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8000 GitHub - TBusan/d3-contour: Compute contour polygons using marching squares.
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Optimized d3-contour

An optimized version of the d3-contour library with improved performance, topology handling, edge clipping, and smoothing controls.

Key Improvements

  1. Performance Optimization

    • Added a spatial index for faster hole-polygon assignment
    • Replaced Array with Map for fragment tracking
    • Added bounds checking for early rejection in point-in-polygon tests
    • Optimized point-in-polygon algorithm
  2. Topology Correctness

    • Implemented level-by-level contour processing to ensure topological consistency
    • Added post-processing to remove overlaps between different contour levels
    • Ensured unique attribution of areas to contour levels
  3. Edge Clipping

    • Added proper edge clipping at grid boundaries
    • Preserved valid rings while discarding invalid ones after clipping
  4. Enhanced Smoothing Control

    • Added a smoothFactor parameter to control the degree of smoothing
    • Preserved existing smooth/no-smooth option

New API Methods

Contours

d3.co
83B2
ntours()
    .size([width, height])
    .thresholds(thresholdValues)
    .smoothFactor(1.0)  // New: Control smoothing intensity (default: 1.0)
    .clipEdges(true)    // New: Enable/disable edge clipping (default: true)

ContourDensity

d3.contourDensity()
    .x(x)
    .y(y)
    .size([width, height])
    .cellSize(cellSize)
    .thresholds(thresholdValues)
    .bandwidth(bandwidth)
    .smoothFactor(1.0)  // New: Control smoothing intensity (default: 1.0)
    .clipEdges(true)    // New: Enable/disable edge clipping (default: true)

Usage Example

// Create contours with enhanced controls
const contours = d3.contours()
    .size([width, height])
    .thresholds(10)  // 10 contour levels
    .smoothFactor(0.8)  // Slightly reduced smoothing
    .clipEdges(true);  // Enable edge clipping

// Apply to data
const contourData = contours(values);

// Visualize
svg.selectAll("path")
    .data(contourData)
    .enter().append("path")
    .attr("d", d3.geoPath())
    .attr("fill", d => color(d.value));

Technical Details

The optimizations focus on addressing key issues in the original implementation:

  1. Spatial Indexing: Replaced O(n²) comparisons for hole assignments with a more efficient spatial index.

  2. Topological Consistency: Implemented a level-by-level processing approach to ensure proper nesting relationships between contour levels.

  3. Edge Cases: Added proper handling of grid edge cases with the new clipping functionality.

  4. Memory Efficiency: Used Map objects for better performance with large datasets.

  5. Numerical Stability: Improved collinearity tests for point-on-segment checks with a small epsilon value.

Integration

This optimized library is a drop-in replacement for the original d3-contour library, with full compatibility with existing code while providing new optional features through additional parameters.

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Compute contour polygons using marching squares.

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