Mapbox GL JS で矢尻形マーカー（mapboxgl.Marker 利用）

こんにちは。
Mapbox GL JS で mapboxgl.Marker を使い矢尻形（矢印）マーカーを描きました。svg で形を定義し、色、サイズ、方向を変化させました。矢尻形の先端をマーカー位置として定義しています。

<img width="280" alt="apboxgl.Marker.jpg" src="https://qiita-image-store.s3.amazonaws.com/0/54617/c86bc9e2-fc97-8a9b-b9ad-a540bc609800.jpeg">

```mapboxgl.marker_arrowhead.html
<!DOCTYPE html>
<html>
<head>
    <meta charset='utf-8' />
    <title></title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v1.6.0/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v1.6.0/mapbox-gl.css' rel='stylesheet' />
    <style>
        body { margin:0; padding:0; }
        #map { position:absolute; top:0; bottom:0; width:100%; }
    </style>
</head>
<body>
<style>
.marker {
    display: block;
    border: none;
    cursor: pointer;
    padding: 0;
}
</style>
<div id='map'></div>
<script>
//mapboxgl.accessToken = '<your access token here>';
const map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/light-v9',
    center: [-65.017, -16.457],
    zoom: 5
});
map.addControl(new mapboxgl.NavigationControl());

const markers = {
    "type": "FeatureCollection",
    "features": [
        {
            "type": "Feature",
            "properties": {
                "marker-rotation": 0,
                "marker-color": "red",
                "marker-size": 10
            },
            "geometry": {
                "type": "Point",
                "coordinates": [
                    -66.324462890625,
                    -16.024695711685304
                ]
            }
        },
        {
            "type": "Feature",
            "properties": {
                "marker-rotation": 45,
                "marker-color": "orange",
                "marker-size": 14
            },
            "geometry": {
                "type": "Point",
                "coordinates": [
                    -61.2158203125,
                    -15.97189158092897
                ]
            }
        },
        {
            "type": "Feature",
            "properties": {
                "marker-rotation": 135,
                "marker-color": "green",
                "marker-size": 20
            },
            "geometry": {
                "type": "Point",
                "coordinates": [
                    -63.29223632812499,
                    -18.28151823530889
                ]
            }
        }
    ]
};

markers.features.forEach(marker => {
    const markerSize = marker.properties["marker-size"], markerRotation = marker.properties["marker-rotation"], markerFill = marker.properties["marker-color"];
	const markerData = "<svg width='" + markerSize + "' height='" + markerSize + "' viewBox='0 0 100 100' xmlns='http://www.w3.org/2000/svg' version='1.1'><polygon fill='" + markerFill + "' stroke='black' stroke-width='1' points='20,90 50,10 80,90 50,70' transform='rotate(" + markerRotation + " 50 50)'/></svg>"; // arrowhead

    new mapboxgl.Marker(markerImage(markerData, markerSize), {offset: [-markerSize / 2, -markerSize / 2], rotationAlignment: 'map', pitchAlignment: 'map'})
        .setLngLat(marker.geometry.coordinates)
        .addTo(map);

});

function markerImage(markerData, markerSize) {
    const el = document.createElement('div');
    el.className = 'marker';
    el.style.backgroundImage = "url(data:image/svg+xml;base64," + btoa(markerData) + ')';
    el.style.width = markerSize + 'px';
    el.style.height = markerSize + 'px';
    return el;
}
</script>
</body>
</html>
```