我正在编写一个小应用程序。我有以下数据
{
"feat": [
{
"type": "Feature",
"id": "AFG",
"properties": {
"name": "Afghanistan"
},
"geometry": {
"type": "Polygon",
"coordinates": [
[
[
61.210817,
35.650072
],
[
64.546479,
36.312073
],
[
64.746105,
37.111818
],
[
65.588948,
37.305217
],
[
65.745631,
37.661164
],
[
66.217385,
37.39379
],
[
66.518607,
37.362784
],
[
67.075782,
37.356144
],
[
67.83,
37.144994
],
[
68.135562,
37.023115
],
[
68.859446,
37.344336
],
[
69.196273,
37.151144
],
[
69.518785,
37.608997
],
[
70.116578,
37.588223
],
[
70.270574,
37.735165
],
[
71.262348,
36.074388
],
[
71.498768,
35.650563
],
[
71.613076,
35.153203
],
[
71.115019,
34.733126
],
[
71.156773,
34.348911
],
[
70.881803,
33.988856
],
[
69.930543,
34.02012
],
[
70.323594,
33.358533
],
[
69.687147,
33.105499
],
[
69.262522,
32.501944
],
[
69.317764,
31.901412
],
[
68.926677,
31.620189
],
[
68.556932,
31.71331
],
[
67.792689,
31.58293
],
[
60.52843,
33.676446
],
[
60.803193,
34.404102
],
[
61.210817,
35.650072
]
]
]
}
},
{
"type": "Feature",
"id": "AGO",
"properties": {
"name": "Angola"
},
"geometry": {
"type": "MultiPolygon",
"coordinates": [
[
[
[
16.326528,
-5.87747
],
[
16.57318,
-6.622645
],
[
16.860191,
-7.222298
],
[
17.089996,
-7.545689
],
[
17.47297,
-8.068551
],
[
21.801801,
-8.908707
],
[
21.875182,
-9.523708
],
[
22.208753,
-9.894796
],
[
22.155268,
-11.084801
],
[
22.402798,
-10.993075
],
[
22.837345,
-11.017622
],
[
23.456791,
-10.867863
],
[
23.912215,
-10.926826
],
[
24.017894,
-11.237298
],
[
23.904154,
-11.722282
],
[
24.079905,
-12.191297
],
[
23.930922,
-12.565848
],
[
24.016137,
-12.911046
],
[
21.933886,
-12.898437
],
[
21.887843,
-16.08031
],
[
22.562478,
-16.898451
],
[
23.215048,
-17.523116
],
[
21.377176,
-17.930636
],
[
18.956187,
-17.789095
],
[
18.263309,
-17.309951
],
[
12.175619,
-14.449144
],
[
12.500095,
-13.5477
],
[
12.738479,
-13.137906
],
[
13.312914,
-12.48363
],
[
13.633721,
-12.038645
],
[
13.738728,
-11.297863
],
[
13.686379,
-10.731076
],
[
13.387328,
-10.373578
],
[
13.120988,
-9.766897
],
[
12.87537,
-9.166934
],
[
13.375597,
-5.864241
],
[
16.326528,
-5.87747
]
]
],
[
[
[
12.436688,
-5.684304
],
[
12.182337,
-5.789931
]
]
]
]
}
},
{
"type": "Feature",
"id": "ALB",
"properties": {
"name": "Albania"
},
"geometry": {
"type": "Polygon",
"coordinates": [
[
[
20.590247,
41.855404
],
[
19.406082,
40.250773
],
[
19.319059,
40.72723
],
[
19.40355,
41.409566
],
[
19.540027,
41.719986
],
[
19.371769,
41.877548
],
[
19.304486,
42.195745
],
[
19.738051,
42.688247
],
[
19.801613,
42.500093
],
[
20.0707,
42.58863
],
[
20.283755,
42.32026
],
[
20.52295,
42.21787
],
[
20.590247,
41.855404
]
]
]
}
}
]
}
发生的情况是用户将提供纬度和经度。然后我需要查找这些值是否存在于上面的数据集中。如果是，则返回该国家/地区。
问题是上面的数据集坐标数组不同。有时是 3 维，有时是 2 维。它在不断变化。我不确定如何找到有效的解决方案。
下面是我的一些代码，目前它提示用户输入纬度和经度并循环数据。
const rl = require('readline').createInterface(process.stdin, process.stdout);
const coordinates = require('./data.json').feat;
var prompts = ['Enter coordinates (lat, lon)'],
counter = 0;
// console.log(countries);
rl.on('line', (line) => {
if (!line) {
console.log('Enter values.');
}
let lat = line.split(' ')[0],
lon = line.split(' ')[1];
console.log(lat, lon);
coordinates.forEach((data, index) => {
console.log(data.geometry.coordinates[index]);
data.geometry.coordinates.forEach((geo, i) => {
// console.log(geo[i]);
});
});
get();
}).on('close', () => {
});
function get() {
rl.setPrompt(prompts[counter] + ': ');
rl.prompt();
}
get();
在上述数据集中查找给定的经度和纬度有什么帮助吗？
最佳答案
您可以通过检查type属性来检测多边形的数量。如果是 MultiPolygon，您将多一层嵌套级别。
以下是一些可用于确定点是否位于多边形中的函数。代码片段的其余部分(下部)允许测试 getCountry 函数:它执行 map 绘制、鼠标移动处理并显示鼠标移动过的国家/地区。但本质就在最上面的三个函数。
这是普通的 JS，基于 this article 中提供的缠绕算法，但您可能需要考虑使用库来代替，例如 d3.js 。
function isLeft(p0, p1, p2) {
return ( (p1[0] - p0[0]) * (p2[1] - p0[1])
- (p2[0] - p0[0]) * (p1[1] - p0[1]) );
}
function inPoly(p, coord) {
var winding = 0;
// loop through all edges of the polygon
for (var i=0; i<coord.length-1; i++) {
if (coord[i][1] <= p[1]) {
if (coord[i+1][1] > p[1]) // an upward crossing
if (isLeft(coord[i], coord[i+1], p) > 0) // p left of edge
++winding; // have a valid up intersect
} else { // start y > P.y (no test needed)
if (coord[i+1][1] <= p[1]) // a downward crossing
if (isLeft(coord[i], coord[i+1], p) < 0) // p right of edge
--winding; // have a valid down intersect
}
}
return winding;
}
function getCountry(p, data) {
// p: point represented by array with the two coordinates
var country;
return data.feat.some(function (obj) {
country = obj;
var polygons = obj.geometry.coordinates;
if (obj.geometry.type !== 'MultiPolygon') polygons = [polygons];
return polygons.some(function (polygon) {
return inPoly(p, polygon[0]);
});
}) ? country : null;
}
// I/O for this interactive snippet
function drawPolygon(ctx, coord, fillColor) {
ctx.fillStyle = fillColor;
ctx.beginPath();
coord.forEach(function (point, i) {
if (i==0) {
ctx.moveTo(point[0], point[1]);
} else {
ctx.lineTo(point[0], point[1]);
}
});
ctx.fill();
ctx.stroke();
// ctx.closePath();
}
function drawCountry(ctx, selectedCountry, country) {
var polygons = country.geometry.coordinates;
var color = selectedCountry == country ? 'yellow' : 'grey';
if (country.geometry.type !== 'MultiPolygon') polygons = [polygons];
polygons.forEach(function (polygon) {
drawPolygon(ctx, polygon[0], color);
});
}
function drawWorld(ctx, data, selectedCountry) {
data.feat.forEach(drawCountry.bind(null, ctx, selectedCountry));
}
// Define transformation so countries will be mapped to canvas area
var scale = [3, -3];
var move = [-20, 130];
var canvas = document.querySelector('canvas');
var ctx = canvas.getContext("2d");
ctx.translate(...move);
ctx.scale(...scale);
ctx.lineWidth = 1/scale[0];
// Sample data
var data = {"feat":[{"type":"Feature","id":"AFG","properties":{"name":"Afghanistan"},"geometry":{"type":"Polygon","coordinates":[[[61.210817,35.650072],[62.230651,35.270664],[62.984662,35.404041],[63.193538,35.857166],[63.982896,36.007957],[64.546479,36.312073],[64.746105,37.111818],[65.588948,37.305217],[65.745631,37.661164],[66.217385,37.39379],[66.518607,37.362784],[67.075782,37.356144],[67.83,37.144994],[68.135562,37.023115],[68.859446,37.344336],[69.196273,37.151144],[69.518785,37.608997],[70.116578,37.588223],[70.270574,37.735165],[70.376304,38.138396],[70.806821,38.486282],[71.348131,38.258905],[71.239404,37.953265],[71.541918,37.905774],[71.448693,37.065645],[71.844638,36.738171],[72.193041,36.948288],[72.63689,37.047558],[73.260056,37.495257],[73.948696,37.421566],[74.980002,37.41999],[75.158028,37.133031],[74.575893,37.020841],[74.067552,36.836176],[72.920025,36.720007],[71.846292,36.509942],[71.262348,36.074388],[71.498768,35.650563],[71.613076,35.153203],[71.115019,34.733126],[71.156773,34.348911],[70.881803,33.988856],[69.930543,34.02012],[70.323594,33.358533],[69.687147,33.105499],[69.262522,32.501944],[69.317764,31.901412],[68.926677,31.620189],[68.556932,31.71331],[67.792689,31.58293],[67.683394,31.303154],[66.938891,31.304911],[66.381458,30.738899],[66.346473,29.887943],[65.046862,29.472181],[64.350419,29.560031],[64.148002,29.340819],[63.550261,29.468331],[62.549857,29.318572],[60.874248,29.829239],[61.781222,30.73585],[61.699314,31.379506],[60.941945,31.548075],[60.863655,32.18292],[60.536078,32.981269],[60.9637,33.528832],[60.52843,33.676446],[60.803193,34.404102],[61.210817,35.650072]]]}},{"type":"Feature","id":"AGO","properties":{"name":"Angola"},"geometry":{"type":"MultiPolygon","coordinates":[[[[16.326528,-5.87747],[16.57318,-6.622645],[16.860191,-7.222298],[17.089996,-7.545689],[17.47297,-8.068551],[18.134222,-7.987678],[18.464176,-7.847014],[19.016752,-7.988246],[19.166613,-7.738184],[19.417502,-7.155429],[20.037723,-7.116361],[20.091622,-6.94309],[20.601823,-6.939318],[20.514748,-7.299606],[21.728111,-7.290872],[21.746456,-7.920085],[21.949131,-8.305901],[21.801801,-8.908707],[21.875182,-9.523708],[22.208753,-9.894796],[22.155268,-11.084801],[22.402798,-10.993075],[22.837345,-11.017622],[23.456791,-10.867863],[23.912215,-10.926826],[24.017894,-11.237298],[23.904154,-11.722282],[24.079905,-12.191297],[23.930922,-12.565848],[24.016137,-12.911046],[21.933886,-12.898437],[21.887843,-16.08031],[22.562478,-16.898451],[23.215048,-17.523116],[21.377176,-17.930636],[18.956187,-17.789095],[18.263309,-17.309951],[14.209707,-17.353101],[14.058501,-17.423381],[13.462362,-16.971212],[12.814081,-16.941343],[12.215461,-17.111668],[11.734199,-17.301889],[11.640096,-16.673142],[11.778537,-15.793816],[12.123581,-14.878316],[12.175619,-14.449144],[12.500095,-13.5477],[12.738479,-13.137906],[13.312914,-12.48363],[13.633721,-12.038645],[13.738728,-11.297863],[13.686379,-10.731076],[13.387328,-10.373578],[13.120988,-9.766897],[12.87537,-9.166934],[12.929061,-8.959091],[13.236433,-8.562629],[12.93304,-7.596539],[12.728298,-6.927122],[12.227347,-6.294448],[12.322432,-6.100092],[12.735171,-5.965682],[13.024869,-5.984389],[13.375597,-5.864241],[16.326528,-5.87747]]],[[[12.436688,-5.684304],[12.182337,-5.789931],[11.914963,-5.037987],[12.318608,-4.60623],[12.62076,-4.438023],[12.995517,-4.781103],[12.631612,-4.991271],[12.468004,-5.248362],[12.436688,-5.684304]]]]}},{"type":"Feature","id":"ALB","properties":{"name":"Albania"},"geometry":{"type":"Polygon","coordinates":[[[20.590247,41.855404],[20.463175,41.515089],[20.605182,41.086226],[21.02004,40.842727],[20.99999,40.580004],[20.674997,40.435],[20.615,40.110007],[20.150016,39.624998],[19.98,39.694993],[19.960002,39.915006],[19.406082,40.250773],[19.319059,40.72723],[19.40355,41.409566],[19.540027,41.719986],[19.371769,41.877548],[19.304486,42.195745],[19.738051,42.688247],[19.801613,42.500093],[20.0707,42.58863],[20.283755,42.32026],[20.52295,42.21787],[20.590247,41.855404]]]}}]};
// Show map on canvas
window.onload = drawWorld.bind(null, ctx, data, null);
// Handle mouse move to mention the matching country
canvas.onmousemove = function (e) {
// Get mouse coordinates relative to canvas
var x = e.pageX - this.offsetLeft;
var y = e.pageY - this.offsetTop;
// Perform the reverse of the canvas transformation
x = (x - move[0]) / scale[0];
y = (y - move[1]) / scale[1];
// Get country that contains this point
var country = getCountry([x, y], data);
var countryName = country ? country.properties.name : 'no match';
// Output the result
document.getElementById('country').textContent = countryName;
// Highight country
drawWorld(ctx, data, country)
};canvas { border:1px solid; float: left }<canvas width="250", height="200"></canvas>
<div id="country">Hover mouse...</div>有关性能的说明
当数据集中有大量多边形列表时，检查每个多边形的每条边以确定点的适合位置确实是浪费时间。
如果您对数据进行预处理并向每个多边形添加框信息，这将是一个重大改进:完全包围多边形的正方形 ([minx,miny]-[maxx,maxy]) 。当你需要匹配一个点时，你会首先匹配这个盒子，如果它在外面，你可以跳过那个多边形，节省时间。通常只有几个盒子包含您的点，因此您只需要针对这几个多边形进行测试。
要获取国家/地区名称:
像上面的代码片段中那样调用 getCountry 函数，其中传递用户定义的 x 和 y (即经度、 latitude) 作为数组，data 对象作为第二个参数:
var country = getCountry([x, y], data);
var countryName = country ? country.properties.name : 'no match';
关于javascript - 从数组中查找国家坐标，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/39315190/