fosteev / Leaflet.PolylineDecorator

A plug-in for the JS map library Leaflet, allowing to define patterns (like dashes, arrows, icons, etc.) on Polylines.

Leaflet PolylineDecorator

A Leaflet plug-in to define and draw patterns on existing Polylines or along coordinate paths. Demo.

Compatibility with Leaflet versions

The current version of the plugin (on the master branch) works only with versions 1.* of Leaflet.

For a version of the plugin compatible with the older 0.7.* Leaflet releases, use the leaflet-0.7.2 branch. But this branch is not maintained anymore and Leaflet 1.* has been around for a while, so you should definitely update.

npm / bower

npm install leaflet-polylinedecorator

bower install leaflet-polylinedecorator

Features

• Dashed or dotted lines, arrow heads, markers following line
• Works on Polygons too! (easy, as Polygon extends Polyline)
• Multiple patterns can be applied to the same line
• New behaviors can be obtained by defining new symbols

Screenshot

Usage

To create a decorator and add it to the map: L.polylineDecorator(latlngs, options).addTo(map);

• latlngs can be one of the following types:

• L.Polyline

• L.Polygon

• an array of L.LatLng, or with Leaflet's simplified syntax, an array of 2-cells arrays of coordinates (useful if you just want to draw patterns following coordinates, but not the line itself)

• an array of any of these previous types, to apply the same patterns to multiple lines

• options has a single property patterns, which is an array of Pattern objects.

Pattern definition

Property	Type	Required	Description
offset	see below	No	Offset of the first pattern symbol, from the start point of the line. Default: 0.
endOffset	see below	No	Minimum offset of the last pattern symbol, from the end point of the line. Default: 0.
repeat	see below	Yes	Repetition interval of the pattern symbols. Defines the distance between each consecutive symbol's anchor point.
symbol	Symbol factory	Yes	Instance of a symbol factory class.

offset, endOffset and repeat can be each defined as a number, in pixels, or in percentage of the line's length, as a string (ex: '10%').

Methods

Method	Description
setPaths(latlngs)	Changes the path(s) the decorator applies to. latlngs can be all the types supported by the constructor. Useful for example if you remove polyline from a set, or coordinates change.
setPatterns(<Pattern[]> patterns)	Changes the decorator's pattern definitions, and update the symbols accordingly.

Example

var polyline = L.polyline([...]).addTo(map);
var decorator = L.polylineDecorator(polyline, {
    patterns: [
        // defines a pattern of 10px-wide dashes, repeated every 20px on the line
        {offset: 0, repeat: 20, symbol: L.Symbol.dash({pixelSize: 10})}
    ]
}).addTo(map);

Performance note/alternatives

This plugin creates actual L.Layer objects (markers, polyline, etc.) to draw the pattern symbols. This is extra customizable as you can define your own symbols, but it may have an impact on the responsiveness of your map if you have to draw a lot of symbols on many large polylines.

Here are two light-weight alternatives for simpler cases:

• the dashArray property of L.Path, if you only need to draw simple patterns (dashes, dots, etc.).
• the Leaflet.TextPath plugin, which is based on SVG.