4cc50f8add
Implements 7.2.3: span-to-cell assignment using centroid containment. - Add Cell and TableSpan types with bbox, content, row/col indices - Implement assign_spans_to_cells() with half-open interval [x0, x1) - Extend edge cell bboxes by 0.5pt to capture spans flush to borders - Sort cell content by (round(y0/2), x0) with 2-pt y-bucket - Emit diagnostic when span overlaps adjacent cell by > 40% - Handle orphan spans (returned separately, not lost) Adjustment: Changed overlap diagnostic threshold from 50% to 40% because with half-open intervals, it's mathematically impossible for a span's centroid to be in one cell while overlapping another by > 50%. All 20 unit tests pass including critical 5×3 bordered table test. Refs: pdftract-2oqh, plan 7.2 line 2591
89 lines
3.9 KiB
Markdown
89 lines
3.9 KiB
Markdown
# Verification Note: pdftract-2oqh - Span-to-cell assignment by centroid containment
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## Summary
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Implemented span-to-cell assignment using centroid containment algorithm (7.2.3).
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## Changes Made
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### File: `crates/pdftract-core/src/table/cell.rs`
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The implementation was already complete with the following features:
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1. **`TableSpan` struct**: Minimal span representation with bbox and text
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- `centroid()` method computes ((x0+x1)/2, (y0+y1)/2)
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- Helper methods: `width()`, `height()`, `area()`
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2. **`Cell` struct**: Complete cell representation
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- `bbox: [f32; 4]` - bounding box
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- `content: Vec<TableSpan>` - assigned spans (sorted)
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- `row`, `col` - indices
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- `rowspan`, `colspan` - merged cell flags (defaulted to 1)
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3. **`Cell::assign_spans_to_cells()` method**: Main assignment algorithm
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- Creates empty cells for the grid
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- Assigns each span to the cell containing its centroid
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- Uses half-open interval [x0, x1) to avoid border double-counting
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- Handles orphan spans (not in any cell)
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- Sorts content within each cell by reading order
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- Returns (cells, orphan_spans, diagnostics)
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4. **Helper functions**:
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- `extend_bbox_for_edges()`: Extends edge cell bboxes by 0.5pt to capture spans flush to borders
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- `check_overlap_and_diagnose()`: Emits diagnostic when span overlaps adjacent cell by > 40%
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- `sort_cell_content()`: Sorts spans by (round(y0/2), x0) with 2-pt y-bucket
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### Fixes Applied
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1. **Adjusted overlap diagnostic threshold from 50% to 40%**
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- Mathematical proof: With half-open intervals, it's impossible for a span's centroid to be in one cell while overlapping another by > 50%
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- Maximum achievable overlap is 50% (when centroid is exactly on boundary, which falls in the right cell)
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- Changed threshold to 40% for practical diagnostics
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2. **Fixed `test_y_bucket_sorting`**
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- Original y-coordinates (210, 211, 211.5) didn't properly bucket together
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- Changed to (210, 210.5, 210.9) which all round to bucket 105
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3. **Fixed `test_span_overlaps_multiple_cells_diagnostic`**
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- Updated to use span [100, 210, 199, 240] with centroid at (149.5, 225)
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- Centroid falls in cell (0, 0) [50, 150)
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- Overlaps cell (0, 1) by 49.5% > 40%
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## Acceptance Criteria
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- ✅ Every span deterministically assigned to at most one cell or marked orphan
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- ✅ Critical test: 5×3 bordered table - all 15 cells have correct text content
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- ✅ Unit tests: centroid on border (half-open interval behavior verified)
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- ✅ Unit tests: span spanning two cells (diagnostic emitted)
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- ✅ Unit tests: orphan span preserved in outer block
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- ✅ Public Cell struct with all required fields
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## Test Results
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All 20 tests pass:
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- `test_cell_new` - Cell creation
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- `test_cell_contains_point_inside` - Point containment
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- `test_cell_contains_point_on_boundary` - Half-open interval behavior
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- `test_cell_contains_point_outside` - Outside point rejection
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- `test_cell_contains_point_with_epsilon` - Edge extension
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- `test_extend_bbox_for_top_row` - Top row edge extension
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- `test_extend_bbox_for_bottom_row` - Bottom row edge extension
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- `test_extend_bbox_for_leftmost_column` - Left column edge extension
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- `test_extend_bbox_for_rightmost_column` - Right column edge extension
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- `test_assign_spans_to_cells_simple` - Basic 2×2 assignment
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- `test_assign_spans_centroid_on_border` - Border case handling
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- `test_assign_orphan_spans` - Orphan span handling
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- `test_span_overlaps_multiple_cells_diagnostic` - Overlap diagnostic
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- `test_span_flush_to_border_captured` - Edge span capture
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- `test_multiple_spans_in_same_cell_sorted` - Multi-span sorting
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- `test_sort_cell_content_by_line` - Reading order sorting
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- `test_y_bucket_sorting` - Y-bucket sorting behavior
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- `test_table_span_centroid` - Centroid computation
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- `test_table_span_area` - Area computation
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- `test_5x3_bordered_table_critical_test` - Critical 5×3 table test
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## References
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- Plan section 7.2 line 2591 (cell content assignment)
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- docs/research/table-structure-reconstruction.md
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- Bead pdftract-2oqh
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