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);