flot-downsample: Downsample plugin for Flot

• Author: Sveinn Steinarsson
• Special thanks: Borgar Þorsteinsson and DataMarket

This plugin for Flot charts downsamples data before rendering the chart. The purpose is to try retain the visual characteristics of the original line using considerably fewer data points. The algorithm (called Largest-Triangle-Three-Buckets or LTTB) used in this plugin is described in a Master's thesis (see hdl.handle.net/1946/15343) in Computer Science by Sveinn Steinarsson at the University of Iceland. The topic of the thesis is how to downsample time series for visual representation and was initially suggested by DataMarket. JavaScript optimization was done with the help of Borgar Þorsteinsson.

Demo

Demo can viewed at flot.base.is.

Additional demo concerning chart resizing is also available at flot.base.is/demo-resize

Usage

series: {
  downsample: {
    threshold: 1000 // 0 disables downsampling for this series.
  }
}

Known limitations

• Does not support gaps (null values) in the data array.
• X-values must be in a strictly increasing order.

Articles about the algorithm (LTTB)

• The Challenge of Metrics Visualization by Mark Troyer
• Downsampling data – Not a trivial task by DataMarket

The algorithm (LTTB) adapted for other programming languages or frameworks

• C# by Daniel Judge
• node.js by Matej Drolc
• Java by drcrane
• Scala by Graham Tackley
• R by Jack Viljoen
• Javascript (without the flot plugin) by Josh Carr
• Highcarts Plugin by Sveinn Steinarsson
• PHP by dbojdo

Note: I have not tested all these versions and some might have different or additional features.

(Please let me know if you make your own port of the LTTB algorithm so I can list it here.)

License

flot-downsample is released under the terms of the MIT License.