【Google Earth Engine編程語言學習筆記】Geometry、Feature、FeatureCollection

一、【Geometry】形狀

（1）創建

1.創建點ee.Geometry.Point()　　創建多點ee.Geometry.MultiPoint()

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

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

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

3.創建閉合線ee.Geometry.LinearRing([[x1,y1],[x2,y2],[x3,y3],[x1,y1]])

   創建多閉合線ee.Geometry.MultiLineString()

4.創建面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]]])后一個在前一個里邊，變成中空的多邊形

• 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(定義每個多邊形的頂點)

ee.Geometry.Rectangle(兩個對頂點的坐標)

（2）幾何

1.Geometry.transform()

這一部分轉換我理解的也不太明白，主要就是投影轉換

• 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')//投影坐標
  Map.addLayer(China_Planr,{color: '000000'}, 'planar polygon')//平面直角坐標
  Map.addLayer(China_Plnar_2,{color: '0000CD'}, 'planar polygon')//轉換為投影坐標

 

具體的查看https://epsg.io

2.Geometry.centroid()求幾何形狀的中心點

3.Geometry.simplify()對某個引入的圖形進行簡化

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

  var m_sim=m.simplify(簡化的尺度)尺度越大越不簡單

4.Geometry.bounds()

   Geometry.convexHull()

5.Geometry.buffer()緩沖區

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

（3）查詢

1.Geometry.geometries()將多面分解為單面　　

2.Geometry.coordinate()求坐標

3.Geometry.area求面積　　

4.Geometry.perimeter求周長　　

5.Geometry.diatance求兩個多邊形最近的距離

（4）轉換

Geometry.toGeoJSON()將圖形的格式轉換，轉換為GeoJSON格式在轉化為shp格式就不會亂碼

二、【feature】

feature和geometry在空間上表述是一樣的，但是feature比geometry包含更多的信息量，如geometry代表地圖中某個省份的行政邊界，feature不僅包含行政邊界，還包括他的屬性信息，如人口，GDP等

（1）創建

ee.Feature(空間信息，屬性信息（dictionary類型）)創建一個要素

• 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)

 

但是最簡單繪制feature的方法為

 

將會在代碼區自動生成代碼

 

修改屬性

 

（2）編輯

1.select(選擇屬性, newProperties, retainGeometry)

如創建一個feature，當執行select命令時，只保留選擇的屬性字段，類似於復制

• 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'],['名稱'])

 

 2.transform(proj, maxError)

與geometry一樣，將某種坐標系轉換為另一種坐標系

3.set(var_args)   

對相關的屬性信息進行重寫或覆蓋

• 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)對多個變量進行修改

注意：括號里邊跟的的字典形式

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

（3）幾何

與geometry一樣也可以對feature進行同樣的操作

centroid（質心）/simplify（簡化）/bounds（邊界）/convexHull（邊）/buffer（緩沖區）

 union()聯合　　intersection()相交　　difference求差

（4）提取

geometry將feature的屬性信息剝離只剩下屬性信息

get(屬性字段)獲取該屬性字段的屬性值

area/perimeter獲得面積和周長

三、【FeatureCollection】

即feature的集合

（1）創建

1.GEE自帶

在搜索框中輸入‘table’>點擊‘more’

2.上傳

 

 

 

3.ee.FeatureCollection()

首先建立不同的特征，如point、line、polygon，然后將這些特征通過ee.FeatureCollection([point,line,polygon])集合起來，

Feature和FeatureCollection的關系，類似於arcgis中的要素和要素集，或者supermap中的數據集和數據源

4.FeatureCollection.randomPoints(生成點的范圍，生成的點數) 創建隨機點

前提條件是要確定生成點的范圍

5.手繪，方法類似於feature

（2）編輯

1.FeatureCollection.filterMetadata()依據屬性值篩選

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

2.FeatureCollection.limit()依據限制大小篩選

• var coun_china=coun.limit(篩選多少個量，要依據哪個屬性字段來篩選，正序還是倒序)

 

3.FeatureCollection.filterDate()依據時間篩選

• var landsat_filterDate=imageCollection.filterDate('起始時間'，‘終止時間’).limit(篩選個數)

4.FeatureCollection.filterBounds()依據空間位置篩選

• 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()

是上述篩選的總稱

FeatureCollection.select()同feature中的選擇

FeatureCollection.distinct(['屬性字段'])去除重復字段

FeatureCollection.union()合並，沒有邊界，原來的屬性全部喪失

FeatureCollection.merge()融合。有邊界

FeatureCollection.set()同feature中的set

FeatureCollection.remap()是對某一欄目下的屬性進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()對原來的屬性表進行排序

FeatureCollection.makeArray()將一些選中的屬性信息弄成array

（3）轉換

FeatureCollection.geometry()獲取geometry信息

FeatureCollection.reduceTolmage(['屬性字段',ee.Reducer])矢量轉柵格

（4）查詢

FeatureCollection.first()只選取第一個

FeatureCollection.toList()將某個屬性字段變成list，好處就是可以提取任意位置的feature

• var list=china_province.sort('屬性字段'，正序倒序).toList(10)//排序選取前10個

  var no1=ee.Feature(list.get(1))獲取第二個值

FeatureCollection.aggregate_ first()某一列的第一個值

FeatureCollection.aggregate_ array()某一列排序

（5） 統計

FeatureCollection.aggregate_ stats屬性表最大最小值等/_ histogram直方圖數值/_ 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()對每個元素進行同樣的操作

• 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'})