arcgis学习系列11--绘制不自己交叉的Polygon
概述
本文演示如何阻止用户使用Draw画子线交叉的线。
Draw操作使用视图事件生成一组坐标，可以从中创建不同类型的几何图形。每种几何类型都有一个对应的draw action类。实例化Draw之后，调用 draw.create()方法将返回一个draw Action的引用。
在这一篇文章中，draw.create()方法被调用，并传递polyline作为参数，我们监听PolylineDrawAction的相关事件实现自己的逻辑，即：组织用户绘制自相交叉的线。
// draw polyline button
document.getElementById("line-button").onclick = function() {
view.graphics.removeAll();
// creates and returns an instance of PolyLineDrawAction
const action = draw.create("polyline");
// focus the view to activate keyboard shortcuts for sketching
view.focus();
// listen polylineDrawAction events to give immediate visual feedback
// to users as the line is being drawn on the view.
action.on("vertex-add", updateVertices);
action.on("vertex-remove", updateVertices);
action.on("cursor-update", updateVertices);
action.on("redo", updateVertices);
action.on("undo", updateVertices);
action.on("draw-complete", updateVertices);
};
完整代码
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport"
content="initial-scale=1,maximum-scale=1,user-scalable=no" />
<!--
ArcGIS API for JavaScript, https://js.arcgis.com
For more information about the draw-line sample, read the original sample description at developers.arcgis.com.
https://developers.arcgis.com/javascript/latest/sample-code/draw-line/index.html
-->
<title>Draw polyline - 4.11</title>
<link rel="stylesheet"
href="https://js.arcgis.com/4.11/esri/themes/light/main.css" />
<script src="https://js.arcgis.com/4.11/"></script>
<style>
html,
body,
#viewDiv {
height: 100%;
width: 100%;
margin: 0;
padding: 0;
}
</style>
<script>
require([
"esri/Map",
"esri/views/MapView",
"esri/views/draw/Draw",
"esri/Graphic",
"esri/geometry/geometryEngine"
], function(Map, MapView, Draw, Graphic, geometryEngine) {
const map = new Map({
basemap: "gray"
});
const view = new MapView({
container: "viewDiv",
map: map,
zoom: 16,
center: [18.06, 59.34]
});
// add the button for the draw tool
view.ui.add("line-button", "top-left");
const draw = new Draw({
view: view
});
// draw polyline button
document.getElementById("line-button").onclick = function() {
view.graphics.removeAll();
// creates and returns an instance of PolyLineDrawAction
const action = draw.create("polyline");
// focus the view to activate keyboard shortcuts for sketching
view.focus();
// listen polylineDrawAction events to give immediate visual feedback
// to users as the line is being drawn on the view.
action.on(
[
"vertex-add",
"vertex-remove",
"cursor-update",
"redo",
"undo",
"draw-complete"
],
updateVertices
);
};
// Checks if the last vertex is making the line intersect itself.
function updateVertices(event) {
// create a polyline from returned vertices
if (event.vertices.length > 1) {
const result = createGraphic(event);
// if the last vertex is making the line intersects itself,
// prevent the events from firing
if (result.selfIntersects) {
event.preventDefault();
}
}
}
// create a new graphic presenting the polyline that is being drawn on the view
function createGraphic(event) {
const vertices = event.vertices;
view.graphics.removeAll();
// a graphic representing the polyline that is being drawn
const graphic = new Graphic({
geometry: {
type: "polyline",
paths: vertices,
spatialReference: view.spatialReference
},
symbol: {
type: "simple-line", // autocasts as new SimpleFillSymbol
color: [4, 90, 141],
width: 4,
cap: "round",
join: "round"
}
});
// check if the polyline intersects itself.
const intersectingSegment = getIntersectingSegment(graphic.geometry);
// Add a new graphic for the intersecting segment.
if (intersectingSegment) {
view.graphics.addMany([graphic, intersectingSegment]);
}
// Just add the graphic representing the polyline if no intersection
else {
view.graphics.add(graphic);
}
// return intersectingSegment
return {
selfIntersects: intersectingSegment
};
}
// function that checks if the line intersects itself
function isSelfIntersecting(polyline) {
if (polyline.paths[0].length < 3) {
return false;
}
const line = polyline.clone();
//get the last segment from the polyline that is being drawn
const lastSegment = getLastSegment(polyline);
line.removePoint(0, line.paths[0].length - 1);
// returns true if the line intersects itself, false otherwise
return geometryEngine.crosses(lastSegment, line);
}
// Checks if the line intersects itself. If yes, change the last
// segment's symbol giving a visual feedback to the user.
function getIntersectingSegment(polyline) {
if (isSelfIntersecting(polyline)) {
return new Graphic({
geometry: getLastSegment(polyline),
symbol: {
type: "simple-line", // autocasts as new SimpleLineSymbol
style: "short-dot",
width: 3.5,
color: "yellow"
}
});
}
return null;
}
// Get the last segment of the polyline that is being drawn
function getLastSegment(polyline) {
const line = polyline.clone();
const lastXYPoint = line.removePoint(0, line.paths[0].length - 1);
const existingLineFinalPoint = line.getPoint(
0,
line.paths[0].length - 1
);
return {
type: "polyline",
spatialReference: view.spatialReference,
hasZ: false,
paths: [
[
[existingLineFinalPoint.x, existingLineFinalPoint.y],
[lastXYPoint.x, lastXYPoint.y]
]
]
};
}
});
</script>
</head>
<body>
<div id="viewDiv">
<div id="line-button"
class="esri-widget esri-widget--button esri-interactive"
title="Draw polyline">
<span class="esri-icon-polyline"></span>
</div>
</div>
</body>
</html>