GEE APP：利用夜间灯光数据建立一个简易的逐年影像查看器

news2024/9/21 7:59:34

简介

很多时候我们可以通过简单的滑块进行逐年影像的查看，slider这个工具可以进行每一年的夜间灯光数据的查看，这里主需要设定其实和后续的年份，另外，并给每一年进行属性设定对应的影像即可。这里最关键的就是一个返回值函数的设定，也就是滑块中的onchange函数的设定，这里我们首先要初始化地图界面，然后设定每一年份的属性。

函数

ee.Date.fromYMD(year, month, day, timeZone)

Returns a Date given year, month, day.

Arguments:

year (Integer):

The year, 2013, for example.

month (Integer):

The month, 3, for example.

day (Integer):

The day, 15, for example.

timeZone (String, default: null):

The time zone (e.g., 'America/Los_Angeles'); defaults to UTC.

Returns: Date

ee.DateRange(start, end, timeZone)

Creates a DateRange with the given start (inclusive) and end (exclusive), which may be Dates, numbers (interpreted as milliseconds since 1970-01-01T00:00:00Z), or strings (such as '1996-01-01T08:00'). If 'end' is not specified, a 1-millisecond range starting at 'start' is created.

创建具有给定开始（包括）和结束（不包括）的Date Range，这些开始可能是日期、数字（解释为自1970-01- 01 T00：00 Z以来的毫秒）或字符串（例如“1996-01- 01 T08：00”）。如果未指定“end”，则会创建从“start”开始的1毫秒范围。

Arguments:

start (Object)

end (Object, default: null)

timeZone (String, default: null):

If start and/or end are provided as strings, the time zone in which to interpret them; defaults to UTC.

Returns: DateRange

ui.Slider(min, max, value, step, onChange, direction, disabled, style)

A draggable target that ranges linearly between two numeric values. The value of the slider is displayed as a label alongside it.

Arguments:

min (Number, optional):

The minimum value. Defaults to 0.

max (Number, optional):

The maximum value. Defaults to 1.

value (Number, optional):

The initial value. Defaults to 0.

step (Number, optional):

The step size for the slider. Defaults to 0.01.

onChange (Function, optional):

A callback to fire when the slider's state changes. The callback is passed the slider's current value and the slider widget.

direction (String, optional):

The direction of the slider. One of

'horizontal' or 'vertical'. Defaults to 'horizontal'.

disabled (Boolean, optional):

Whether the slider is disabled. Defaults to false.

style (Object, optional):

An object of allowed CSS styles with their values to be set for this widget. See style() documentation.

Returns: ui.Slider

代码

/*
收藏幻灯片
通过使用滑动块选择显示层来可视化集合中的更改 
*/

var roi = 
    /* color: #d63000 */
    /* displayProperties: [
      {
        "type": "rectangle"
      }
    ] */
    ee.Geometry.Polygon(
        [[[30.077489497329147, -28.41003324023103],
          [30.077489497329147, -28.718802987087276],
          [30.635045649672897, -28.718802987087276],
          [30.635045649672897, -28.41003324023103]]], null, false);

// 从带有silder的收藏中选择图像。 

var collection = ee.ImageCollection('NOAA/DMSP-OLS/NIGHTTIME_LIGHTS')
    .select('stable_lights')

// 一个帮助器函数，用于在默认地图上显示给定年份的图像。 
var showLayer = function(year) {
  Map.layers().reset();
  var date = ee.Date.fromYMD(year, 1, 1);
  var dateRange = ee.DateRange(date, date.advance(1, 'year'));
  var image = collection.filterDate(dateRange).first();
  Map.addLayer({
    eeObject: ee.Image(image),
    visParams: {
      min: 0,
      max: 63,
      palette:['000000', 'FFFF00', 'FFA500', 'FF4500', 'FF0000']
    },
    name: String(year)
  });
};

// 创建标签和属性
var label = ui.Label('Light Intensity for Year');
var slider = ui.Slider({
  min: 1992,
  max: 2014,
  step: 1,
  onChange: showLayer,
  style: {stretch: 'horizontal'}
});

// 创建一个包含滑动块和标签的面板。
var panel = ui.Panel({
  widgets: [label, slider],
  layout: ui.Panel.Layout.flow('vertical'),
  style: {
    position: 'top-center',
    padding: '7px'
  }
});

// 添加面板
Map.add(panel);

// 设定默认的滑块和年份设定地图中心店
slider.setValue(2007);
Map.setCenter(30, 45, 4);