geojson 圈子，支持不支持？

Question

当我查找 GeoJson 的规格时，我发现支持圆圈：

http://geopriv.dreamhosters.com/geojson/geojson-spec.html#circleExample

当我尝试 geojsonlint (http://geojsonlint.com/) 中的代码时，它给了我一个错误。

输入：

{ 
"type": "Circle",
"coordinates": [4.884, 52.353],
"radius": 200
}

给予：

"Circle" is not a valid GeoJSON type. 

我想用d3在地图上显示具有一定影响力的不同名胜古迹。它需要 GeoJson 进行输入，但 GeoJson 确实不支持圆圈吗？

Answer 1

当我查找 GeoJson 的规格时，我发现支持圆圈

他们不是。看来您找到了一些假的或不正确的规格。去 geojson.org 找到 specs，没有关于圆的内容。

Answer 2

正如接受的答案所解释的那样，GeoJson 规范不支持圆圈。

但是，大多数地图实现都会让您创建圆形，但如果这对您不起作用（例如，您需要将其存储在数据库中并查询它），解决方案是创建一个大致近似于的多边形圆（想象一个具有 32 条以上边的多边形）。

我编写了一个模块来执行此操作。你可以这样使用它：

const circleToPolygon = require('circle-to-polygon');

const coordinates = [-27.4575887, -58.99029]; //[lon, lat]
const radius = 100;                           // in meters
const numberOfEdges = 32;                     //optional that defaults to 32

let polygon = circleToPolygon(coordinates, radius, numberOfEdges);

要澄清为什么不支持圆，这与地球的曲率有关。因为地球不是一个完美的球体，如果你在上面画一个圆形，它也不是一个完美的圆形。但是，上述解决方案适用于大多数不需要严格精度的场景。

Answer 3

geojson 没有圆支持， 但你可以使用 LineString 来模拟圆

使用 LineString 几何对象

"geometry": {
        "type": "LineString",
        "coordinates": [
                    [center_X, center_y],
                    [center_X, center_y]
                ]
      }

然后设置动态样式使用半径作为描边权重

function featureStyle(feature){
    return {
      strokeWeight: radius,
    };
  }

它在地图上看起来像一个圆圈。

Answer 4

对于osm静态地图，只需在template.html中添加一段代码即可：

pointToLayer: function (feature, latlng) {
if (feature.markerIconOptions) {
    return L.marker(latlng, {icon: L.icon(feature.markerIconOptions)})
}
if (feature.properties.radius) {
    return new L.Circle(latlng, feature.properties.radius);
}
return L.marker(latlng, {icon: myIcon});
}

示例：http://localhost:3000/dynamic?geojson=%5B%7B%0A%20%20%20%20%22type%22%3A%20%22Feature%22%2C%0A%20%20% 20%20%22属性%22%3A%20%7B%0A%20%20%20%20%20%20%22半径%22%3A%20500%0A%20%20%20%20%7D%2C% 0A%20%20%20%20%22几何%22%3A%20%7B%20%22类型%22%3A%20%22点%22%2C%20%22坐标%22%3A%20%5B16.359459% 2C%2048.203747%5D%20%7D%0A%7D%2C%0A%7B%0A%20%20%20%20%22类型%22%3A%20%22功能%22%2C%0A%20%20% 20%20%22属性%22%3A%20%7B%0A%20%20%20%20%20%20%22半径%22%3A%20500%0A%20%20%20%20%7D%2C% 0A%20%20%20%20%22几何%22%3A%20%7B%20%22类型%22%3A%20%22点%22%2C%20%22坐标%22%3A%20%5B16.359969% 2C%2048.203850%5D%20%7D%0A%7D%5D

Answer 5

A circle... some code I use for making a circle for an OpenStreetMap

-- x is decimal latitude
-- y is decimal longitude
-- r is radius --  .00010 is about 40m in OSM (3 about 50km)

-- Adjust for map latitude distortion further north or south

x = math.log(math.tan((90 + x) * math.pi/360)) / (math.pi/180)

-- For loop to gather all the points of circle here 1 to 360
-- can also use the for loop to make some other interesting shapes

for i = 1, 360 do
    angle = i * math.pi / 180
    ptx = x + r * math.cos( angle )
    pty = y + r * math.sin( angle )

-- readjust latitude for map distortion

    ptx = 180/math.pi * (2 * math.atan(math.exp( ptx * math.pi/180)) - math.pi/2 )

-- Build an array of positions for GeoJSON - formatted lat and long

    data[i] = '[' .. string.format("%.6f",pty) .. ","
    data[i] = data[i] .. string.format("%.6f",ptx) .. ']'

-- End of for loop
end

-- Cycle through the data array with another for loop to build the
   coordinates (put in brackets and commas etc. for the actual
   GeoJSON coordinates string. Add data[1] to the end to close
   the polygon (circle). A circle.

-- If you want a solid circle then use fill and a hex color
-- If you want a LineString just make fill invisible or #ffffff
      Include the stroke-width and stroke-color parameters as well.
-- If latitude is greater than 89.5 or less than -89.5 you may wish
   to cut off the circle by drawing a line at polar regions by using
   those latitudes.
-- I use this simply for several circles and not for hundreds of them.

Cheers!
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