Group text lines if they are centered (#382)

[jstockwin]

Description

Add a check when checking if lines should be merged to see if they are centered above each other.

Fixes #382

Note: it might also be worth having a read of #383, as there is perhaps a discussion there about how to deal with these checks for a negative line margin...

How Has This Been Tested?

Example PDF

Here is my test code (which simply loads the pdfs and prints the elements):

from pdfminer import converter, pdfdocument, pdfinterp, pdfpage, pdfparser
from pdfminer.layout import LTTextContainer, LAParams
path_to_file = "centered_text_example.pdf"

with open(path_to_file, "rb") as pdf_file:
    parser = pdfparser.PDFParser(pdf_file)
    document = pdfdocument.PDFDocument(parser)
    resource_manager = pdfinterp.PDFResourceManager()
    device = converter.PDFPageAggregator(resource_manager, laparams=LAParams())
    interpreter = pdfinterp.PDFPageInterpreter(resource_manager, device)
    for page in pdfpage.PDFPage.create_pages(document):
        interpreter.process_page(page)
        results = device.get_result()
        elements = [
            element for element in results if isinstance(element, LTTextContainer)
        ]
device.close()

print(elements)

Before this change, you get:

[
    <LTTextBoxHorizontal(0) 123.800,344.802,216.392,367.878 'Long Text 1\n'>, 
    <LTTextBoxHorizontal(1) 146.100,366.002,194.070,411.778 'Text 1\nText 2\n'>, 
    <LTTextBoxHorizontal(2) 146.100,302.502,194.070,348.278 'Text 3\nText 4\n'>, 
    <LTTextBoxHorizontal(3) 39.700,24.176,43.200,42.152 ' \n'>, 
    <LTTextBoxHorizontal(4) 395.500,24.176,399.000,42.152 ' \n'>
]

After this change you get:

[
    <LTTextBoxHorizontal(0) 123.800,302.502,216.392,411.778 'Text 1\nText 2\nLong Text 1\nText 3\nText 4\n'>,
    <LTTextBoxHorizontal(1) 39.700,24.176,43.200,42.152 ' \n'>
    <LTTextBoxHorizontal(2) 395.500,24.176,399.000,42.152 ' \n'>
]

(The last two elements in each are just artefacts in the example pdf, ignore them).

Checklist

I will do these things once I get a bit of guidance on whether this is an acceptable change. I'll also need a pointer on how to add a relevant test.

• I have added tests that prove my fix is effective or that my feature works
• I have updated the README.md and other documentation, or I am sure that this is not necessary
• I have added a consice human-readable description of the change to CHANGELOG.md
• I have added docstrings to newly created methods and classes
• I have optimized the code at least one time after creating the initial version

[pietermarsman]

I will do these things once I get a bit of guidance on whether this is an acceptable change.

It is

I'll also need a pointer on how to add a relevant test.

Look at tests/test_layout.py for inspiration.

[pietermarsman]

Looks good!

[jstockwin]

@pietermarsman I've added 4 new commits, addressing your comments and then adding tests.

I couldn't find any tests for the function I've changed, but think what I added tests it fairly well (even if it takes a while of figuring out bounding boxes to work out what it's doing....).

Before my change, this test would fail because the centrally_aligned_overlapping text boxes would not be included.

Please could you take a look?

[pietermarsman]

I love the new *_aligned_with methods. They make find_neighbours() so much easier to read. Also the tests are really good :)

I've left 3 small cosmetic suggestions.

[jstockwin]

@pietermarsman PR updated with your comments

[pietermarsman]

Looks good!