我正在将我的应用程序移至 Mapbox，我遇到的其中一件事是创建多色折线，其中段颜色是根据速度动态设置的。我能做的最接近的事情是创建一组不同颜色的线，并将它们添加到 map 中，但处理时间和帧速率会降低太多，更不用说您可以看到不同的段了。这可以通过 MapKit 或 Google Maps 轻松实现，但据我所知，一条折线在 Mapbox 中只能有一种颜色。
有人问了一个非常相似的问题 Here但那是 3 年前，答案似乎与使用方向 API 有关。
基本功能如下所示，我创建了一个自定义 MGLMulticolorPolyline 类，以便我可以设置颜色
func locationPolyLine(locations : [Location], averageSpeed: Double, topSpeed: Double) -> [MGLMulticolorPolyline] {
var coordinates: [(CLLocation, CLLocation)] = []
var speeds: [Double] = []
let smallerLocationArray = locations.enumerated().filter({ index, _ in
index % 2 != 0
}).map { $0.1 }
for (first, second) in zip(smallerLocationArray, smallerLocationArray.dropFirst()) {
//create an array of coordinates
let start = CLLocation(latitude: first.locLatitude, longitude: first.locLongitude)
let end = CLLocation(latitude: second.locLatitude, longitude: second.locLongitude)
coordinates.append((start, end))
let distance = end.distance(from: start)
guard let firstTimestamp = first.locTimestamp,
let secondTimestamp = second.locTimestamp else {continue}
let time = secondTimestamp.timeIntervalSince(firstTimestamp as Date)
let speed = time > 0 ? distance / time : 0
speeds.append(speed)
}
var segments: [MGLMulticolorPolyline] = []
var index = 0
for ((start, end), speed) in zip(coordinates, speeds) {
let coords = [start.coordinate, end.coordinate]
let segment = MGLMulticolorPolyline(coordinates: coords, count: 2)
if smallerLocationArray[index].lift == true{
segment.color = UIColor.blue
} else{
segment.color = segmentColor(speed: speed,
midSpeed: averageSpeed,
slowestSpeed: 0.0,
fastestSpeed: topSpeed)
}
segments.append(segment)
index += 1
}
return segments
}
}
它像这样被添加到 map 中
let multiColoredPolyline = MapboxHelper().locationPolyLine(locations: locationsArray, averageSpeed: avgSpeed, topSpeed: maxSpeed)
mapView.addAnnotations(multiColoredPolyline)
最佳答案
回过头来，Mapbox 引入了 the line-gradient property 。
https://docs.mapbox.com/mapbox-gl-js/example/line-gradient/ 给出了一个如何使用它的例子。
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Create a gradient line using an expression</title>
<meta name="viewport" content="initial-scale=1,maximum-scale=1,user-scalable=no">
<link href="https://api.mapbox.com/mapbox-gl-js/v2.3.0/mapbox-gl.css" rel="stylesheet">
<script src="https://api.mapbox.com/mapbox-gl-js/v2.3.0/mapbox-gl.js"></script>
<style>
body { margin: 0; padding: 0; }
#map { position: absolute; top: 0; bottom: 0; width: 100%; }
</style>
</head>
<body>
<div id="map"></div>
<script>
// TO MAKE THE MAP APPEAR YOU MUST
// ADD YOUR ACCESS TOKEN FROM
// https://account.mapbox.com
mapboxgl.accessToken = '<your access token here>';
var map = (window.map = new mapboxgl.Map({
container: 'map',
style: 'mapbox://styles/mapbox/light-v10',
center: [-77.035, 38.875],
zoom: 12
}));
var geojson = {
'type': 'FeatureCollection',
'features': [
{
'type': 'Feature',
'properties': {},
'geometry': {
'coordinates': [
[-77.044211, 38.852924],
[-77.045659, 38.860158],
[-77.044232, 38.862326],
[-77.040879, 38.865454],
[-77.039936, 38.867698],
[-77.040338, 38.86943],
[-77.04264, 38.872528],
[-77.03696, 38.878424],
[-77.032309, 38.87937],
[-77.030056, 38.880945],
[-77.027645, 38.881779],
[-77.026946, 38.882645],
[-77.026942, 38.885502],
[-77.028054, 38.887449],
[-77.02806, 38.892088],
[-77.03364, 38.892108],
[-77.033643, 38.899926]
],
'type': 'LineString'
}
}
]
};
map.on('load', function () {
// 'line-gradient' can only be used with GeoJSON sources
// and the source must have the 'lineMetrics' option set to true
map.addSource('line', {
type: 'geojson',
lineMetrics: true,
data: geojson
});
// the layer must be of type 'line'
map.addLayer({
type: 'line',
source: 'line',
id: 'line',
paint: {
'line-color': 'red',
'line-width': 14,
// 'line-gradient' must be specified using an expression
// with the special 'line-progress' property
'line-gradient': [
'interpolate',
['linear'],
['line-progress'],
0,
'blue',
0.1,
'royalblue',
0.3,
'cyan',
0.5,
'lime',
0.7,
'yellow',
1,
'red'
]
},
layout: {
'line-cap': 'round',
'line-join': 'round'
}
});
});
</script>
</body>
</html>
在代码中有点难看，他们在文档中根本没有解释，但是 https://github.com/mapbox/path-gradients/blob/master/main.js#L22 行是你可以设置任何你想要的颜色的地方，所以不要选择依赖于位置的颜色
ith 元素，您可以根据 ith 元素的速度设置颜色。
关于swift - Mapbox 多色折线，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/58582527/