GIS常用npm包：GeoJSON文件合并与元素过滤\属性过滤\图形合并

GeoJSON文件合并

普通的geoJSON文件合并，只需geojson-merge插件就够了，https://www.npmjs.com/package/@mapbox/geojson-merge

mergeFeatureCollectionStream 合并文件

Merge GeoJSON files containing GeoJSON FeatureCollections into a single stream of a FeatureCollection as a JSON string.
merge 合并GeoJSON数组

Merge a series of GeoJSON objects into one FeatureCollection containing all features in all files. The objects can be any valid GeoJSON root object, including FeatureCollection, Feature, and Geometry types.

合并文件，官网的案例

var geojsonMerge = require('@mapbox/geojson-merge'); 
var mergedStream = geojsonMerge.mergeFeatureCollectionStream(['features.geojson','others.geojson']) 
mergedStream.pipe(process.stdout);

在浏览器端，需要导入文件，fileReader读取文件，获取json，再合并

var geojsonMerge = require('@mapbox/geojson-merge')
let features = []
// Todo push jgeoJSON
let jsonObject = geojsonMerge.merge(features)

GeoJSON过滤

GeoJSON一feature properties过滤

https://www.npmjs.com/package/turf-filter

turf.filter(features, key, value)

var features = turf.featurecollection([
 turf.point([-72.581777, 44.260875], {species: 'oak'}),
 turf.point([-72.570018, 44.260691], {species: 'birch'}),
 turf.point([-72.576284, 44.257925], {species: 'oak'}),
 turf.point([-72.56916, 44.254605], {species: 'redwood'}),
 turf.point([-72.581691, 44.24858], {species: 'maple'}),
 turf.point([-72.583837, 44.255773], {species: 'oak'})
]);
 
var key = 'species';
var value = 'oak';
  
var filtered = turf.filter(features, key, value);

这个过滤比较简单，https://www.npmjs.com/package/feature-filter-geojson

可以增加过滤规则，具体还是看官方文档。在浏览器端，其实用第一个就好

var ff = require('feature-filter');
var filter = [
    "all",
    ["==", "class", "street_limited"],
    ["<=", "admin_level", 3],
    ["!=", "$type", "Polygon"]
]
var testFilter = ff(filter);
let feature = GeoJSONObject
testFilter(feature);

https://www.npmjs.com/package/geojson-filter,这个也是一样的，但是推荐用第一个

geojson-dissolve

GeoJSON 里面的点线面合并为Multi(point/linestring/polygon)

Dissolve contiguous GeoJSON (Multi)LineStrings and (Multi)Polygons into single units.

说实话，这个实际项目，我目前还没有用到。

merge polygon 合并多边形

merge-simple-polygons：https://www.npmjs.com/package/merge-simple-polygons

Merge two (adjacent) simple polygons into another simple polygon.

Takes two arrays of vertex IDs, each spanning a planar polygon and returns:

false if the given polygons share no vertices
null if there would be more than one resulting simple polygon (if the two given polygons share either exactly one vertex, which would result in two polygons or multiple egdes that are not connected, which would result in a polygon with a "hole")
a list of vertex IDs forming the merged polygon

const mergePolygons = require('merge-simple-polygons')
  
const polygonA = ['a', 'b', 'c', 'd', 'e']
const polygonB = ['e', 'a', 'g', 'h', 'i', 'd']
const polygonC = mergePolygons(polygonA, polygonB)
console.log(polygonC) // ['a', 'b', 'c', 'd', 'i', 'h', 'g']
  
const polygonD = ['a', 'b', 'c']
const polygonE = ['d', 'e', 'f']
console.log(mergePolygons(polygonD, polygonE)) // false
  
const polygonF = ['a', 'b', 'c', 'd', 'e']
const polygonG = ['a', 'b', 'f', 'e', 'd', 'g']
console.log(mergePolygons(polygonF, polygonG)) // null