Is there any PDF command, that scales rectangle coordinates? - pdf

Question

I have an application, that extracts text and rectangles from pdf files for further analysis. I use ItextSharp for extraction, and everything worked smoothly, until I stumbled upon a document, which has some strange table cell rectangles. The values in the drawing commands, that I retrieve, seem 10 times larger, than actual dimensions of the latter rectangles.
Just an example :
2577 831.676 385.996 3.99609 re
At the same time, when viewing the document all rectangles seem to correctly fit in the bounds of document pages. My guess is that there should be some scaling command, telling, that these values should be scaled down. Is the assumption right, or how is it possible, that such large rectangles are rendered so, that they stay inside the bounds of a page ?
The pdf document is behind this link : https://www.dropbox.com/s/gyvon0dwk6a9cj0/prEVS_ISO_11620_KOM_et.pdf?dl=0
The code, that handles extraction of dimensions from PRStream is as follows :
private static List<PdfRect> GetRectsAndLinesFromStream(PRStream stream)
{
var streamBytes = PdfReader.GetStreamBytes(stream);
var tokenizer = new PRTokeniser(new RandomAccessFileOrArray(streamBytes));
List<string> newBuf = new List<string>();
List<PdfRect> rects = new List<PdfRect>();
List<string> allTokens = new List<string>();
float[,] ctm = null;
List<float[,]> ctms = new List<float[,]>();
//if current ctm has not yet been added to list
bool pendingCtm = false;
//format definition for string-> float conversion
var format = new System.Globalization.NumberFormatInfo();
format.NegativeSign = "-";
while (tokenizer.NextToken())
{
//Add them to our master buffer
newBuf.Add(tokenizer.StringValue);
if (
tokenizer.TokenType == PRTokeniser.TokType.OTHER && newBuf[newBuf.Count - 1] == "re"
)
{
float startPointX = (float)double.Parse(newBuf[newBuf.Count - 5], format);
float startPointY = (float)double.Parse(newBuf[newBuf.Count - 4], format);
float width = (float)double.Parse(newBuf[newBuf.Count - 3], format);
float height = (float)double.Parse(newBuf[newBuf.Count - 2], format);
float endPointX = startPointX + width;
float endPointY = startPointY + height;
//if transformation is defined, correct coordinates
if (ctm!=null)
{
//extract parameters
float a = ctm[0, 0];
float b = ctm[0, 1];
float c = ctm[1, 0];
float d = ctm[1, 1];
float e = ctm[2, 0];
float f = ctm[2, 1];
//reverse transformation to get x and y from x' and y'
startPointX = (startPointX - startPointY * c - e) / a;
startPointY = (startPointY - startPointX * b - f) / d;
endPointX = (endPointX - endPointY * c - e) / a;
endPointY = (endPointY - endPointX * b - f) / d;
}
rects.Add(new PdfRect(startPointX, startPointY , endPointX , endPointY ));
}
//store current ctm
else if (tokenizer.TokenType == PRTokeniser.TokType.OTHER && newBuf[newBuf.Count - 1] == "q")
{
if (ctm != null)
{
ctms.Add(ctm);
pendingCtm = false;
}
}
//fetch last ctm and remove it from list
else if (tokenizer.TokenType == PRTokeniser.TokType.OTHER && newBuf[newBuf.Count - 1] == "Q")
{
if (ctms.Count > 0)
{
ctm = ctms[ctms.Count - 1];
ctms.RemoveAt(ctms.Count -1 );
}
}
else if (tokenizer.TokenType == PRTokeniser.TokType.OTHER && newBuf[newBuf.Count - 1] == "cm")
{
// x' = x*a + y*c + e ; y' = x*b + y*d + f
float a = (float)double.Parse(newBuf[newBuf.Count - 7], format);
float b = (float)double.Parse(newBuf[newBuf.Count - 6], format);
float c = (float)double.Parse(newBuf[newBuf.Count - 5], format);
float d = (float)double.Parse(newBuf[newBuf.Count - 4], format);
float e = (float)double.Parse(newBuf[newBuf.Count - 3], format);
float f = (float)double.Parse(newBuf[newBuf.Count - 2], format);
float[,] tempCtm = ctm;
ctm = new float[3, 3] {
{a,b,0},
{c,d,0},
{e,f,1}
};
//multiply matrices to form 1 transformation matrix
if (pendingCtm && tempCtm != null)
{
float[,] resultantCtm;
if (!TryMultiplyMatrix(tempCtm, ctm, out resultantCtm))
{
throw new InvalidOperationException("Invalid transform matrix");
}
ctm = resultantCtm;
}
//current CTM has not yet been saved to stack
pendingCtm = true;
}
return rects;
}

Answer 1

The command you are looking for is cm. Did you read The ABC of PDF with iText? The book isn't finished yet, but you can already download the first five chapters.
This is a screen shot of the table that shows the cm operator:
This is an example of 5 shapes that are created in the exact same way, using identical syntax:
They are added at different positions, even in a different size and shape, because of the change in the graphics state: the coordinate system was changed, and the shapes are rendered in that altered coordinate system.