X and Y units about pdf-lib HOT 2 CLOSED

Hello @ithillel-aminev. The default unit is 1⁄72 inch.

This isn't currently mentioned anywhere in the docs. I'd definitely like to improve the docs and add more details and examples when I have the time. I've copied the relevant section(s) from the PDF specification below, in case you're interested. (Note that I certainly don't expect users of pdf-lib to consult this document when they have questions, it's just sometimes interesting to read things directly from the source.)

8.3.2.2 Device Space

The contents of a page ultimately appear on a raster output device such as a display or a printer. Such devices vary greatly in the built-in coordinate systems they use to address pixels within their imageable areas. A particular device’s coordinate system is called its device space. The origin of the device space on different devices can fall in different places on the output page; on displays, the origin can vary depending on the window system. Because the paper or other output medium moves through different printers and imagesetters in different directions, the axes of their device spaces may be oriented differently. For instance, vertical (y) coordinates may increase from the top of the page to the bottom on some devices and from bottom to top on others. Finally, different devices have different resolutions; some even have resolutions that differ in the horizontal and vertical directions.

8.3.2.3 User Space

To avoid the device-dependent effects of specifying objects in device space, PDF defines a device-independent coordinate system that always bears the same relationship to the current page, regardless of the output device on which printing or displaying occurs. This device-independent coordinate system is called user space.

The user space coordinate system shall be initialized to a default state for each page of a document. The CropBox entry in the page dictionary shall specify the rectangle of user space corresponding to the visible area of the intended output medium (display window or printed page). The positive x axis extends horizontally to the right and the positive y axis vertically upward, as in standard mathematical practice (subject to alteration by the Rotate entry in the page dictionary). The length of a unit along both the x and y axes is set by the UserUnit entry (PDF 1.6) in the page dictionary (see Table 30). If that entry is not present or supported, the default value of 1⁄72 inch is used. This coordinate system is called default user space.

NOTE: The default for the size of the unit in default user space (1⁄72 inch) is approximately the same as a point, a unit widely used in the printing industry. It is not exactly the same, however; there is no universal definition of a point.

from pdf-lib.

I'm going to close this now. Feel free to reopen it if you have additional questions 👍

from pdf-lib.