How is 'upright' property defined?

[JankowskiKamil]

Hello,

I use this amazing library and sometimes have a problem with vertical / not upright chars. Is there any chance to get chars rotation value? I suspect that in cases where upright property is miscalculated, the rotation is equal to 89.99999... not 90.

I try to find the problem and wonder if this value is based on: upright = True if rotation == 90 else False, but I can't find the line of code responsible for this.

Unfortunately, I can't send a PDF file

[jsvine]

Hi @JankowskiKamil, and great question. The upright property comes directly from pdfminer.six, the dependency we use to get char/rect/etc.-level information. Specifically, it is computed here: https://github.com/pdfminer/pdfminer.six/blob/43c8fc8557528463c99598049b7005ae96ab8084/pdfminer/layout.py#L379

As you'll see from that part of the code, upright is computed from object's self.matrix property and a local variable scaling:

        (a, b, c, d, e, f) = self.matrix
        self.upright = 0 < a * d * scaling and b * c <= 0

The self.matrix property is more straightforward, since pdfminer.six exposes it and pdfplumber could extract it. In fact, PR #100 proposed this a while ago, and I mentioned adding this as a possibility in #368 (comment). Due to time constraints, I haven't yet done this. But your question reminds me that it would be a useful thing, and I'll see if I can do something about it.

[jsvine]

Update: Just pushed an attempt at making the current transformation matrix (CTM) accessible for characters, and introduced a class (pdfplumber.ctm.CTM) for calculating its scale, skew, and translation: ae6f99e

It turns out that CTMs achieve rotation by combining scale and skew. In most standard cases, it seems, rotation will be equal to the x-axis skew. So, to calculate the rotation, you can run something like this:

from pdfplumber.ctm import CTM
my_char = pdf.pages[0].chars[3]
my_char_ctm = CTM(*my_char["matrix"])
my_char_rotation = my_char_ctm.skew_x

To test this out, you can install the unreleased code via pip install -e git+https://github.com/jsvine/pdfplumber.git@feature-ctm

If you get the chance, please let me know whether it suits your particular situation.

[JankowskiKamil]

oh sorry, I didn't see this answer and i forgot the code a long time ago, but I think the first one helped me a lot :D