使用表格生成要素集

主要功能

使用在线数据筛选生成要素集

代码

// Create a FeatureCollection from a Fusion Table.

// Select "desert" features from the TNC Ecoregions fusion table.
var fc = ee.FeatureCollection('ft:1Ec8IWsP8asxN-ywSqgXWMuBaxI6pPaeh6hC64lA')
  .filter(ee.Filter.stringContains('ECO_NAME', 'desert'));

// Paint into a blank image.  Cast to byte() so we can use more than 1 color.
var image1 = ee.Image().byte().paint(fc, 'ECO_NUM');

// Display the image using random colors for each value.
Map.setCenter(-109.687, 30.524, 5);
Map.addLayer(image1.randomVisualizer());

步骤分析

1. 使用在线数据，筛选字段属性
2. 将筛选出的要素输出到一个数据对象中
3. 设置地图中心，缩放等级
4. 添加图层，展示结果

主要方法

1. ee.FeatureCollection()
   FeatureCollections can be constructed from the following arguments:

• A string: assumed to be the name of a collection.
• A single geometry.
• A single feature.
• A list of features.
• A computed object: reinterpreted as a collection.
  Arguments:
  args (ComputedObject|Feature|FeatureCollection|Geometry|List<Object>|Number|String):
  The constructor arguments.
  column (String, optional):
  The name of the geometry column to use. Only useful with constructor type 1.
  Returns: FeatureCollection

创建要素集。

2. ee.Filter.stringContains()
   Creates a unary or binary filter that passes if the left operand, a string, contains the right operand, also a string.
   Arguments:
   leftField (String, default: null):
   A selector for the left operand. Should not be specified if leftValue is specified.
   rightValue (Object, default: null):
   The value of the right operand. Should not be specified if rightField is specified.
   rightField (String, default: null):
   A selector for the right operand. Should not be specified if rightValue is specified.
   leftValue (Object, default: null):
   The value of the left operand. Should not be specified if leftField is specified.
   Returns: Filter

过滤器，判断是否包含特定字符串。
输入参数：左属性（字符串），右值，右属性（字符串），左值

3. ee.Image.paint()
   Paints the geometries of a collection onto an image.
   Arguments:
   this:image (Image):
   The image on which the collection is painted.
   featureCollection (FeatureCollection):
   The collection painted onto the image.
   color (Object, default: 0):
   Either the name of a color property or a number.
   width (Object, default: null):
   Either the name of a line-width property or a number.
   Returns: Image

将地理几何要素输出到为影像数据。
输入参数：影像（输出结果），要素集，颜色，宽度

4. ee.Image.randomVisualizer()
   Creates a vizualization image by assigning a random color to each unique value of the pixels of the first band. The first three bands of the output image will contan 8-bit R, G and B values, followed by all bands of the input image.
   Arguments:
   this:image (Image):
   Image with at least one band.
   Returns: Image

对影像数据的第一波段中的不同值赋予随机颜色输出彩色图像，输出结果为8位RGB影像
输入参数：影像对象（需至少包含一个波段）