基于 geojson数据类型面转线Transforms Polygons and MultiPolygons to LineStrings.

function flatten(array) {
return [].concat.apply([], array);
}

function polygonToLineString(coordinates, properties) {
return coordinates.map(function(coordinates) {
return turf.lineString(coordinates, properties);
});
}

function multiPolygonToLineString(coordinates, properties) {
return flatten(coordinates.map(function(coordinates) {
return polygonToLineString(coordinates, properties);
}));
}

function toLineString(feature) {
var geometry = feature.geometry,
properties = feature.properties;

switch (geometry.type) {
case 'Polygon':
return polygonToLineString(geometry.coordinates, properties);
case 'MultiPolygon':
return multiPolygonToLineString(geometry.coordinates, properties);
default:
return feature;
}
}
/**
* Transforms Polygons and MultiPolygons to LineStrings.
*
* @module turf/polygonToLine
* @category transformation
* @param {Object} geojson any GeoJSON object
* @returns {Object} FeatureCollection where
* Polygons and MultiPolygons transformed to LineStrings.
*/
function polygon2line(geojson) {
var features = geojson.features.map(toLineString);
return turf.featureCollection(flatten(features));
}