C34 建筑环境（Part 7）

导读：

建筑环境由环境的人为物理部分组成，包括房屋、建筑物、街道、开放空间和基础设施。

重点分析全球基础设施数据集。

主要内容：

量化道路特征。
理解基于矢量和基于栅格的方法。

Section 1 GEE目前可用的数据集

the Global Power Plant Database
Open Buildings V1 Polygons (whichcurrently includes over half of Africa)
Global Artificial Impervious Area
the Global Flood Database
the Global Roads Inventory Project
(GRIP) dataset
。。。。

Section 2 道路特征

使用Global Roads Inventory Project (GRIP) 数据集计算道路长度。

该数据集旨在为环境和生物多样性评估（environmental and biodiversity assessments）提供一致的全球道路数据集。

//=======================================================================================
// 导入非洲、南美洲和欧洲的道路数据
var grip4_africa = ee.FeatureCollection( 'projects/sat-io/open-datasets/GRIP4/Africa'), 
    grip4_north_america = ee.FeatureCollection( 'projects/sat-io/open-datasets/GRIP4/North-America'), 
    grip4_europe = ee.FeatureCollection( 'projects/sat-io/open-datasets/GRIP4/Europe'); 
     
     
// print('Grip4 Africa size', grip4_africa.size()); 
// print('Grip4 North America size', grip4_north_america.size()); 
// print('Grip4 Europe size', grip4_europe.size()); 
 
 
// // 显示道路数据. 
// Map.addLayer(ee.FeatureCollection(grip4_africa).style({ 
//     color: '413B3A', 
//     width: 1
// }), {}, 'Grip4 Africa'); 
 
// Map.addLayer(ee.FeatureCollection(grip4_north_america).style({ 
//     color: '413B3A', 
//     width: 1
// }), {}, 'Grip4 North America'); 
 
// Map.addLayer(ee.FeatureCollection(grip4_europe).style({ 
//     color: '413B3A', 
//     width: 1
// }), {}, 'Grip4 Europe'); 
 
 
//==========================================================================================
// 导入国家边界数据，计算国家面积，选择一个面积最大的国家
var countries = ee.FeatureCollection('USDOS/LSIB_SIMPLE/2017'); 
// Add a function to calculate the feature's geometry area. 
// Add the function as a property. 
var addArea = function(feature) { 
    return feature.set({ 
        areaKm: feature.geometry().area().divide(1000 * 1000) 
    }); // km2 squared 
}; 
 
// Map the area getting function over the FeatureCollection. 
var countriesArea = countries.map(addArea); 
print("countriesArea", countriesArea);
 
// Filter to the largest country in Africa . 
var Algeria = countriesArea.filter(ee.Filter.inList('country_na', [ 'Algeria' ])); 
 
// Display the selected countries.阿尔及利亚 
Map.addLayer(Algeria.style({ 
    fillColor: 'b5ffb4', 
    color: '00909F', 
    width: 1.0
}), {}, 'Algeria'); 
 
//=============================================================================================
 
//定义函数:为相关的GRIP数据集计算每个国家的道路长度。
var roadLength4Country = function(country, grip4) { 
   
    // Join roads to countries. 
    var intersectsFilter = ee.Filter.intersects({ 
        leftField: '.geo', 
        rightField: '.geo', 
        maxError: 10
    }); 
 
    var grip4Selected = grip4.filterBounds(country); 
 
    var countriesWithRds = ee.Join.saveAll('roads').apply({ 
        primary: country, 
        secondary: grip4Selected, 
        condition: intersectsFilter 
    }).filter(ee.Filter.neq('roads', null)); 
     
    // Return country with calculation of roadLength and roadsPerArea. 
    return countriesWithRds.map(function(country) { 
        var roadsList = ee.List(country.get('roads')); 
        var roadLengths = roadsList.map(function(road) { 
            return ee.Feature(road).intersection( country, 10).length(10); 
        }); 
         
        var roadLength = ee.Number(roadLengths.reduce(ee .Reducer.sum())); 
        return country.set({ 
            roadLength: roadLength.divide( 1000), // Convert to km. 
            roadsPerArea: roadLength.divide(ee .Number(country.get('areaKm')) 
            ) 
        }); 
    }).select(['country_na', 'areaKm', 'roadLength', 
       'roadsPerArea'
    ]); 
}; 
 
// Apply the road length function to Algeria. 
var roadLengthAlgeria = roadLength4Country(Algeria, grip4_africa);
 
 
// Print the road statistics for Algeria. 
print('Roads statistics in Algeria', roadLengthAlgeria); 