GEE学习笔记 八十六：分类中的特征重要性分析_gee随机森林特征重要性变成0到1

之前在GEE中做随机森林分类时候，很多人都在问如何做特征重要性分析？但是在GEE之前并没有相关API可以做特征重要性分析，最新的API更新后GEE也可以做特征重要性分析了。

1、目前常用的包含特征重要信息分析的分类方法包括：

（1）决策树

ee.Classifier.smileCart(maxNodes, minLeafPopulation)

（2）随机森林

ee.Classifier.smileRandomForest(numberOfTrees, variablesPerSplit, minLeafPopulation, bagFraction, maxNodes, seed)

    这两个方法和之前的分类决策树和随机森林分类方法参数非常类似，只不过调用这两个定义方法在使用explain()方法就可以得到每个分类特征重要性的信息。

2、得到特征重要性的API方法：

 

    也就是之前在分类器中的方法explain，这个方法是最开始就有的，只不过是最近GEE官方加入了特征重要性的分析返回信息，下面通过一个具体例子说明一下如何使用以及具体输出。

具体代码：

1. var roi =

3.     /* color: #d63000 */

5.     /* shown: false */

7.     /* displayProperties: [

9.       {

11.         "type": "rectangle"

13.       }

15.     ] */

17.     ee.Geometry.Polygon(

19.         [[[114.23790821489501, 36.43657462800738],

21.           [114.23790821489501, 36.29834769127675],

23.           [114.49265369829345, 36.29834769127675],

25.           [114.49265369829345, 36.43657462800738]]], null, false),

27.     crop =

29.     /* color: #98ff00 */

31.     /* shown: false */

33.     ee.FeatureCollection(

35.         [ee.Feature(

37.             ee.Geometry.Point([114.31343922075439, 36.356156419842804]),

39.             {

41.               "type": 0,

43.               "system:index": "0"

45.             }),

47.         ee.Feature(

49.             ee.Geometry.Point([114.31056389269042, 36.35499859187555]),

51.             {

53.               "type": 0,

55.               "system:index": "1"

57.             }),

59.         ee.Feature(

61.             ee.Geometry.Point([114.31236633714843, 36.3529248270982]),

63.             {

65.               "type": 0,

67.               "system:index": "2"

69.             }),

71.         ee.Feature(

73.             ee.Geometry.Point([114.32159313615966, 36.35461840580203]),

75.             {

77.               "type": 0,

79.               "system:index": "3"

81.             }),

83.         ee.Feature(

85.             ee.Geometry.Point([114.32348141130615, 36.35638107103549]),

87.             {

89.               "type": 0,

91.               "system:index": "4"

93.             }),

95.         ee.Feature(

97.             ee.Geometry.Point([114.32936081346679, 36.35589720612248]),

99.             {

101.               "type": 0,

103.               "system:index": "5"

105.             }),

107.         ee.Feature(

109.             ee.Geometry.Point([114.33515438493896, 36.35565527253804]),

111.             {

113.               "type": 0,

115.               "system:index": "6"

117.             }),

119.         ee.Feature(

121.             ee.Geometry.Point([114.33545479234863, 36.35855842592195]),

123.             {

125.               "type": 0,

127.               "system:index": "7"

129.             }),

131.         ee.Feature(

133.             ee.Geometry.Point([114.29468521532226, 36.35679580999553]),

135.             {

137.               "type": 0,

139.               "system:index": "8"

141.             }),

143.         ee.Feature(

145.             ee.Geometry.Point([114.29979214128662, 36.34922647614173]),

147.             {

149.               "type": 0,

151.               "system:index": "9"

153.             }),

155.         ee.Feature(

157.             ee.Geometry.Point([114.28871998247314, 36.3387180531404]),

159.             {

161.               "type": 0,

163.               "system:index": "10"

165.             }),

167.         ee.Feature(

169.             ee.Geometry.Point([114.28279766496826, 36.33833778756726]),

171.             {

173.               "type": 0,

175.               "system:index": "11"

177.             }),

179.         ee.Feature(

181.             ee.Geometry.Point([114.39553627428222, 36.3299369018726]),

183.             {

185.               "type": 0,

187.               "system:index": "12"

189.             }),

191.         ee.Feature(

193.             ee.Geometry.Point([114.39725288805175, 36.32997147527504]),

195.             {

197.               "type": 0,

199.               "system:index": "13"

201.             }),

203.         ee.Feature(

205.             ee.Geometry.Point([114.39712414201904, 36.32796619257241]),

207.             {

209.               "type": 0,

211.               "system:index": "14"

213.             }),

215.         ee.Feature(

217.             ee.Geometry.Point([114.39918407854248, 36.3291762831369]),

219.             {

221.               "type": 0,

223.               "system:index": "15"

225.             }),

227.         ee.Feature(

229.             ee.Geometry.Point([114.39845451769042, 36.3274475765775]),

231.             {

233.               "type": 0,

235.               "system:index": "16"

237.             }),

239.         ee.Feature(

241.             ee.Geometry.Point([114.40467724260498, 36.32900341420687]),

243.             {

245.               "type": 0,

247.               "system:index": "17"

249.             }),

251.         ee.Feature(

253.             ee.Geometry.Point([114.40480598863769, 36.32734385296429]),

255.             {

257.               "type": 0,

259.               "system:index": "18"

261.             }),

263.         ee.Feature(

265.             ee.Geometry.Point([114.38210377153564, 36.33612529650057]),

267.             {

269.               "type": 0,

271.               "system:index": "19"

273.             }),

275.         ee.Feature(

277.             ee.Geometry.Point([114.38034424242187, 36.336194437797644]),

279.             {

281.               "type": 0,

283.               "system:index": "20"

285.             }),

287.         ee.Feature(

289.             ee.Geometry.Point([114.38098797258544, 36.34041194086619]),

291.             {

293.               "type": 0,

295.               "system:index": "21"

297.             }),

299.         ee.Feature(

301.             ee.Geometry.Point([114.38785442766357, 36.337473540724005]),

303.             {

305.               "type": 0,

307.               "system:index": "22"

309.             }),

311.         ee.Feature(

313.             ee.Geometry.Point([114.38532242235351, 36.34227863160822]),

315.             {

317.               "type": 0,

319.               "system:index": "23"

321.             })]),

323.     nocrop =

325.     /* color: #0b4a8b */

327.     /* shown: false */

329.     ee.FeatureCollection(

331.         [ee.Feature(

333.             ee.Geometry.Point([114.36832794603515, 36.344663782445146]),

335.             {

337.               "type": 1,

339.               "system:index": "0"

341.             }),

343.         ee.Feature(

345.             ee.Geometry.Point([114.37463650163818, 36.345078583829164]),

347.             {

349.               "type": 1,

351.               "system:index": "1"

353.             }),

355.         ee.Feature(

357.             ee.Geometry.Point([114.37742599901367, 36.34576991455905]),

359.             {

361.               "type": 1,

363.               "system:index": "2"

365.             }),

367.         ee.Feature(

369.             ee.Geometry.Point([114.378026813833, 36.34860430638123]),

371.             {

373.               "type": 1,

375.               "system:index": "3"

377.             }),

379.         ee.Feature(

381.             ee.Geometry.Point([114.37386402544189, 36.35009059256129]),

383.             {

385.               "type": 1,

387.               "system:index": "4"

389.             }),

391.         ee.Feature(

393.             ee.Geometry.Point([114.36987289842773, 36.352198996374725]),

395.             {

397.               "type": 1,

399.               "system:index": "5"

401.             }),

403.         ee.Feature(

405.             ee.Geometry.Point([114.37695393022705, 36.351887923993054]),

407.             {

409.               "type": 1,

411.               "system:index": "6"

413.             }),

415.         ee.Feature(

417.             ee.Geometry.Point([114.3797005122583, 36.35392715363849]),

419.             {

421.               "type": 1,

423.               "system:index": "7"

425.             }),

427.         ee.Feature(

429.             ee.Geometry.Point([114.37352070268798, 36.35627738595022]),

431.             {

433.               "type": 1,

435.               "system:index": "8"

437.             }),

439.         ee.Feature(

441.             ee.Geometry.Point([114.31785950121093, 36.34438724696162]),

443.             {

445.               "type": 1,

447.               "system:index": "9"

449.             }),

451.         ee.Feature(

453.             ee.Geometry.Point([114.31657204088378, 36.34345393245458]),

455.             {

457.               "type": 1,

459.               "system:index": "10"

461.             }),

463.         ee.Feature(

465.             ee.Geometry.Point([114.34390911516357, 36.33512274079625]),

467.             {

469.               "type": 1,

471.               "system:index": "11"

473.             }),

475.         ee.Feature(

477.             ee.Geometry.Point([114.35094723161865, 36.33723154988948]),

479.             {

481.               "type": 1,

483.               "system:index": "12"

485.             }),

487.         ee.Feature(

489.             ee.Geometry.Point([114.35309299883056, 36.337058698833104]),

491.             {

493.               "type": 1,

495.               "system:index": "13"

497.             }),

499.         ee.Feature(

501.             ee.Geometry.Point([114.35296425279785, 36.33501902740074]),

503.             {

505.               "type": 1,

507.               "system:index": "14"

509.             }),

511.         ee.Feature(

513.             ee.Geometry.Point([114.41952058729305, 36.35091929703152]),

515.             {

517.               "type": 1,

519.               "system:index": "15"

521.             }),

523.         ee.Feature(

525.             ee.Geometry.Point([114.41966006216182, 36.3516321782695]),

527.             {

529.               "type": 1,

531.               "system:index": "16"

533.             }),

535.         ee.Feature(

537.             ee.Geometry.Point([114.41982099470272, 36.35252219053154]),

539.             {

541.               "type": 1,

543.               "system:index": "17"

545.             }),

547.         ee.Feature(

549.             ee.Geometry.Point([114.42009458002224, 36.35383558809808]),

551.             {

553.               "type": 1,

555.               "system:index": "18"

557.             }),

559.         ee.Feature(

561.             ee.Geometry.Point([114.42027697023525, 36.35499343336394]),

563.             {

565.               "type": 1,

567.               "system:index": "19"

569.             }),

571.         ee.Feature(

573.             ee.Geometry.Point([114.42028233465328, 36.35609509850472]),

575.             {

577.               "type": 1,

579.               "system:index": "20"

581.             }),

583.         ee.Feature(

585.             ee.Geometry.Point([114.42228326257839, 36.35603461533285]),

587.             {

589.               "type": 1,

591.               "system:index": "21"

593.             }),

595.         ee.Feature(

597.             ee.Geometry.Point([114.42357072290554, 36.35606053669799]),

599.             {

601.               "type": 1,

603.               "system:index": "22"

605.             })]),

607.     water =

609.     /* color: #ffc82d */

611.     /* shown: false */

613.     ee.FeatureCollection(

615.         [ee.Feature(

617.             ee.Geometry.Point([114.3321717685144, 36.3306024371752]),

619.             {

621.               "type": 2,

623.               "system:index": "0"

625.             }),

627.         ee.Feature(

629.             ee.Geometry.Point([114.33210739549804, 36.333592954210076]),

631.             {

633.               "type": 2,

635.               "system:index": "1"

637.             }),

639.         ee.Feature(

641.             ee.Geometry.Point([114.28854832109619, 36.41266166922327]),

643.             {

645.               "type": 2,

647.               "system:index": "2"

649.             }),

651.         ee.Feature(

653.             ee.Geometry.Point([114.29610142168212, 36.40879346635716]),

655.             {

657.               "type": 2,

659.               "system:index": "3"

661.             }),

663.         ee.Feature(

665.             ee.Geometry.Point([114.28580173906494, 36.40547771059803]),

667.             {

669.               "type": 2,

671.               "system:index": "4"

673.             }),

675.         ee.Feature(

677.             ee.Geometry.Point([114.29541477617431, 36.40160915003326]),

679.             {

681.               "type": 2,

683.               "system:index": "5"

685.             }),

687.         ee.Feature(

689.             ee.Geometry.Point([114.3057144587915, 36.40547771059803]),

691.             {

693.               "type": 2,

695.               "system:index": "6"

697.             }),

699.         ee.Feature(

701.             ee.Geometry.Point([114.29953464922119, 36.39829308768715]),

703.             {

705.               "type": 2,

707.               "system:index": "7"

709.             }),

711.         ee.Feature(

713.             ee.Geometry.Point([114.39435610231533, 36.3617846267207]),

715.             {

717.               "type": 2,

719.               "system:index": "8"

721.             }),

723.         ee.Feature(

725.             ee.Geometry.Point([114.39429172929897, 36.361179837099506]),

727.             {

729.               "type": 2,

731.               "system:index": "9"

733.             }),

735.         ee.Feature(

737.             ee.Geometry.Point([114.38845524248256, 36.35940000037548]),

739.             {

741.               "type": 2,

743.               "system:index": "10"

745.             }),

747.         ee.Feature(

749.             ee.Geometry.Point([114.38152441438808, 36.35701530096524]),

751.             {

753.               "type": 2,

755.               "system:index": "11"

757.             }),

759.         ee.Feature(

761.             ee.Geometry.Point([114.38133129533901, 36.35653143999478]),

763.             {

765.               "type": 2,

767.               "system:index": "12"

769.             }),

771.         ee.Feature(

773.             ee.Geometry.Point([114.39965614732876, 36.36371992192421]),

775.             {

777.               "type": 2,

779.               "system:index": "13"

781.             }),

783.         ee.Feature(

785.             ee.Geometry.Point([114.40693029817714, 36.3668473954689]),

787.             {

789.               "type": 2,

791.               "system:index": "14"

793.             }),

795.         ee.Feature(

797.             ee.Geometry.Point([114.41094288286342, 36.36890351124372]),

799.             {

801.               "type": 2,

803.               "system:index": "15"

805.             }),

807.         ee.Feature(

809.             ee.Geometry.Point([114.40238127168789, 36.36840244602017]),

811.             {

813.               "type": 2,

815.               "system:index": "16"

817.             })]);

821. //监督分类

823. Map.centerObject(roi, 11);

825. Map.addLayer(roi, {color: "red"}, "roi", false);

827. var sampleData = crop.merge(nocrop).merge(water);

831. //Landsat8 SR数据去云

833. function rmCloud(image) {

835.   var cloudShadowBitMask = (1 << 3);

837.   var cloudsBitMask = (1 << 5);

839.   var qa = image.select("pixel_qa");

841.   var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0)

843.                  .and(qa.bitwiseAnd(cloudsBitMask).eq(0));

845.   return image.updateMask(mask);

847. }

851. //缩放

853. function scaleImage(image) {

855.   var time_start = image.get("system:time_start");

857.   image = image.multiply(0.0001);

859.   image = image.set("system:time_start", time_start);

861.   return image;

863. }

867. //NDVI

869. function NDVI(image) {

871.   return image.addBands(

873.     image.normalizedDifference(["B5", "B4"])

875.          .rename("NDVI"));

877. }

879. //NDWI

881. function NDWI(image) {

883.   return image.addBands(

885.     image.normalizedDifference(["B3", "B5"])

887.          .rename("NDWI"));

889. }

891. //NDBI

893. function NDBI(image) {

895.   return image.addBands(

897.     image.normalizedDifference(["B6", "B5"])

899.          .rename("NDBI"));

901. }

903. var l8Col = ee.ImageCollection("LANDSAT/LC08/C01/T1_SR")

905.               .filterBounds(roi)

907.               .filterDate("2018-1-1", "2019-1-1")

909.               .map(rmCloud)

911.               .map(scaleImage)

913.               .map(NDVI)

915.               .map(NDWI)

917.               .map(NDBI);

919. var bands = [

921.   "B1", "B2", "B3", "B4", "B5", "B6", "B7",

923.   "NDBI", "NDWI", "NDVI"

925. ];

927. var l8Image = l8Col.median()

929.                    .clip(roi)

931.                    .select(bands);

933. var rgbVisParam = {

935.   min: 0,

937.   max: 0.3,

939.   bands: ["B4", "B3", "B2"]

941. };

943. Map.addLayer(l8Image, rgbVisParam, "l8Image");

945. //生成监督分类训练使用的样本数据

947. var training = l8Image.sampleRegions({

949.   collection: sampleData,

951.   properties: ["type"],

953.   scale: 30

955. });

957. //初始化分类器

959. // var classifier = ee.Classifier.smileCart().train({

961. //   features: training,

963. //   classProperty: "type",

965. //   inputProperties: bands

967. // });

969. var classifier = ee.Classifier.smileRandomForest(10).train({

971.   features: training,

973.   classProperty: "type",

975.   inputProperties: bands

977. });

979. print(classifier.explain());

982. //影像数据调用classify利用训练数据训练得到分类结果

984. var classified = l8Image.classify(classifier);

986. //训练结果的混淆矩阵

988. var trainAccuracy = classifier.confusionMatrix();

990. Map.addLayer(classified, {min:0, max:2, palette: ["green", "orange", "blue"]}, "classify");

代码分析：

（1）这段代码做的是一个简单的监督分类，通过自己标注的样本将影像分成3大类（作物、非作物和水），样本由于是我做测试随机标注的，所以测试精度和分类准确度不高。

（2）和之前的分类代码相比较，这里只是更换了分类方法，比如随机森林我使用的是smileRandomForest方法，参数和之前的方法的参数类似，这里只是简单设置了树的个数为10。

（3）然后对分类器调用explain方法就可以查看特征重要性信息，输出结果如下面所示。

运行结果：

    比如使用ee.Classifier.smileRandomForest()方法做的分类结果，使用explain后的信息如下图：

来源请引用：地理遥感生态网科学数据注册与出版系统。