ol-map-screenshot

ol-map-screenshot is a simple and easy-to-use library to provide the OpenLayers map screenshot. ol-map-screenshot is inspired by Map Export and Export PDF examples by OpenLayers.

Currently, ol-map-screenshot requires OpenLayers version 6.x.

Features

• Promise-based API (async/await).
• Customizable screenshot options using JSON format.
• JPEG and PNG image format support.
• Map scale bar rendering in the screenshot.
• Screenshot metadata provided in the response.

Basic usage

Install the ol-map-screenshot package using npm:

npm i ol-map-screenshot

To use the library just import it into the application:

import olMapScreenshot from 'ol-map-screenshot';

const response = await olMapScreenshot.getScreenshot(map);
//response is JSON object. response.img will store the image in base 64
...

By default, the screenshot is the map size.

Option usage

Parameters can be specified to customize map screenshot:

import olMapScreenshot from 'ol-map-screenshot';

const response = await olMapScreenshot.getScreenshot(map, {
    dim: [190, 160], 
    scaleBarLength: 100
});

Screenshot parameters JSON object

| name | value | Required | Description | | --- | --- | --- | --- | | dim | array | N | Desired image size in mm [width, height]. | | showDisplayScale | boolean | N | Map scale bar is displayed. Default is true | | scaleBarLength | number | N | Map scale bar length. Default is 140 px | | format | 'png' | N | Export format of the image. Default is 'jpeg' | | resolution | number | N | Screen resolution. Default is 150 dpi |

Screenshot response JSON object

| name | value | Description | | --- | --- | --- | | img | data:image/format;base64 | The base 64 image | | w | number | Given image width in mm | | h | number | Given image height in mm | | wPixel | number | Image width value in pixels | | hPixel | number | Image height value in pixels | | scaleBarValue | number | Map scale bar value | | scaleLineValue | number | Map scale line value |

CORS

For security reasons, a browser can mark a canvas as tainted when you load images from another domain. In that case the browser blocks canvas exporting. To avoid this block, the tileLoadFunction property is set when creating the tile layer.

getWMSLayer(layer) {
        return new TileLayer({
            title: layer.title,
            source: new TileWMS({
                url: layer.url,
                params: {
                    LAYERS: layer.name,
                    SRS: 'EPSG:3857',
                    FORMAT: 'image/png'
                },
                tileLoadFunction: proxyTileLoader.load
            }),
            visible: true
        });
    }

The ProxyTileLoader.js file is defined below:

const proxy = "...?url="; //set proxy url

module.exports = {    
    load: (tile, src) => {
        const xhr = new XMLHttpRequest();
        xhr.open("GET", proxy + encodeURIComponent(src).replace(/'/g, "%27").replace(/"/g, "%22"));
        xhr.responseType = "arraybuffer";

        xhr.onload = () => {
            const arrayBufferView = new Uint8Array(this.response);
            const blob = new Blob([arrayBufferView], { type: 'image/png' });
            const urlCreator = window.URL || window.webkitURL;
            const imageUrl = urlCreator.createObjectURL(blob);
            tile.getImage().src = imageUrl;
        };
        xhr.onerror = () => {
            console.log("ERROR loading tiles from proxy.");
        };

        xhr.send();
    }
};

Demo

Live Demo | Download demo project

import 'ol/ol.css';
import Map from 'ol/Map';
import View from 'ol/View';
import TileLayer from 'ol/layer/Tile';
import OSM from 'ol/source/OSM';
import olMapScreenshot from 'ol-map-screenshot';
import '@fortawesome/fontawesome-free/css/all.css';
import 'bootstrap/dist/css/bootstrap.min.css';
import 'bootstrap/dist/js/bootstrap.min.js';
import jsPDF from 'jspdf';

const map = new Map({
    layers: [
        new TileLayer({
            source: new OSM()
        })
    ],
    target: 'map',
    view: new View({
        center: [-531626.1241455, 4563250.0861921],
        zoom: 14
    })
});

const mapScreenshotParam = {
    dim: [190, 160]
};

document.getElementById('export-jpeg-button').onclick = async() => {
    doDonwload('map-screenshot.jpg');
};

document.getElementById('export-png-button').onclick = async() => {
    mapScreenshotParam.format = "png";
    doDonwload('map-screenshot.png');
};

document.getElementById('export-pdf-button').onclick = async() => {
    mapScreenshotParam.format = "jpeg";
    const response = await doScreenshot();
    createPDFDocument(response);
};

function createPDFDocument(data) {
    const pdf = new jsPDF('p', 'mm', 'a4');
    pdf.setFont("times");
    pdf.setFontSize(16);
    pdf.setFontStyle("bold");
    const title = "ol-map-screenshop example!";
    const pageWidth = pdf.internal.pageSize.getWidth();
    pdf.text((pageWidth / 2) - (title.length), 20, title);
    pdf.text(pageWidth, 20, title);
    pdf.setFontSize(10);
    pdf.setFontStyle("italic");
    pdf.text(10, 28, "Location: Córdoba, Andalucia, España");
    pdf.addImage(data.img, 'JPEG', 10, 30, data.w, data.h);
    pdf.save('map-screenshot.pdf');
}

async function doDonwload(fileName) {
    const response = await doScreenshot();
    const element = document.createElement('a');
    element.setAttribute('href', response.img);
    element.setAttribute('download', fileName);
    element.style.display = 'none';
    document.body.appendChild(element);
    element.click();
    document.body.removeChild(element);
}

async function doScreenshot() {
    try {
        return await olMapScreenshot.getScreenshot(map, mapScreenshotParam);
    } catch (ex) {
        showloader(false);
        alert(ex.message);
    }
}

Contributing

To load the test locally, you can start a web server with npm start and go to localhost: 9000.

MIT License

Copyright (c) 2020 José María Martínez Luna

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.