【Google Earth Engine编程语言学习笔记】Geometry、Feature、FeatureCollection

一、【Geometry】形状

（1）创建

1.创建点ee.Geometry.Point()　　创建多点ee.Geometry.MultiPoint()

• var ct=ee.Geometry.Point(116.3968,39.9186)
  Map.centerObject(ct)
  print(ct)
  Map.addLayer(ct)

2.创建线ee.Geometry.LineString([[x1,y1],[x2,y2],[x3,y3]])　　

   创建多线ee.Geometry.MultiLineString([[[x1,y1],[x2,y2],[x3,y3]],[[x4,y4],[x5,y5]],])

3.创建闭合线ee.Geometry.LinearRing([[x1,y1],[x2,y2],[x3,y3],[x1,y1]])

   创建多闭合线ee.Geometry.MultiLineString()

4.创建面ee.Geometry.Polygon([[x1,y1],[x2,y2],[x3,y3],[x4,y4]])

   ee.Geometry.Polygon([[[x1,y1],[x2,y2],[x3,y3],[x4,y4]],[[x5,y5],[x6,y6],[x7,y7],[x8,y8]]])后一个在前一个里边，变成中空的多边形

• var ct=ee.Geometry.Polygon([
  [[116.38307485597535,39.915666765209366],
  [116.39178667085572,39.915666765209366],
  [116.39178667085572,39.92142675789876],
  [116.38307485597535,39.92142675789876]],
  
  [ [116.38595018403932,39.91744418606569],
  [116.38946924226686,39.91744418606569],
  [116.38946924226686,39.919517785427374],
  [116.38595018403932,39.919517785427374]]
  ])
  Map.centerObject(ct)
  print(ct)
  Map.addLayer(ct)

 ee.Geometry.MultiPolygon(定义每个多边形的顶点)

ee.Geometry.Rectangle(两个对顶点的坐标)

（2）几何

1.Geometry.transform()

这一部分转换我理解的也不太明白，主要就是投影转换

• var China_Geo = ee.Geometry.Rectangle(65.9, 19.8,134.5, 50.9);
  var China_Planr = ee.Geometry(China_Geo, null, false);
  var China_Plnar_2 = China_Geo.transform('EPSG:4326', ee.ErrorMargin(100))
  Map.addLayer(China_Geo, {color: 'FF0000'}, 'geodesic polygon')//投影坐标
  Map.addLayer(China_Planr,{color: '000000'}, 'planar polygon')//平面直角坐标
  Map.addLayer(China_Plnar_2,{color: '0000CD'}, 'planar polygon')//转换为投影坐标

 

具体的查看https://epsg.io

2.Geometry.centroid()求几何形状的中心点

3.Geometry.simplify()对某个引入的图形进行简化

• var m=ee.FeatureCollection("路径").geometry();

  var m_sim=m.simplify(简化的尺度)尺度越大越不简单

4.Geometry.bounds()

   Geometry.convexHull()

5.Geometry.buffer()缓冲区

6.Geometry.union()联合　　Geometry.intersection()相交　　difference求反

（3）查询

1.Geometry.geometries()将多面分解为单面　　

2.Geometry.coordinate()求坐标

3.Geometry.area求面积　　

4.Geometry.perimeter求周长　　

5.Geometry.diatance求两个多边形最近的距离

（4）转换

Geometry.toGeoJSON()将图形的格式转换，转换为GeoJSON格式在转化为shp格式就不会乱码

二、【feature】

feature和geometry在空间上表述是一样的，但是feature比geometry包含更多的信息量，如geometry代表地图中某个省份的行政边界，feature不仅包含行政边界，还包括他的属性信息，如人口，GDP等

（1）创建

ee.Feature(空间信息，属性信息（dictionary类型）)创建一个要素

• var ct=ee.Geometry.Polygon([
  [116.38307485597535,39.915666765209366],
  [116.39178667085572,39.915666765209366],
  [116.39178667085572,39.92142675789876],
  [116.38307485597535,39.92142675789876]
  ])
  var ct_fea=ee.Feature(ct,{name:'ww',location:'bj'})
  Map.centerObject(ct)
  print(ct_fea)
  Map.addLayer(ct_fea)

 

但是最简单绘制feature的方法为

 

将会在代码区自动生成代码

 

修改属性

 

（2）编辑

1.select(选择属性, newProperties, retainGeometry)

如创建一个feature，当执行select命令时，只保留选择的属性字段，类似于复制

• var ct=ee.Geometry.Polygon([
  [116.38307485597535,39.915666765209366],
  [116.39178667085572,39.915666765209366],
  [116.39178667085572,39.92142675789876],
  [116.38307485597535,39.92142675789876]
  ])
  var ct_fea=ee.Feature(ct,{name:'ww',location:'bj'})
  var ct_fea_sel=ct_fea.select(['name'])
  Map.centerObject(ct)
  print(ct_fea)
  Map.addLayer(ct_fea)

• ct_fea_sel=ct_fea.select(['name'],['名称'])

 

 2.transform(proj, maxError)

与geometry一样，将某种坐标系转换为另一种坐标系

3.set(var_args)   

对相关的属性信息进行重写或覆盖

• var ct=ee.Geometry.Polygon([
  [116.38307485597535,39.915666765209366],
  [116.39178667085572,39.915666765209366],
  [116.39178667085572,39.92142675789876],
  [116.38307485597535,39.92142675789876]
  ])
  var ct_fea=ee.Feature(ct,{name:'ww',location:'bj'})
  var ct_set=ct_fea.set('name','wwww','location','bbjj')
  print(ct_fea,ct_set)
  Map.centerObject(ct)
  Map.addLayer(ct_fea)

 

 4.setMulti(properties)对多个变量进行修改

注意：括号里边跟的的字典形式

• var ct_set=ct_fea.setMulti({'name':'wwww','location':'bbjj'})

（3）几何

与geometry一样也可以对feature进行同样的操作

centroid（质心）/simplify（简化）/bounds（边界）/convexHull（边）/buffer（缓冲区）

 union()联合　　intersection()相交　　difference求差

（4）提取

geometry将feature的属性信息剥离只剩下属性信息

get(属性字段)获取该属性字段的属性值

area/perimeter获得面积和周长

三、【FeatureCollection】

即feature的集合

（1）创建

1.GEE自带

在搜索框中输入‘table’>点击‘more’

2.上传

 

 

 

3.ee.FeatureCollection()

首先建立不同的特征，如point、line、polygon，然后将这些特征通过ee.FeatureCollection([point,line,polygon])集合起来，

Feature和FeatureCollection的关系，类似于arcgis中的要素和要素集，或者supermap中的数据集和数据源

4.FeatureCollection.randomPoints(生成点的范围，生成的点数) 创建随机点

前提条件是要确定生成点的范围

5.手绘，方法类似于feature

（2）编辑

1.FeatureCollection.filterMetadata()依据属性值筛选

• var coun = ee.FeatureCollection("users/wangchengcong/HB");
  var coun_hb=coun.filterMetadata('NAME','equals','唐山')//选择NAME为唐山的地区
  Map.centerObject(coun_hb)
  Map.addLayer(coun,{color:'FFFF00'});
  Map.addLayer(coun_hb,{color:'FF0000'});

2.FeatureCollection.limit()依据限制大小筛选

• var coun_china=coun.limit(筛选多少个量，要依据哪个属性字段来筛选，正序还是倒序)

 

3.FeatureCollection.filterDate()依据时间筛选

• var landsat_filterDate=imageCollection.filterDate('起始时间'，‘终止时间’).limit(筛选个数)

4.FeatureCollection.filterBounds()依据空间位置筛选

• var coun = ee.FeatureCollection("users/wangchengcong/HB");
  var point=ee.Geometry.Point([118.2914,39.8459]);
  var ts=coun.filterBounds(point)

  Map.centerObject(coun)
  Map.addLayer(coun);
  Map.addLayer(ts,{color:'FF0000'});

5.FeatureCollection.filter()

是上述筛选的总称

FeatureCollection.select()同feature中的选择

FeatureCollection.distinct(['属性字段'])去除重复字段

FeatureCollection.union()合并，没有边界，原来的属性全部丧失

FeatureCollection.merge()融合。有边界

FeatureCollection.set()同feature中的set

FeatureCollection.remap()是对某一栏目下的属性进行批量重新命名操作

• var China_Provinces=ee.FeatureCollection("users/wangjinzhulala/China_Provinces");
  var Old_Provinces_lD=ee.List([1,2,3,4,5,6,7,8,9,12,13,14,15,16,18,19,20,21,22,23,24,27,28,29,30,31,32,33,34,35,36,37,38,39,1089])
  var New_Provinces_lD=ee.List([1,1,1,1,2,2,2,2,2,3,3,3,3,3,4,4,4,4,4,4,5,5,5,5,5,6,6,6,6,6,7,7,7,7,7])
  var China_Remap = China_Provinces.remap(Old_Provinces_lD,New_Provinces_lD,'OBJECTID')
  var China_Provinces_Map =China_Provinces.reduceTolmage(['OBJECTID'], ee.Reducer.first())
  var China_Remap_Map = China_Provinces.reduceTolmage(['OBJECTID'], ee.Reducer.first())
  Map.centerObject(China_Provinces,4)
  Map.addLayer(China_Provinces_Map,{min:1, max:40, palette:'16ff07,2901ff'},'China_Provinces_Map')
  Map.addLayer(China_Remap_Map,{min:1, max:7, palette:'ff7248,fbff21,09ffe8'},'China_Remap_Map')

FeatureCollection.sort()对原来的属性表进行排序

FeatureCollection.makeArray()将一些选中的属性信息弄成array

（3）转换

FeatureCollection.geometry()获取geometry信息

FeatureCollection.reduceTolmage(['属性字段',ee.Reducer])矢量转栅格

（4）查询

FeatureCollection.first()只选取第一个

FeatureCollection.toList()将某个属性字段变成list，好处就是可以提取任意位置的feature

• var list=china_province.sort('属性字段'，正序倒序).toList(10)//排序选取前10个

  var no1=ee.Feature(list.get(1))获取第二个值

FeatureCollection.aggregate_ first()某一列的第一个值

FeatureCollection.aggregate_ array()某一列排序

（5） 统计

FeatureCollection.aggregate_ stats属性表最大最小值等/_ histogram直方图数值/_ count/_ count _distinct

FeatureCollection.aggregate. _max/_ min/, sum/_ _mean/_ product

FeatureCollection.aggregate_ sample_var/_ total _var/, sample_ sd/_ total _sd/

（6）其他

FeatureCollection.map()对每个元素进行同样的操作

• var HB=ee.FeatureCollection("users/wangchengcong/HB");
  function add(fea)
  {
  return fea.centroid()
  }
  var center=HB.map(add)

  Map.centerObject(HB,4)
  Map.addLayer(HB)
  Map.addLayer(center,{color:'FF0000'})