Getting Coordinates of string using ITextExtractionStrategy and LocationTextExtractionStrategy in Itextsharp

Question

I have a PDF file that i am reading into string using ITextExtractionStrategy.Now from the string i am taking a substring like My name is XYZ and need to get the rectangular coordinates of substring from the PDF file but not able to do it.On googling i got to know that LocationTextExtractionStrategy but not getting how to use this to get the coordinates.

Here is the code..

ITextExtractionStrategy strategy = new SimpleTextExtractionStrategy();
string currentText = PdfTextExtractor.GetTextFromPage(pdfReader, page, strategy);
currentText = Encoding.UTF8.GetString(ASCIIEncoding.Convert(Encoding.Default, Encoding.UTF8, Encoding.Default.GetBytes(currentText)));
text.Append(currentText);

string getcoordinate="My name is XYZ";

How can i get the rectangular coordinate of this substring using ITEXTSHARP..

Please help.

Answer 1

Here is a very, very simple version of an implementation.

Before implementing it is very important to know that PDFs have zero concept of "words", "paragraphs", "sentences", etc. Also, text within a PDF is not necessarily laid out left to right and top to bottom and this has nothing to do with non-LTR languages. The phrase "Hello World" could be written into the PDF as:

Draw H at (10, 10)
Draw ell at (20, 10)
Draw rld at (90, 10)
Draw o Wo at (50, 20)

It could also be written as

Draw Hello World at (10,10)

The ITextExtractionStrategy interface that you need to implement has a method called RenderText that gets called once for every chunk of text within a PDF. Notice I said "chunk" and not "word". In the first example above the method would be called four times for those two words. In the second example it would be called once for those two words. This is the very important part to understand. PDFs don't have words and because of this, iTextSharp doesn't have words either. The "word" part is 100% up to you to solve.

Also along these lines, as I said above, PDFs don't have paragraphs. The reason to be aware of this is because PDFs cannot wrap text to a new line. Any time that you see something that looks like a paragraph return you are actually seeing a brand new text drawing command that has a different y coordinate as the previous line. See this for further discussion.

The code below is a very simple implementation. For it I'm subclassing LocationTextExtractionStrategy which already implements ITextExtractionStrategy. On each call to RenderText() I find the rectangle of the current chunk (using Mark's code here) and storing it for later. I'm using this simple helper class for storing these chunks and rectangles:

//Helper class that stores our rectangle and text
public class RectAndText {
    public iTextSharp.text.Rectangle Rect;
    public String Text;
    public RectAndText(iTextSharp.text.Rectangle rect, String text) {
        this.Rect = rect;
        this.Text = text;
    }
}

And here's the subclass:

public class MyLocationTextExtractionStrategy : LocationTextExtractionStrategy {
    //Hold each coordinate
    public List<RectAndText> myPoints = new List<RectAndText>();

    //Automatically called for each chunk of text in the PDF
    public override void RenderText(TextRenderInfo renderInfo) {
        base.RenderText(renderInfo);

        //Get the bounding box for the chunk of text
        var bottomLeft = renderInfo.GetDescentLine().GetStartPoint();
        var topRight = renderInfo.GetAscentLine().GetEndPoint();

        //Create a rectangle from it
        var rect = new iTextSharp.text.Rectangle(
                                                bottomLeft[Vector.I1],
                                                bottomLeft[Vector.I2],
                                                topRight[Vector.I1],
                                                topRight[Vector.I2]
                                                );

        //Add this to our main collection
        this.myPoints.Add(new RectAndText(rect, renderInfo.GetText()));
    }
}

And finally an implementation of the above:

//Our test file
var testFile = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.Desktop), "test.pdf");

//Create our test file, nothing special
using (var fs = new FileStream(testFile, FileMode.Create, FileAccess.Write, FileShare.None)) {
    using (var doc = new Document()) {
        using (var writer = PdfWriter.GetInstance(doc, fs)) {
            doc.Open();

            doc.Add(new Paragraph("This is my sample file"));

            doc.Close();
        }
    }
}

//Create an instance of our strategy
var t = new MyLocationTextExtractionStrategy();

//Parse page 1 of the document above
using (var r = new PdfReader(testFile)) {
    var ex = PdfTextExtractor.GetTextFromPage(r, 1, t);
}

//Loop through each chunk found
foreach (var p in t.myPoints) {
    Console.WriteLine(string.Format("Found text {0} at {1}x{2}", p.Text, p.Rect.Left, p.Rect.Bottom));
}

I can't stress enough that the above does not take "words" into account, that'll be up to you. The TextRenderInfo object that gets passed into RenderText has a method called GetCharacterRenderInfos() that you might be able to use to get more information. You might also want to use GetBaseline() instead ofGetDescentLine()` if you don't care about descenders in the font.

EDIT

(I had a great lunch so I'm feeling a little more helpful.)

Here's an updated version of MyLocationTextExtractionStrategy that does what my comments below say, namely it takes a string to search for and searches each chunk for that string. For all the reasons listed this will not work in some/many/most/all cases. If the substring exists multiple times in a single chunk it will also only return the first instance. Ligatures and diacritics could also mess with this.

public class MyLocationTextExtractionStrategy : LocationTextExtractionStrategy {
    //Hold each coordinate
    public List<RectAndText> myPoints = new List<RectAndText>();

    //The string that we're searching for
    public String TextToSearchFor { get; set; }

    //How to compare strings
    public System.Globalization.CompareOptions CompareOptions { get; set; }

    public MyLocationTextExtractionStrategy(String textToSearchFor, System.Globalization.CompareOptions compareOptions = System.Globalization.CompareOptions.None) {
        this.TextToSearchFor = textToSearchFor;
        this.CompareOptions = compareOptions;
    }

    //Automatically called for each chunk of text in the PDF
    public override void RenderText(TextRenderInfo renderInfo) {
        base.RenderText(renderInfo);

        //See if the current chunk contains the text
        var startPosition = System.Globalization.CultureInfo.CurrentCulture.CompareInfo.IndexOf(renderInfo.GetText(), this.TextToSearchFor, this.CompareOptions);

        //If not found bail
        if (startPosition < 0) {
            return;
        }

        //Grab the individual characters
        var chars = renderInfo.GetCharacterRenderInfos().Skip(startPosition).Take(this.TextToSearchFor.Length).ToList();

        //Grab the first and last character
        var firstChar = chars.First();
        var lastChar = chars.Last();


        //Get the bounding box for the chunk of text
        var bottomLeft = firstChar.GetDescentLine().GetStartPoint();
        var topRight = lastChar.GetAscentLine().GetEndPoint();

        //Create a rectangle from it
        var rect = new iTextSharp.text.Rectangle(
                                                bottomLeft[Vector.I1],
                                                bottomLeft[Vector.I2],
                                                topRight[Vector.I1],
                                                topRight[Vector.I2]
                                                );

        //Add this to our main collection
        this.myPoints.Add(new RectAndText(rect, this.TextToSearchFor));
    }

You would use this the same as before but now the constructor has a single required parameter:

var t = new MyLocationTextExtractionStrategy("sample");