Mapbox GL JS: Export map to PNG or PDF?

2019-04-04 17:11发布

站内问答 / 前沿技术
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I'm using Mapbox GL JS version 0.32. Is there a way to export the map to a high-res PNG or PDF?

Obviously, I can just screenshot, but it would be nice if there was a more formal way.

I found this repo, but it looks old and isn't clear how it works.

I tried using the preserveDrawingBuffer option:

var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/light-v9',
    minZoom: 4,
    maxZoom: 14,
    center: [-2.0, 53.3],
    preserveDrawingBuffer: true
});
console.log(map.getCanvas().toDataURL());

This outputs a long data URL in the console, but copying and pasting it into a base64 converter just seems to produce an empty image.

UPDATE: This is my new code, in full:

mapboxgl.accessToken = 'pk.eyXXX';
var map = new mapboxgl.Map({
    container: 'map',
    style: 'mapbox://styles/mapbox/light-v9',
    minZoom: 4,
    maxZoom: 14,
    center: [-2.0, 53.3],
    preserveDrawingBuffer: true
});
var dpi = 300;
Object.defineProperty(window, 'devicePixelRatio', {
    get: function() {return dpi / 96}
});

map.on('load', function () {
    var content = map.getCanvas().toDataURL();
    console.log(content)
});

The output to the console is this: http://pastebin.com/raw/KhyJkJWJ

2条回答
Anthone
2楼-- · 2019-04-04 17:40

I created a simple working example for anybody stumbling upon this thread:

(Thanks @Vic for pointing out the preserveDrawingBuffer-option in Mapbox GL JS)

<!DOCTYPE html>
<html>

<head>
    <meta charset='utf-8' />
    <title>Display a map</title>
    <meta name='viewport' content='initial-scale=1,maximum-scale=1,user-scalable=no' />
    <script src='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.js'></script>
    <link href='https://api.tiles.mapbox.com/mapbox-gl-js/v0.44.1/mapbox-gl.css' rel='stylesheet' />
    <script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
    <style>
    #map {
        margin: auto;
        width: 400px;
        height: 400px;
    }
    </style>
</head>

<body>
    <div id='map'></div>
    <a id="downloadLink" href="" download="map.png">Download ↓</a>
    <div id="image"></div>
    <script>
    mapboxgl.accessToken = 'your-token-here';
    var map = new mapboxgl.Map({
        container: 'map',
        style: 'mapbox://styles/mapbox/streets-v9',
        center: [-74.50, 40],
        zoom: 9,
        preserveDrawingBuffer: true
    });

    $('#downloadLink').click(function() {
        var img = map.getCanvas().toDataURL('image/png')
        this.href = img
    })
    </script>
</body>

</html>
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老娘就宠你
3楼-- · 2019-04-04 17:56

There are two main questions:

1. How do I get the map canvas as an image?

Actually, you are doing the right thing, but just too early. Give that map some time to load and fetch the image data when the load event is triggered:

map.on('load', () => console.log(map.getCanvas().toDataURL()));

2. How do I get that image in high-res?

By changing window.devicePixelRatio according to your destination dpi, you can trick your browser into generating high-res output. I found that solution in an implementation created by Matthew Petroff, see his code on https://github.com/mpetroff/print-maps. This is the trick he's using for generating high-res output:

Object.defineProperty(window, 'devicePixelRatio', {
    get: function() {return dpi / 96}
});

Source

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