareInts(int int1, int int2){
            return int1 == int2 ? 0 : int1 < int2 ? -1 : 1;
        }

        private static int CompareFloats(float float1, float float2)
        {
            return float1 == float2 ? 0 : float1 < float2 ? -1 : 1;
        }

        TextLineFinder textLineFinder;
    }

    public override void RenderText(TextRenderInfo renderInfo)
    {
        textLineFinder.RenderText(renderInfo);

        LineSegment segment = renderInfo.GetBaseline();
        if (renderInfo.GetRise() != 0){ // remove the rise from the baseline - we do this because the text from a super/subscript render operations should probably be considered as part of the baseline of the text the super/sub is relative to 
            Matrix riseOffsetTransform = new Matrix(0, -renderInfo.GetRise());
            segment = segment.TransformBy(riseOffsetTransform);
        }
        TextChunk location = new HorizontalTextChunk(renderInfo.GetText(), segment.GetStartPoint(), segment.GetEndPoint(), renderInfo.GetSingleSpaceWidth(), textLineFinder);
        getLocationalResult().Add(location);        
    }

    public HorizontalTextExtractionStrategy()
    {
        locationalResultField = typeof(LocationTextExtractionStrategy).GetField("locationalResult", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
        textLineFinder = new TextLineFinder();
    }

    List<TextChunk> getLocationalResult()
    {
        return (List<TextChunk>) locationalResultField.GetValue(this);
    }

    System.Reflection.FieldInfo locationalResultField;
    TextLineFinder textLineFinder;
}


    string extract(PdfReader reader, int pageNo)
    {
        return PdfTextExtractor.GetTextFromPage(reader, pageNo, new HorizontalTextExtractionStrategy());
    }

: LocationTextExtractionStrategy

iText 5.5.9-SNAPSHOT Commits 53526e4854fcb80c86cbc2e113f7a07401dc9a67 ( " LocationTextExtractionStrategy..." ) 1ab350beae148be2a4bef5e663b3d67a004ff9f8 ( " TextChunkLocation a Comparable < > class..." ), LocationTextExtractionStrategy , , .

, HorizontalTextExtractionStrategy. iText :

public class HorizontalTextExtractionStrategy2 extends LocationTextExtractionStrategy
{
    public static class HorizontalTextChunkLocationStrategy implements TextChunkLocationStrategy
    {
        public HorizontalTextChunkLocationStrategy(TextLineFinder textLineFinder)
        {
            this.textLineFinder = textLineFinder;
        }

        @Override
        public TextChunkLocation createLocation(TextRenderInfo renderInfo, LineSegment baseline)
        {
            return new HorizontalTextChunkLocation(baseline.getStartPoint(), baseline.getEndPoint(), renderInfo.getSingleSpaceWidth());
        }

        final TextLineFinder textLineFinder;

        public class HorizontalTextChunkLocation implements TextChunkLocation
        {
            /** the starting location of the chunk */
            private final Vector startLocation;
            /** the ending location of the chunk */
            private final Vector endLocation;
            /** unit vector in the orientation of the chunk */
            private final Vector orientationVector;
            /** the orientation as a scalar for quick sorting */
            private final int orientationMagnitude;
            /** 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 */
            private final int distPerpendicular;
            /** distance of the start of the chunk parallel to the orientation unit vector (i.e. the X position in an unrotated coordinate system) */
            private final float distParallelStart;
            /** distance of the end of the chunk parallel to the orientation unit vector (i.e. the X position in an unrotated coordinate system) */
            private final float distParallelEnd;
            /** the width of a single space character in the font of the chunk */
            private final float charSpaceWidth;

            public HorizontalTextChunkLocation(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);

                // see http://mathworld.wolfram.com/Point-LineDistance2-Dimensional.html
                // the two vectors we are crossing are in the same plane, so the result will be purely
                // in the z-axis (out of plane) direction, so we just take the I3 component of the result
                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 int orientationMagnitude()   {   return orientationMagnitude;    }
            public int distPerpendicular()      {   return distPerpendicular;       }
            public float distParallelStart()    {   return distParallelStart;       }
            public float distParallelEnd()      {   return distParallelEnd;         }
            public Vector getStartLocation()    {   return startLocation;           }
            public Vector getEndLocation()      {   return endLocation;             }
            public float getCharSpaceWidth()    {   return charSpaceWidth;          }

            /**
             * @param as the location to compare to
             * @return true is this location is on the the same line as the other
             */
            public boolean sameLine(TextChunkLocation as)
            {
                if (as instanceof HorizontalTextChunkLocation)
                {
                    HorizontalTextChunkLocation horAs = (HorizontalTextChunkLocation) as;
                    return getLineNumber() == horAs.getLineNumber();
                }
                else
                    return orientationMagnitude() == as.orientationMagnitude() && distPerpendicular() == as.distPerpendicular();
            }

            /**
             * Computes the distance between the end of 'other' and the beginning of this chunk
             * in the direction of this chunk orientation vector.  Note that it a bad idea
             * to call this for chunks that aren't on the same line and orientation, but we don't
             * explicitly check for that condition for performance reasons.
             * @param other
             * @return the number of spaces between the end of 'other' and the beginning of this chunk
             */
            public float distanceFromEndOf(TextChunkLocation other)
            {
                float distance = distParallelStart() - other.distParallelEnd();
                return distance;
            }

            public boolean isAtWordBoundary(TextChunkLocation previous)
            {
                /**
                 * Here we handle a very specific case which in PDF may look like:
                 * -.232 Tc [( P)-226.2(r)-231.8(e)-230.8(f)-238(a)-238.9(c)-228.9(e)]TJ
                 * The font charSpace width is 0.232 and it compensated with charSpacing of 0.232.
                 * And a resultant TextChunk.charSpaceWidth comes to TextChunk constructor as 0.
                 * In this case every chunk is considered as a word boundary and space is added.
                 * We should consider charSpaceWidth equal (or close) to zero as a no-space.
                 */
                if (getCharSpaceWidth() < 0.1f)
                    return false;

                float dist = distanceFromEndOf(previous);

                return dist < -getCharSpaceWidth() || dist > getCharSpaceWidth()/2.0f;
            }

            public int getLineNumber()
            {
                Vector startLocation = getStartLocation();
                float y = startLocation.get(Vector.I2);
                List<Float> flips = textLineFinder.verticalFlips;
                if (flips == null || flips.isEmpty())
                    return 0;
                if (y < flips.get(0))
                    return flips.size() / 2 + 1;
                for (int i = 1; i < flips.size(); i+=2)
                {
                    if (y < flips.get(i))
                    {
                        return (1 + flips.size() - i) / 2;
                    }
                }
                return 0;
            }

            @Override
            public int compareTo(TextChunkLocation rhs)
            {
                if (rhs instanceof HorizontalTextChunkLocation)
                {
                    HorizontalTextChunkLocation horRhs = (HorizontalTextChunkLocation) rhs;
                    int rslt = Integer.compare(getLineNumber(), horRhs.getLineNumber());
                    if (rslt != 0) return rslt;
                    return Float.compare(getStartLocation().get(Vector.I1), rhs.getStartLocation().get(Vector.I1));
                }
                else
                {
                    int rslt;
                    rslt = Integer.compare(orientationMagnitude(), rhs.orientationMagnitude());
                    if (rslt != 0) return rslt;

                    rslt = Integer.compare(distPerpendicular(), rhs.distPerpendicular());
                    if (rslt != 0) return rslt;

                    return Float.compare(distParallelStart(), rhs.distParallelStart());
                }
            }
        }
    }

    @Override
    public void renderText(TextRenderInfo renderInfo)
    {
        textLineFinder.renderText(renderInfo);
        super.renderText(renderInfo);
    }

    public HorizontalTextExtractionStrategy2() throws NoSuchFieldException, SecurityException
    {
        this(new TextLineFinder());
    }

    public HorizontalTextExtractionStrategy2(TextLineFinder textLineFinder) throws NoSuchFieldException, SecurityException
    {
        super(new HorizontalTextChunkLocationStrategy(textLineFinder));

        this.textLineFinder = textLineFinder;
    }

    final TextLineFinder textLineFinder;
}

(HorizontalTextExtractionStrategy2.java)

+4

, . . , . :

        Vector thisFacade = this.ascentLine.GetStartPoint().Subtract(this.descentLine.GetStartPoint());
        Vector infoFacade = renderInfo.GetAscentLine().GetStartPoint().Subtract(renderInfo.GetDescentLine().GetStartPoint());
        if (baseVector.Cross(ascent2base).Dot(baseVector.Cross(descent2base)) < 0
            && infoFacade.LengthSquared < thisFacade.LengthSquared - sameHeightThreshols)

Chistmass.

0

Source: https://habr.com/ru/post/1614225/

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