what the standard pdf scale(Millimeters,centimeters,inches)?

Question

i'm looking for write a special API to generate PDF, so... i'm using the text atributes/commands to build a pdf document through a simple text file.

I've already downloaded the pdf references manual, but i didn't found what i looking for.

What the standard pdf scale?

I need know the standard pdf scale to measure my line lenght, and change my width of "MediaBox".

Answer 1

The MediaBox, CropBox, BleedBox, TrimBox, and ArtBox are rectangles expressed in default user space units, cf. Table 30 – Entries in a page object in ISO 32000-1.

The size of this unit is defined by another Page dictionary entry (cf. the same table):

UserUnit number (Optional; PDF 1.6) A positive number that shall give the size of default user space units, in multiples of 1 ⁄ 72 inch. The range of supported values shall be implementation-dependent. Default value: 1.0 (user space unit is 1 ⁄ 72 inch).

The UserUnit is only used very rarely. Thus, most of the time the unit you are after is 1/72th inch.

BTW, it is called default user space unit because in a content stream you can constantly change the size of a unit in user space by using appropriate changes of the transformation and/or text matrices; thus, in the context of content streams this 1/72th inch is merely a starting value.