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How to set line length in centimeters and draw such a line (C# in WPF on Canvas)?

I do this, I programmatically get the dpi value (along the OX axis and along the OY axis is 144), I convert it to points (virt. pixels) per centimeter (equal to 56.69 points / cm),
from a given length in centimeters (for example, 10 cm) I turn into a length in points (equal to 566.93),
I draw this line on Canvas - as a result, the length of this line (in cm) is 30 percent (measured with a regular ruler) more than the originally specified length in cm. This does not suit!
The screen scale is set to 150%. Display resolution 1920*1080.
I define the dpi value (dots per inch) as follows
PresentationSource source = PresentationSource.FromVisual(this);
double dpiX = -1, dpiY = -1;
if (source != null)
{
dpiX = 96.0 * source.CompositionTarget.TransformToDevice.M11;
dpiY = 96.0 * source.CompositionTarget.TransformToDevice.M22;
}
Please, who faced it, prompt links, sources, the solution.

Text chunks getting positions as in html?

transform pdf points to pixels, worked correctly:
point-to-pixel = 1/72*300(DPI)
getting each text chunk positions (X,Y) in PDF the Y is calculated from
bottom-to-top, not as in standard html or java Script.
to get the Y value from top-to-down , cause not accurate Y position as in
html style , or win Form style.
how to get the correct Y top-to-down using any Page height, or rect mediaBox
or cropBox or rect textMarging finder ?
the code I used is your example of :
public class LocationTextExtractionStrategyClass : 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 = 0;// 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().ToList();//.Skip(startPosition).Take(this.TextToSearchFor.Length)
var charsText = renderInfo.GetText();
//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]
);
BaseColor curColor = new BaseColor(0f, 0f, 0f);
if (renderInfo.GetFillColor() != null)
curColor = renderInfo.GetFillColor();
//Add this to our main collection
myPoints.Add(new RectAndText(rect, charsText, curColor));//this.TextToSearchFor));
}
}//end-of-txtLocation-class//

You are asking many different questions in one post.
First let's start with the coordinate system in the PDF standard. Observe that I am talking about a standard, more specifically about ISO 32000. The coordinate system on a PDF page is explained in my answer to the Stack Overflow question How should I interpret the coordinates of a rectangle in PDF?
As you can see, a rectangle drawn in a PDF using a coordinate (llx, lly) for the lower-left corner and a coordinate (urx, ury) for the upper-right corner, assumes that the X-axis points to the right, and the Y-axis points upwards.
As for the width and the height of a page, that's explained in my answer to the Stack Overflow question How to Get PDF page width and Height?
For instance: you could have a /MediaBox that is defined as [0 0 595 842], and therefore measures 595 x 842 points (an A4 page), but that has a /CropBox that is defined as [5 5 590 837], which means that the visible area is only 585 x 832 points.
You also shouldn't assume that the lower-left corner of a page coincides with the (0, 0) coordinate. See Where is the Origin (x,y) of a PDF page?
When you create a document from scratch, a default margin of half an inch is used if you don't define a margin yourself. If you want to change the default, see Fit content on pdf size with iTextSharp?
Now for the height of a Chunk or, if you're using iText 7 (which you should, but —for some reason unknown to me— don't) the height of a Text object, this depends on the font size. The font size is an average size of the different glyphs in a font. If you look at the letter g, and you compare it with the letter h, you see that g takes more space under the baseline of the text than h, whereas h takes more space above the baseline than g.
If you want to calculate the exact space that is taken, read my answer to the question How to calculate the height of an element?
If the text snippet is used in the context of lines in a paragraph, you also have to take the leading into account: Changing text line spacing (Maybe that's not relevant in the context of your question, but it's good to know.)
If you have Chunk objects in iText 5, and you want to do specific things with these Chunks, you might benefit from using page events. See How to draw a line every 25 words?
If you want to add a colored background to a Chunk, it's even easier: How to set the paragraph of itext pdf file as rectangle with background color in Java
Update 1: All of the above may be irrelevant if you are looking to convert HTML to PDF. In that case, it's easy: use iText 7 + pdfHTML as described in Converting HTML to PDF using iText and all the Math is done by the pdfHTML add-on.
Update 2: There seems to be some confusion regarding the measurement units. The differences between user units, points and pixels is explained in the FAQ page How do the measurement systems in HTML relate to the measurement system in PDF?
Summarized:
1 in. = 25.4 mm = 72 user units by default (but it can be changed).
1 in. = 25.4 mm = 72 pt.
1 in. = 25.4 mm = 96 px.

How to Resize a Barcode?

I created a tool that generates PDF417 2D barcodes. The output png file is 290x78 pixels.
The reason behind this width and height is a formula used to create this symbol so that it is correctly read by bar code scanners.
My symbol is 13 columns and 39 rows.
This formula is:
Width = ((17 * # of columns) + 69) X + 2 (size of quiet zone)
Height = (# of rows) (row height) + 2 (size of quiet zone)
So:
17 * 13 + 69 = 290px
39 * 2 = 78px
My question is the software I use to create these bar codes allows you to save the file to this size but prints it at a different size.
These print parameters turn out to be as follow but I cannot figure out how to calculate them:
X Dimension (in) :0.0067
Y Dimension (in) :0.0133
Height x Width (in) :0.52 x 1.93
Height x Width (mm) :13.21 x 49.11
Rows x Columns : 39 x 13
Error Correction Level :5
Bytes Encoded :257
SLD Codeword :1
Data Codewords :157
Pad Codewords :285
MPDF Codewords :0
EC Codewords :64
Total Codewords :507
Here's a snapshot of the program I currently use:

This appears to be an issue of DPI and print size.
pixels/dpi=inches
or if you're going the other way
inches x dpi = pixels
You can set the DPI dropdown in your software to the necessary value.
See this calculator to play with the values: http://auctionrepair.com/pixels.html

Why is the barcode text value not printing beneath the barcode?

I am printing using the Windows Compact Framework to a Zebra belt printer using the OpenNetCF serial port class and CPCL. The printed label is pretty much as it should be, but the barcode value is not printing beneath the barcode as it should.
I create an ArrayList of commands to be sent the printer and then pass them one at a time to the serial port. If the controls that supply the values are empty, I use some dummy data, like so:
private void btnPrint_Click(object sender, System.EventArgs e)
{
string listPrice = txtList.Text;
if (listPrice.Trim() == string.Empty)
{
listPrice = "3.14";
}
string description = txtDesc.Text;
if (description.Trim() == string.Empty)
{
description = "The Life of Pi";
}
string barcode = txtUPC.Text;
if (barcode.Trim() == string.Empty)
{
barcode = "01701013992";
}
ArrayList arrList = new ArrayList();
arrList.Add("! 0 200 200 120 1\r\n"); // replace 120 with label height if different than 1.25"/120 pixels (at 96 pixels per inch)
arrList.Add("RIGHT\r\n");
arrList.Add(string.Format("TEXT 0 5 0 0 {0}\r\n", listPrice));
arrList.Add("LEFT\r\n");
arrList.Add(string.Format("TEXT 0 0 0 52 {0}\r\n", description));
arrList.Add("CENTER\r\n");
arrList.Add("BARCODE-TEXT 0 0 5\r\n");
arrList.Add(string.Format("BARCODE 128 1 1 50 0 77 {0}\r\n", barcode));
arrList.Add("FORM\r\n");
arrList.Add("PRINT\r\n");
PrintUtils pu = new PrintUtils();
pu.PrintLabel(arrList);
}
public void PrintLabel(ArrayList linesToSend)
{
using (SerialPort serialPort = new SerialPort())
{
serialPort.BaudRate = 19200;
serialPort.Handshake = Handshake.XOnXOff;
serialPort.DataBits = 8;
serialPort.Parity = Parity.None;
serialPort.StopBits = StopBits.One;
serialPort.PortName = "COM1:";
serialPort.Open();
Thread.Sleep(500); //this may not even be necessary and, if so, a different value may be better
foreach (string line in linesToSend)
{
serialPort.Write(line);
}
serialPort.Close();
}
}
...the problem is that the label (when I allow the dummy data to print) should be:
3.14
The Life of Pi
<barcode here>
01701013992
...and here's what is really printing:
3.14
The Life of Pi
<barcode here>
[blank]
So the problem is that the barcode as text ("01701013992") is not printing beneath the barcode.
Does anybody know why this is occurring even though I've got a BARCODE-TEXT command in there, and how to rectify it?
UPDATE
A key piece of info came my way, namely that the label height (in my case) should be 254, not 120 (for my 1.25" in height label, I was calculating based on 96 pixels == 1 inch, but in actuality this particular printer is 203 dpi, so 1.25 X == 254 (more precisely 253.75, but 254 is close enough).
So the code has changed to this:
// Command args (first line, prepended with a "!": horizontal (X) pos, resolution, resolution, label height, copies
// TEXT args are: fontNumber, fontSizeIdentifier, horizontal (X) pos, vertical (Y) pos
// BARCODE args are: barcodeType, unitWidthOfTheNarrowBar, ratioOfTheWideBarToTheNarrowBar, unitHeightOfTheBarCode,
// horizontal (X) pos, vertical (Y) pos, barcodeValue
// BARCODE-TEXT args are: fontNumber, fontSizeIdentifier, space between barcode and -text
// 1 inch = 203 dots (Zebra QL220 is a 203 dpi printer); font 4,3 == 90 pixels; font 2,0 == 12 pixels
arrList.Add("! 0 200 200 254 1\r\n"); // 203 dpi X 1.25 = 254
arrList.Add("RIGHT\r\n");
arrList.Add(string.Format("TEXT 4 3 0 0 {0}\r\n", listPrice));
arrList.Add("LEFT\r\n");
arrList.Add(string.Format("TEXT 2 0 0 100 {0}\r\n", description));
arrList.Add("BARCODE-TEXT 2 0 5\r\n");
arrList.Add("CENTER\r\n");
arrList.Add(string.Format("BARCODE 128 1 1 50 0 120 {0}\r\n", barcode));
arrList.Add("FORM\r\n");
arrList.Add("PRINT\r\n");
...but I'm STILL not seeing the description label - except for a lonely "P" below the "3" and the "." in the price.
Are my calculations wrong, or what?
Here's what I'm thinking I have:
Label is 254 dots/1.25" high.
First line starts at YPos 0 and prints "3.14" in a 90 pixel font, right-aligned. That prints fine.
Second line starts at YPos 100 (10 dots below the 90-dot first line), left-aligned. All I see is the aforementioned "P" in what seems to be the right size.
Third line is the barcode, at YPos (120), centered; prints fine
Fourth/final line is the barcode as text beneath the barcode proper, centered; prints fine.
NOTE: I can't put a bounty on this yet, but anybody who solves it I will award 100 points as soon as I'm able (in two days, I reckon).

It turns out that the problem was that I was using font # 2 in order to get a font size of 12 (it is the only font that provides that size). The problem with font # 2 is that it is "OCR-A" and as such only prints certain characters. In the string I was passing as a test ("The Life of Pi", to go along with the list price of 3.14), the only character it recognizes in that string is P. So that's why it's the only one I saw.
I had to increase my font size to the next available, namely 24, using font #5 (Manhattan) or 7 (Warwick).
"mk" from zebra provided me with this information ("The OCR font is a special font that doesn’t include all characters that you are trying to print.").
If you look at Appendix D in the CPCL programming manual, it does show font #2 as being "OCR-A," but it didn't dawn on me that that meant it's character set precluded most alpha characters. Even if that's obvious to some, it seems to me that should be emphasized in the manual: When printing text, don't use font #2!
Note: Font #6 (MICR) is also to be avoided for text.

Finding a percentage

Here's the problem. I have a picture that will have a different Height every time according to the picture that's loaded.
I'd like to scale that picture so it fits inside of the document which has 800 pixels height. So if the image has 2560px in height, I need to find out the PERCENTAGE needed to bring that pixel height down to 750 so it fits snuggly on the page.
I'm stuck trying to find the formula for this simple enough problem.
Here's my code:
iTextSharp.text.Image pic = iTextSharp.text.Image.GetInstance(
image, System.Drawing.Imaging.ImageFormat.Jpeg);
if (pic.Height > pic.Width)
{
//Maximum height is 800 pixels.
pic.Height formula goes here....
}
else
{
//Maximum width is 600 pixels.
pic.Width formula goes here....
}

Some number p is such that p * 2560 = 750. Therefore, p = 750 / 2560 = 0.29296875.
Of course, make sure that you do floating-point division.

The rule of three will help you sort it out.

I don't know if I understand your problem exactly. Do you mean something like this?
percentage = (frameHeight / picHeight) * 100
Example:
(750 / 2560) * 100 = 29
That means: 2560 * 0.29 = 750

Here x is the maximum desired height, y is the actual image height and p is the percentage.
p = x / y;
x = p * y;
y = x / p;
Given any two you can find the other.