Stop Adding Sliders for Local Errors: The Case for Spatial Overrides

TLDR

When document processing engines misclassify a region on a specific page, developers frequently respond by adding another global threshold slider. This pattern leads to "slider hunting": tweaking global parameters to fix page 3 damages page 7. Global sliders are the wrong abstraction for local structural errors. Replacing threshold tuning with a direct canvas manipulation layer, allowing users to select, resize, reclassify, or split regions locally, solves layout errors permanently without side effects.

Correction Abstraction	Error Scope	Maintenance Overhead	Long-Term Stability
Global Threshold Sliders	Global (Applies to all pages)	High (Continuous threshold tuning)	Fragile (Tuning causes regressions)
Direct Spatial Overrides	Local (Target page/region only)	Zero (Isolated region edits)	100% Deterministic & Stable

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Problem statement: the myth of the perfect threshold set

In document analysis tools, developers often expose global threshold sliders:

• R_Y_BAND (Line grouping tolerance)
• R_PARA_GAP (Paragraph separation gap)
• R_COL_GAP_MIN (Minimum column gutter width)

When a table on page 3 extracts incorrectly, users adjust R_COL_GAP_MIN from 12px to 18px.

Page 3 extracts cleanly. But on page 7, two closely-spaced prose columns now merge into a single garbled block because 18px is too wide for page 7's layout.

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Technical failure mode: abstract global controls for concrete local errors

Global thresholds assume document layout rules are uniform across all pages.

In reality, documents contain local structural anomalies (a tight table next to wide prose, an indented block quote, a floating diagram).

Attempting to model local anomalies using global numeric sliders creates an endless cycle of threshold adjustments and regressions.

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The fix: local spatial overrides

Keep global thresholds stable, and provide an interactive canvas editing layer for local overrides:

[Automatic Pipeline Pass] ---> [Interactive Canvas Editor] ---> [Local Spatial Override Map] ---> [Assembly Engine]

Local override map representation

Store local overrides as explicit bounding box overrides rather than modifying global parameters:

// Local Page Overrides Map
export const pageOverridesStore = {
  // Keyed by page number; contains only local spatial overrides
  3: {
    manualSplits: [{ x: 456.5 }], // Forced vertical column split at X=456.5px
    customRegions: [
      {
        id: 'user_override_p3_r1',
        type: 'LATTICE_TABLE',     // Forced classification override
        bbox: { x: 54, y: 120, w: 500, h: 320 },
        algorithm: 'manual-override'
      }
    ],
    skipRegions: new Set(['p3_auto_region_4']) // Suppress false-positive auto region
  }
};

When re-processing page 3, the assembly engine merges local overrides directly over automated proposals, leaving all other pages completely untouched.

Rule of thumb: Never expose global threshold sliders to solve local structural layout errors. Build direct spatial canvas override tools instead.