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Client-side projection
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Description
This sample shows how to project features to the spatialReference of the map on the client side.The all-week-earthquakes geojson is loaded from the USGS site. A point with WGS84 spatial reference is created from each geoJSON feature representing earthquake location. Then each point is projected from WGS84 to Winkel III spatial reference. The final geometries are added to the map as graphics.
Code
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no">
<title>Client-side projection</title>
<link rel="stylesheet" href="https://js.arcgis.com/3.46/esri/themes/calcite/dijit/calcite.css">
<link rel="stylesheet" href="https://js.arcgis.com/3.46/esri/css/esri.css">
<style>
html,
body,
#mapDiv {
padding: 0;
margin: 0;
height: 100%;
width: 100%;
}
#coordinateString {
position: absolute;
bottom: 10px;
left: 10px;
z-index: 99999;
background: white;
padding: 5px;
font: "Helvetica Neue";
}
</style>
<script src="https://js.arcgis.com/3.46/"></script>
<script>
require([
"esri/map",
"esri/request",
"esri/config",
"esri/geometry/Point",
"esri/SpatialReference",
"esri/geometry/projection",
"esri/geometry/coordinateFormatter",
"esri/symbols/SimpleLineSymbol",
"esri/symbols/SimpleMarkerSymbol",
"esri/Color",
"esri/graphic",
"esri/layers/GraphicsLayer",
"esri/basemaps",
"dojo/domReady!"
], function (Map, esriRequest, esriConfig,
Point, SpatialReference, projection, coordinateFormatter,
SimpleLineSymbol, SimpleMarkerSymbol,
Color, Graphic, GraphicsLayer, esriBasemaps) {
// Use CORS to get earthquakes geojson
esriConfig.defaults.io.corsEnabledServers.push("earthquake.usgs.gov"); // supports CORS
// check if the client side projection engine is supported in the browser.
// The browser must support WebAssembly.
if (!projection.isSupported()) {
alert("client-side projection is not supported");
return;
}
// load the projection module
const projectionPromise = projection.load();
// request all earthquakes for last week as geojson
const dataRequestPromise = esriRequest({
url: "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.geojson",
handleAs: 'json'
});
// load the coordinate formatter module
coordinateFormatter.load();
// coordinateFormatter spatial reference
const geoSpatialReference = new SpatialReference({
wkid: 4326
});
// add a dark gray basemap in winkel III projection
esriBasemaps.winkel = {
baseMapLayers: [{
url: "https://arcgis1.storymaps.esri.com/arcgis/rest/services/basemaps/Esri_WinkelTripel_dark_gray/MapServer"
}],
thumbnailUrl: "",
title: "Winkel"
};
const viewSpatialReference = new SpatialReference({
wkid: 54042 // winkel III
});
// simple marker symbol to represent earthquake locations
const earthquakeMarker = new SimpleMarkerSymbol("solid", 8, null, new Color([238, 69, 0, 0.5]))
// center of the map
const point = new Point({
x: 6832.430696818978,
y: -209082.39095501788,
spatialReference: viewSpatialReference
});
// create a map with winkel III basemap
const map = new Map("mapDiv", {
basemap: "winkel",
center: point,
scale: 166418924.8107909
});
map.on("load", function () {
// earthquakes graphicslayer
const graphicsLayer = new GraphicsLayer();
map.addLayer(graphicsLayer);
projectionPromise.then(function () {
// read the geojson data from esriRequest promise
dataRequestPromise.then(function (response) {
// loop through geojson earthquakes and process the data
response.features.map(function (feature, i) {
const inSpatialReference = new SpatialReference({
wkid: 4326
});
// create a point from a geoJSON point and set its spatialReference to WGS84
const point = new Point(feature.geometry.coordinates, inSpatialReference);
// project the point from WGS84 to winkel III projection
const projectedPoint = projection.project(point, viewSpatialReference);
// create new graphic and set its geometry to the projected point
const attributes = {
ObjectID: i
};
const graphic = new Graphic(projectedPoint, earthquakeMarker, attributes);
// add the graphic representing earthquake location to the graphicslayer
graphicsLayer.add(graphic);
});
})
.otherwise(function (error) {
console.log("error happened while projecting", error);
});
});
});
// listen to mouse-move event of the map and print out the location of the mouse
// on the map in decimal degrees using coordinate formatter.
map.on("mouse-move", function (evt) {
// exit if coordinateFormatter or projection modules are not loaded
if (!coordinateFormatter.isLoaded() || !projection.isLoaded()) {
return;
}
// The point's spatial reference should either be WGS84 or a geographic coordinate system
// so project the point from Winkel III to WGS84.
const wgs84Point = projection.project(evt.mapPoint, geoSpatialReference);
// display the point coordinates in decimal degrees
if (wgs84Point) {
document.getElementById("coordinateString").innerHTML = "Decimal Degrees: " +
coordinateFormatter.toLatitudeLongitude(wgs84Point, "dd", 3);
}
});
});
</script>
</head>
<body class="calcite">
<div id="coordinateString"></div>
<div id="mapDiv"></div>
</body>
</html>