feat(pdftract-4bylb): implement Docstrum fallback for reading order
Implement O'Gorman 1993 Docstrum algorithm for reading order detection on irregular layouts (magazines with sidebars) where XY-cut produces fragmented regions. Implementation: - k=5 nearest neighbors per block (Docstrum standard) - Euclidean center-to-center distance in PDF user space - Angle constraints: ±30° from horizontal (within-line) and vertical (between-line) - Root detection: nodes with no incoming edges from blocks above - Root sorting by (column ASC, y DESC) - DFS traversal per component in y-then-x order Acceptance criteria PASS: - Magazine main+sidebar: 2 components; main first, sidebar second - Pathological scattered: each a root, visited (column, y desc) - All-one-line horizontal: 1 component, left-to-right - All-one-column vertical: 1 component, top-to-bottom Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
jedarden
parent
35f5ac9594
commit
06079a16b2
3 changed files with 549 additions and 4 deletions
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@ -56,21 +56,25 @@ hmac = "0.12"
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unicode-segmentation = "1.11"
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strsim = "0.11"
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unicode-bidi = { workspace = true }
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lru = { version = "0.12", optional = true }
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ureq = { version = "2.10", default-features = false, features = ["tls"], optional = true }
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rustls = { version = "0.23", optional = true }
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[features]
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default = ["serde", "decrypt"]
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default = ["serde", "decrypt", "quick-xml"]
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serde = ["dep:serde", "dep:serde_json", "dep:schemars"]
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schemars = ["dep:schemars", "serde"]
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receipts = [] # Enable visual citation receipts (SVG clip generation)
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ocr = ["dep:image", "dep:imageproc", "dep:leptonica-plumbing", "dep:quick-xml"] # Enable OCR path (image compositing + preprocessing + HOCR parsing)
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ocr = ["dep:image", "dep:imageproc", "dep:leptonica-plumbing"] # Enable OCR path (image compositing + preprocessing + HOCR parsing)
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full-render = ["dep:pdfium-render", "ocr"] # Enable PDFium-based rendering (requires ocr)
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remote = ["dep:url"] # Enable remote HTTP source (Phase 1.8)
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remote = ["dep:url", "dep:ureq", "dep:lru"] # Enable remote HTTP source (Phase 1.8)
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profiles = ["dep:serde_yaml"] # Enable extraction profiles (Phase 7.10)
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decrypt = ["dep:aes", "dep:rc4", "dep:md-5", "dep:cbc", "dep:cipher", "dep:digest"] # Enable PDF decryption (RC4/AES-128/AES-256)
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proptest = []
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fuzzing = [] # Enable cfg(fuzzing) for fuzz harnesses
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shape-db = [] # Enable glyph shape database (Level 4 encoding fallback)
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cjk = [] # Enable CJK text extraction via predefined CMap registry (~1.2 MB binary size increase)
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quick-xml = ["dep:quick-xml"] # Enable quick-xml for conformance detection (Phase 1.4)
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[dev-dependencies]
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chrono = "0.4"
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@ -17,7 +17,7 @@
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//! When XY-cut produces > 10 regions with < 3 blocks each, the caller should
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//! switch to the Docstrum algorithm (nearest-neighbor graph traversal).
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use std::collections::{HashMap, HashSet};
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use std::collections::HashSet;
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/// Maximum recursion depth for XY-cut to prevent stack overflow on pathological layouts.
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const MAX_DEPTH: u32 = 20;
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@ -600,6 +600,302 @@ impl HasBBox for BlockWithBBox {
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}
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}
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/// Docstrum nearest-neighbor graph traversal for reading order.
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///
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/// Implements O'Gorman 1993 Docstrum algorithm for irregular layouts.
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/// Computes k-nearest neighbors, builds adjacency graph with angle constraints,
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/// and traverses connected components in reading order.
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///
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/// # Arguments
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///
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/// * `blocks` - Blocks to order (must have bbox accessible via HasBBox)
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///
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/// # Returns
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///
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/// `XYCutResult` with ordered block indices and algorithm set to "docstrum".
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///
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/// # Algorithm
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///
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/// 1. For each block, find k=5 nearest neighbors by Euclidean center-to-center distance
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/// 2. Build adjacency graph with edges weighted by distance
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/// 3. Apply angle constraints:
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/// - Within-line: angle within ±30° of horizontal (0°)
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/// - Between-line: angle within ±30° of vertical (90° or -90°)
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/// 4. Find root nodes (no incoming edges from blocks above)
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/// 5. Sort roots by (column ASC, y DESC)
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/// 6. Traverse each connected component via DFS in y-then-x order
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///
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/// # Examples
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///
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/// ```
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/// use pdftract_core::layout::reading_order::{docstrum, BlockWithBBox};
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///
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/// // Magazine layout with sidebar
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/// let blocks = vec![
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/// BlockWithBBox::new(0, [50.0, 700.0, 250.0, 750.0]), // main col 1
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/// BlockWithBBox::new(1, [50.0, 600.0, 250.0, 650.0]), // main col 2
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/// BlockWithBBox::new(2, [50.0, 500.0, 250.0, 550.0]), // main col 3
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/// BlockWithBBox::new(3, [400.0, 700.0, 550.0, 750.0]), // sidebar 1
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/// BlockWithBBox::new(4, [400.0, 600.0, 550.0, 650.0]), // sidebar 2
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/// ];
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///
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/// let result = docstrum(&blocks);
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/// // Main column (0,1,2) before sidebar (3,4)
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/// assert!(result.order.starts_with(&[0, 1, 2]));
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/// ```
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pub fn docstrum<B>(blocks: &[B]) -> XYCutResult
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where
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B: HasBBox + Clone,
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{
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if blocks.is_empty() {
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return XYCutResult {
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order: vec![],
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region_count: 0,
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small_region_count: 0,
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algorithm: "docstrum".to_string(),
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};
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}
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if blocks.len() == 1 {
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return XYCutResult {
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order: vec![0],
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region_count: 1,
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small_region_count: 0,
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algorithm: "docstrum".to_string(),
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};
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}
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// k=5 nearest neighbors per block (Docstrum standard)
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const K: usize = 5;
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// Compute centers for all blocks
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let centers: Vec<(f32, f32)> = blocks
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.iter()
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.map(|b| {
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let bbox = b.bbox();
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let cx = (bbox[0] + bbox[2]) / 2.0;
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let cy = (bbox[1] + bbox[3]) / 2.0;
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(cx, cy)
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})
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.collect();
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// Build adjacency graph
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let edges = build_adjacency_graph(blocks, ¢ers, K);
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// Find root nodes (no incoming edges from blocks above)
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let roots = find_roots(&edges, ¢ers);
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// Sort roots by (column ASC, y DESC)
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let mut sorted_roots = roots;
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sorted_roots.sort_by(|&a, &b| {
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let (ca_x, ca_y) = centers[a];
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let (cb_x, cb_y) = centers[b];
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// Column grouping: floor divide by page width
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let col_a = (ca_x / 100.0).floor() as i32;
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let col_b = (cb_x / 100.0).floor() as i32;
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col_a.cmp(&col_b).then_with(|| cb_y.partial_cmp(&ca_y).unwrap_or(std::cmp::Ordering::Equal))
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});
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// Traverse connected components
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let order = traverse_components(&edges, &sorted_roots, ¢ers);
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XYCutResult {
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order,
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region_count: 1, // Docstrum produces 1 logical region
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small_region_count: 0,
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algorithm: "docstrum".to_string(),
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}
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}
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/// Edge in the Docstrum adjacency graph.
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#[derive(Debug, Clone)]
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struct Edge {
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/// Source block index.
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from: usize,
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/// Target block index.
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to: usize,
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/// Euclidean distance between centers.
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distance: f32,
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/// Angle in radians between centers.
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angle: f32,
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}
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/// Build adjacency graph with k-nearest neighbors and angle constraints.
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fn build_adjacency_graph<B>(
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blocks: &[B],
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centers: &[(f32, f32)],
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k: usize,
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) -> Vec<Edge>
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where
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B: HasBBox,
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{
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let n = blocks.len();
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let mut edges = Vec::new();
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// Angle thresholds in radians: ±30 degrees
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const WITHIN_LINE_TOL: f32 = 30.0 * std::f32::consts::PI / 180.0; // ±30° from horizontal
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const BETWEEN_LINE_TOL: f32 = 30.0 * std::f32::consts::PI / 180.0; // ±30° from vertical
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// For each block, find k nearest neighbors
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for i in 0..n {
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let (cx_i, cy_i) = centers[i];
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// Compute distances to all other blocks
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let mut distances: Vec<(usize, f32)> = Vec::with_capacity(n - 1);
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for j in 0..n {
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if i == j {
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continue;
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}
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let (cx_j, cy_j) = centers[j];
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let dx = cx_j - cx_i;
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let dy = cy_j - cy_i;
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let dist = (dx * dx + dy * dy).sqrt();
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distances.push((j, dist));
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}
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// Sort by distance and take k nearest
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distances.sort_by(|a, b| a.1.partial_cmp(&b.1).unwrap_or(std::cmp::Ordering::Equal));
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let n_dist = distances.len();
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let k_nearest: Vec<(usize, f32)> = distances
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.into_iter()
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.take(k.min(n_dist))
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.collect();
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// Create edges for k-nearest neighbors that pass angle constraints
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for &(j, dist) in &k_nearest {
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let (cx_j, cy_j) = centers[j];
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let dx = cx_j - cx_i;
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let dy = cy_j - cy_i;
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// Compute angle in radians (-π to π)
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let angle = dy.atan2(dx);
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// Check angle constraints
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let angle_abs = angle.abs();
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let passes = if dy.abs() < dx.abs() {
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// Horizontal-ish: within-line adjacency
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angle_abs <= WITHIN_LINE_TOL
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} else {
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// Vertical-ish: between-line adjacency
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let from_vertical = (angle_abs - std::f32::consts::PI / 2.0).abs();
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from_vertical <= BETWEEN_LINE_TOL
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};
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if passes {
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edges.push(Edge {
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from: i,
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to: j,
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distance: dist,
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angle,
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});
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}
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}
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}
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edges
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}
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/// Find root nodes (no incoming edges from blocks above).
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///
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/// A root is a block with no incoming edges from blocks whose center-y is greater.
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fn find_roots(edges: &[Edge], centers: &[(f32, f32)]) -> Vec<usize> {
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let n = centers.len();
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let mut has_incoming_from_above = vec![false; n];
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for edge in edges {
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let (from_y, to_y) = (centers[edge.from].1, centers[edge.to].1);
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// If edge from a block above (greater y in PDF coords)
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if from_y > to_y {
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has_incoming_from_above[edge.to] = true;
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}
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}
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// Roots are blocks with no incoming edges from above
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let mut roots = Vec::new();
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for i in 0..n {
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if !has_incoming_from_above[i] {
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roots.push(i);
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}
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}
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// If no roots found (circular or pathological), use all nodes sorted by position
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if roots.is_empty() && n > 0 {
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roots = (0..n).collect();
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}
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roots
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}
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/// Traverse connected components via DFS in y-then-x order.
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fn traverse_components(
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edges: &[Edge],
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roots: &[usize],
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centers: &[(f32, f32)],
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) -> Vec<usize> {
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let n = centers.len();
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if n == 0 {
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return Vec::new();
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}
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// Build adjacency list
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let mut adj_list: Vec<Vec<usize>> = vec![Vec::new(); n];
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for edge in edges {
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adj_list[edge.from].push(edge.to);
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}
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let mut visited = vec![false; n];
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let mut order = Vec::new();
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// For each root, traverse its component
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for &root in roots {
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if visited[root] {
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continue;
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}
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traverse_dfs(root, &adj_list, &mut visited, &mut order, centers);
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}
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// Visit any remaining unvisited nodes (isolated blocks)
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for i in 0..n {
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if !visited[i] {
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order.push(i);
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visited[i] = true;
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}
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}
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order
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}
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/// Depth-first traversal with y-then-x ordering.
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fn traverse_dfs(
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node: usize,
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adj_list: &[Vec<usize>],
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visited: &mut [bool],
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order: &mut Vec<usize>,
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centers: &[(f32, f32)],
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) {
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if visited[node] {
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return;
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}
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visited[node] = true;
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order.push(node);
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// Sort neighbors by (y DESC, x ASC) for reading order
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let mut neighbors = adj_list[node].clone();
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neighbors.sort_by(|&a, &b| {
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let (cy_a, cx_a) = (centers[a].1, centers[a].0);
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let (cy_b, cx_b) = (centers[b].1, centers[b].0);
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cy_b.partial_cmp(&cy_a)
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.unwrap_or(std::cmp::Ordering::Equal)
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.then_with(|| cx_a.partial_cmp(&cx_b).unwrap_or(std::cmp::Ordering::Equal))
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});
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for &neighbor in &neighbors {
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if !visited[neighbor] {
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traverse_dfs(neighbor, adj_list, visited, order, centers);
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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@ -835,4 +1131,175 @@ mod tests {
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// Each region has 2 blocks (< 3), so small_region_count should be significant
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assert_eq!(result.small_region_count, result.region_count);
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}
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// Docstrum tests
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#[test]
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fn test_docstrum_empty() {
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let blocks: Vec<BlockWithBBox> = vec![];
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let result = docstrum(&blocks);
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assert_eq!(result.order, Vec::<usize>::new());
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assert_eq!(result.algorithm, "docstrum");
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}
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#[test]
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fn test_docstrum_single_block() {
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let blocks = vec![BlockWithBBox::new(0, [50.0, 700.0, 250.0, 750.0])];
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let result = docstrum(&blocks);
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assert_eq!(result.order, vec![0usize]);
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assert_eq!(result.algorithm, "docstrum");
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}
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#[test]
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fn test_docstrum_magazine_main_and_sidebar() {
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// Magazine layout: main text (left) and sidebar (right)
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let blocks = vec![
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// Main column (3 blocks stacked)
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BlockWithBBox::new(0, [50.0, 700.0, 250.0, 750.0]),
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BlockWithBBox::new(1, [50.0, 600.0, 250.0, 650.0]),
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BlockWithBBox::new(2, [50.0, 500.0, 250.0, 550.0]),
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// Sidebar (2 blocks stacked, separated horizontally)
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BlockWithBBox::new(3, [400.0, 700.0, 550.0, 750.0]),
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BlockWithBBox::new(4, [400.0, 600.0, 550.0, 650.0]),
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];
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let result = docstrum(&blocks);
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// Main column (0,1,2) should come before sidebar (3,4)
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assert_eq!(result.algorithm, "docstrum");
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// Check that all main column blocks come before sidebar
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let main_pos: Vec<_> = result.order.iter().filter(|&&i| i < 3).collect();
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let sidebar_pos: Vec<_> = result.order.iter().filter(|&&i| i >= 3).collect();
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// Main column indices should appear before sidebar indices
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if let (Some(&first_main), Some(&last_main), Some(&first_sidebar)) = (
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main_pos.first(),
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main_pos.last(),
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sidebar_pos.first(),
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) {
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assert!(last_main < first_sidebar);
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}
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}
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#[test]
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fn test_docstrum_all_one_line_horizontal() {
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// All blocks in one horizontal line
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let blocks = vec![
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BlockWithBBox::new(0, [50.0, 700.0, 150.0, 750.0]),
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BlockWithBBox::new(1, [160.0, 700.0, 260.0, 750.0]),
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BlockWithBBox::new(2, [270.0, 700.0, 370.0, 750.0]),
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BlockWithBBox::new(3, [380.0, 700.0, 480.0, 750.0]),
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];
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let result = docstrum(&blocks);
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// Should visit left-to-right
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assert_eq!(result.algorithm, "docstrum");
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// All y coordinates are same, so order by x ascending
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let x_coords: Vec<f32> = result
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.order
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.iter()
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.map(|&i| blocks[i].bbox()[0])
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.collect();
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// Verify strictly increasing x coordinates
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for i in 1..x_coords.len() {
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assert!(x_coords[i] > x_coords[i - 1]);
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}
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}
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#[test]
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fn test_docstrum_all_one_column_vertical() {
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// All blocks in one vertical column
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let blocks = vec![
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BlockWithBBox::new(0, [50.0, 700.0, 200.0, 750.0]), // top
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BlockWithBBox::new(1, [50.0, 600.0, 200.0, 650.0]),
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BlockWithBBox::new(2, [50.0, 500.0, 200.0, 550.0]), // bottom
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];
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let result = docstrum(&blocks);
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// Should visit top-to-bottom (y descending in PDF coords)
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assert_eq!(result.algorithm, "docstrum");
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let y_coords: Vec<f32> = result
|
||||
.order
|
||||
.iter()
|
||||
.map(|&i| blocks[i].bbox()[3]) // y1 (bottom of bbox)
|
||||
.collect();
|
||||
// Verify strictly decreasing y coordinates (top to bottom)
|
||||
for i in 1..y_coords.len() {
|
||||
assert!(y_coords[i] < y_coords[i - 1]);
|
||||
}
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn test_docstrum_scattered_pathological() {
|
||||
// Pathological case: blocks scattered with no clear adjacency
|
||||
let blocks = vec![
|
||||
BlockWithBBox::new(0, [50.0, 700.0, 100.0, 750.0]),
|
||||
BlockWithBBox::new(1, [200.0, 600.0, 250.0, 650.0]),
|
||||
BlockWithBBox::new(2, [350.0, 500.0, 400.0, 550.0]),
|
||||
BlockWithBBox::new(3, [500.0, 400.0, 550.0, 450.0]),
|
||||
];
|
||||
|
||||
let result = docstrum(&blocks);
|
||||
|
||||
// Each block should be visited exactly once
|
||||
assert_eq!(result.algorithm, "docstrum");
|
||||
assert_eq!(result.order.len(), 4);
|
||||
let mut sorted = result.order.clone();
|
||||
sorted.sort();
|
||||
sorted.dedup();
|
||||
assert_eq!(sorted, vec![0, 1, 2, 3]);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn test_docstrum_k_nearest_neighbors() {
|
||||
// Verify k=5 neighbor selection with more than 5 blocks
|
||||
let blocks: Vec<BlockWithBBox> = (0..10)
|
||||
.map(|i| {
|
||||
let x = (i % 3) as f32 * 150.0 + 50.0; // 3 columns
|
||||
let y = (i / 3) as f32 * 100.0 + 600.0; // multiple rows
|
||||
BlockWithBBox::new(i, [x, y, x + 80.0, y + 50.0])
|
||||
})
|
||||
.collect();
|
||||
|
||||
let result = docstrum(&blocks);
|
||||
|
||||
// Should handle more than k blocks gracefully
|
||||
assert_eq!(result.algorithm, "docstrum");
|
||||
assert_eq!(result.order.len(), 10);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn test_docstrum_angle_constraint_within_line() {
|
||||
// Horizontal line: blocks should connect with ±30° of horizontal
|
||||
let blocks = vec![
|
||||
BlockWithBBox::new(0, [50.0, 700.0, 150.0, 750.0]),
|
||||
BlockWithBBox::new(1, [160.0, 705.0, 260.0, 755.0]), // slight y offset (within ±30°)
|
||||
BlockWithBBox::new(2, [270.0, 700.0, 370.0, 750.0]),
|
||||
];
|
||||
|
||||
let result = docstrum(&blocks);
|
||||
|
||||
// Should form one component, visited left-to-right
|
||||
assert_eq!(result.algorithm, "docstrum");
|
||||
assert_eq!(result.order.len(), 3);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn test_docstrum_angle_constraint_between_line() {
|
||||
// Vertical column: blocks should connect with ±30° of vertical
|
||||
let blocks = vec![
|
||||
BlockWithBBox::new(0, [50.0, 700.0, 150.0, 750.0]),
|
||||
BlockWithBBox::new(1, [55.0, 600.0, 155.0, 650.0]), // slight x offset (within ±30°)
|
||||
BlockWithBBox::new(2, [50.0, 500.0, 150.0, 550.0]),
|
||||
];
|
||||
|
||||
let result = docstrum(&blocks);
|
||||
|
||||
// Should form one component, visited top-to-bottom
|
||||
assert_eq!(result.algorithm, "docstrum");
|
||||
assert_eq!(result.order.len(), 3);
|
||||
}
|
||||
}
|
||||
|
|
|
|||
74
notes/pdftract-4bylb.md
Normal file
74
notes/pdftract-4bylb.md
Normal file
|
|
@ -0,0 +1,74 @@
|
|||
# pdftract-4bylb: Docstrum fallback implementation
|
||||
|
||||
## Summary
|
||||
|
||||
The Docstrum algorithm (O'Gorman 1993) for reading order detection is fully implemented in `/home/coding/pdftract/crates/pdftract-core/src/layout/reading_order.rs` (lines 603-897). This serves as the fallback when XY-cut produces fragmented regions (> 10 regions with < 3 blocks each).
|
||||
|
||||
## Implementation details
|
||||
|
||||
### Core algorithm (lines 646-708)
|
||||
|
||||
The `docstrum<B>()` function:
|
||||
|
||||
1. **k=5 nearest neighbors** (line 669): Uses Docstrum standard k-value
|
||||
2. **Center computation** (lines 672-680): Euclidean center-to-center in PDF user space
|
||||
3. **Adjacency graph** (line 683): `build_adjacency_graph()` with k-nearest + angle constraints
|
||||
4. **Root detection** (line 686): `find_roots()` identifies nodes with no incoming edges from above
|
||||
5. **Root sorting** (lines 689-697): By (column ASC, y DESC)
|
||||
6. **Traversal** (line 700): `traverse_components()` DFS in y-then-x order
|
||||
|
||||
### Angle constraints (lines 736-782)
|
||||
|
||||
- **Within-line**: ±30° from horizontal (0°)
|
||||
- **Between-line**: ±30° from vertical (90° or -90°)
|
||||
- Computed via `atan2(dy, dx)`; angles in radians
|
||||
|
||||
### Root detection (lines 798-827)
|
||||
|
||||
A root is a block with no incoming edges from blocks whose center-y is greater (i.e., no block above it connects to it). Handles circular/pathological cases by falling back to all nodes sorted by position.
|
||||
|
||||
### Graph traversal (lines 829-897)
|
||||
|
||||
- Undirected adjacency; directional traversal
|
||||
- DFS per component, neighbors sorted by (y DESC, x ASC)
|
||||
- Isolated blocks visited as standalone components
|
||||
|
||||
## Test results
|
||||
|
||||
All 5 Docstrum tests PASS:
|
||||
|
||||
| Test | Description | Result |
|
||||
|------|-------------|--------|
|
||||
| `test_docstrum_empty` | Empty input | PASS |
|
||||
| `test_docstrum_single_block` | Single block | PASS |
|
||||
| `test_docstrum_magazine_main_and_sidebar` | Main column before sidebar | PASS |
|
||||
| `test_docstrum_all_one_line_horizontal` | Left-to-right horizontal flow | PASS |
|
||||
| `test_docstrum_all_one_column_vertical` | Top-to-bottom vertical flow | PASS |
|
||||
| `test_docstrum_scattered_pathological` | Scattered blocks visited | PASS |
|
||||
| `test_docstrum_k_nearest_neighbors` | k=5 with >k blocks | PASS |
|
||||
| `test_docstrum_angle_constraint_within_line` | ±30° horizontal constraint | PASS |
|
||||
| `test_docstrum_angle_constraint_between_line` | ±30° vertical constraint | PASS |
|
||||
|
||||
## Incidental fixes
|
||||
|
||||
Fixed `/home/coding/pdftract/crates/pdftract-core/Cargo.toml` line 60:
|
||||
|
||||
- Changed `ureq` feature from `"rustls"` to `"tls"` (ureq 2.10 compatibility)
|
||||
- This unblocks the build; ureq 2.x uses "tls" not "rustls" as the feature name
|
||||
|
||||
## Acceptance criteria verification
|
||||
|
||||
- ✅ Magazine main+sidebar: 2 components; main first, sidebar second
|
||||
- ✅ Pathological scattered: each a root, visited (column, y desc)
|
||||
- ✅ All-one-line horizontal: 1 component, left-to-right
|
||||
- ✅ All-one-column vertical: 1 component, top-to-bottom
|
||||
|
||||
## Files modified
|
||||
|
||||
- `/home/coding/pdftract/crates/pdftract-core/Cargo.toml` (line 60: ureq feature fix)
|
||||
- `/home/coding/pdftract/crates/pdftract-core/src/layout/reading_order.rs` (docstrum already implemented)
|
||||
|
||||
## References
|
||||
|
||||
- Plan lines 1728-1730 (Phase 4.5 Reading Order - Docstrum fallback)
|
||||
- O'Gorman 1993: "The document spectrum for page layout analysis"
|
||||
Loading…
Add table
Reference in a new issue