GPXFIT

Shrink

The Shrink tool reduces the number of track points in your file while preserving the overall shape of the route. Choose between two simplification methods.

When to Use

This tool is useful when:

  • Your file is too large and you need to reduce its size
  • You have an overly detailed track that's slow to load
  • You want to simplify a route for sharing
  • Your GPS recorded at very high frequency and you need fewer points

How to Use

  1. Upload your GPX or FIT file
  2. Click the Shrink button to open the tool
  3. Choose a simplification method:
- Every Nth Point - Simple percentage-based reduction - Douglas-Peucker - Intelligent shape-preserving algorithm
  1. Adjust the slider for your chosen method
  2. Watch the preview update in real-time
  3. Click Apply when satisfied with the result

Simplification Methods

Every Nth Point (Percentage)

This method evenly removes points at regular intervals:

  • How it works: Keeps a percentage of points, evenly distributed along the track
  • Best for: Quick reduction when exact shape preservation isn't critical
  • Slider: 5% to 100% of points to keep

For example, if you have 1000 points and select 50%:

  • 500 points will be kept
  • First and last points are preserved
  • 498 intermediate points are evenly spaced

Douglas-Peucker Algorithm

This is an intelligent simplification algorithm that preserves the shape of your route by keeping points that matter most:

  • How it works: Recursively removes points that deviate less than the tolerance from a simplified line
  • Best for: Maximum reduction while maintaining route accuracy
  • Slider: 1m (fine detail) to 100m (coarse simplification)

The algorithm:

  1. Draws a line from the first to last point
  2. Finds the point with the greatest perpendicular distance from this line
  3. If that distance exceeds the tolerance, keeps the point and recursively processes both halves
  4. Removes all points within the tolerance

Why use Douglas-Peucker?

  • Keeps more points on curves and turns where detail matters
  • Removes more points on straight sections where they're redundant
  • Produces smaller files with better shape fidelity than simple decimation

Preview

The tool shows:

  • Route preview - See how the simplified route looks
  • Elevation chart - Watch how the elevation profile changes
  • Point count - Original and reduced point counts with reduction percentage

Considerations

What's Affected

  • Number of track points (reduced)
  • File size (smaller)
  • Route detail (lower resolution)

What's Preserved

  • Start and end points (always kept)
  • Overall route shape (especially with Douglas-Peucker)
  • Elevation data (for kept points)
  • Timestamps (for kept points)
  • Sensor data (for kept points)
  • Segment boundaries (processed separately)

Tips

  • Try Douglas-Peucker first - It usually gives better results with greater reduction
  • Start with 5-10m tolerance - A good balance between size and accuracy
  • Check elevation - The elevation chart shows how detail is affected
  • Consider use case - Navigation needs fewer points than detailed analysis
  • Test the result - Download and verify before deleting the original

Tolerance Guide (Douglas-Peucker)

Tolerance Use Case
1-2m High precision, minimal reduction
5-10m Good balance for most uses
20-50m Significant reduction, still recognizable
50-100m Maximum compression, overview only

File Size Impact

Reducing points has a significant impact on file size:

Reduction Typical Size Change
50% fewer points ~45-50% smaller
75% fewer points ~70-75% smaller
90% fewer points ~85-90% smaller
Actual results vary based on the original file's metadata and extensions.