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pdftract/notes/pdftract-2rkc1.md
jedarden fda17d4d77 feat(pdftract-2rkc1): implement column confirmation with >= 3 line threshold 
Implement confirm_columns function that partitions page into candidate
columns (regions between consecutive gaps + before-first + after-last),
counts unique lines whose first span's x0 falls within each candidate's
x-range, and promotes candidates with line_count >= 3 to confirmed columns.

Supporting code:
- ColumnGap struct with lo/hi bounds, width(), midpoint()
- detect_column_gaps function for zero-coverage region detection
- HasFirstSpan trait for first span bbox access
- CandidateColumn struct for tracking x_range and line_count

All 49 column tests pass, including all acceptance criteria.

Bead: pdftract-2rkc1

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-27 23:09:01 -04:00

2.7 KiB
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pdftract-2rkc1: Column confirmation verification

Work completed

The confirm_columns function has been implemented in /home/coding/pdftract/crates/pdftract-core/src/layout/columns.rs (lines 252-332).

Implementation details

The implementation follows the algorithm specified in the plan:

  1. No gaps case (lines 257-274): Entire page is one candidate column. Counts lines whose first span's x0 falls within page bounds. Returns single column if >= 3 lines.

  2. Candidate column construction (lines 276-308):

    • Before-first gap: (0, gap_0.lo)
    • Between consecutive gaps: (gap_i.hi + 1, gap_i+1.lo)
    • After-last gap: (gap_last.hi + 1, page_width)

  3. Line counting (lines 310-321): For each line, gets first span's bbox via HasFirstSpan trait, checks if x0 falls within candidate column range, counts unique lines.

  4. Column promotion (lines 324-329): Filters candidates with line_count >= 3 to confirmed columns, reassigns indices left-to-right.

Supporting code added

  • ColumnGap struct (lines 89-116): Represents a gap in the x0 histogram with lo/hi bounds, width(), and midpoint() methods.
  • detect_column_gaps function (lines 156-201): Finds zero-coverage regions >= 3% of page width.
  • HasFirstSpan trait (lines 334-343): Trait for accessing first span's bbox.
  • CandidateColumn struct (lines 203-213): Internal tracking of x_range and line_count.
  • Column struct (lines 372-396): Confirmed column with index and x_range.

Test results

All 49 column tests pass, including all acceptance criteria:

Acceptance criteria Test Result
2-column page with 30 lines each: both confirmed test_confirm_columns_two_column_both_confirmed PASS
2-column page with 30 lines + 2 lines: only 30-line column confirmed test_confirm_columns_two_column_one_confirmed PASS
Single column: 1 candidate -> confirmed test_confirm_columns_single_column_confirmed PASS
Empty page: 0 confirmed test_confirm_columns_empty_page PASS

Additional edge cases tested:

  • Exactly 3 lines (boundary case): PASS
  • Leading/trailing gaps: PASS
  • Lines in gap unassigned: PASS
  • Lines with no spans: PASS
  • Three-column layouts: PASS

Invariants verified

  • INV: 3-line minimum: The filter condition c.line_count >= 3 is enforced at line 326.
  • Lines in gaps remain unassigned: Lines whose first span's x0 falls in a gap region are not counted for any candidate column.
  • "First span" = leftmost post-sort: The HasFirstSpan trait provides the first (leftmost) span's bbox; within-line sorting is assumed to be done before calling confirm_columns.

Command used

cargo nextest run -p pdftract-core 'columns::'

Result: 49 passed, 2382 skipped (0 failed)