I'm in the process of adding a some drawing tools to a map using OpenLayers v5. Once such task requires a custom drawing that is not covered in the docs or out of the box: concentric circles.
I don't really know where to start so I have two questions.
Can I somehow create a single geometry and use the geometryFunction as demonstrated in the examples, or do I need to create multiple features, one for each circle?
And What exactly does a Geometry need when being created as a standalone in order to work with OpenLayers? A collection of X,Y coordinates?
In an attempt to figure this out on my own, using the drawing example from the docs, I tried to grab the coords from the object, and then subsequently recreate it, and add it to the the source manually like below;
const feature = new Feature({
geometry: new Circle(
[
/**
* These are the nubmers that come out of a native Circle drawing
* when console.log'ing the feature.getGeomety.getFlatCoordinates().
* No idea if this is how I'd get or set those values.
*/
[-10448062.740758311, 4941309.912009362],
[ -9953141.960354999, 4941309.912009362],
]
)
});
source.addFeature(feature);
This does not error, but it fails to show the circle.
When the interaction type is Circle the coordinates will contain two pairs of [x,y] the circle center and the current point. That's enough to calculate radius and rotation. Geometry must be a single simple geometry, so concentric circles would need to be converted to a multipolygon.
// OpenLayers default drawing style doesn't include stroke for MultiPolygon
var white = [255, 255, 255, 1];
var blue = [0, 153, 255, 1];
var width = 3;
styles = [
new ol.style.Style({
fill: new ol.style.Fill({
color: [255, 255, 255, 0.5]
})
}),
new ol.style.Style({
stroke: new ol.style.Stroke({
color: white,
width: width + 2
})
}),
new ol.style.Style({
stroke: new ol.style.Stroke({
color: blue,
width: width
})
}),
new ol.style.Style({
image: new ol.style.Circle({
radius: width * 2,
fill: new ol.style.Fill({
color: blue
}),
stroke: new ol.style.Stroke({
color: white,
width: width / 2
})
}),
zIndex: Infinity
})
];
var raster = new ol.layer.Tile({
source: new ol.source.OSM()
});
var source = new ol.source.Vector({wrapX: false});
var vector = new ol.layer.Vector({
source: source,
});
var map = new ol.Map({
layers: [raster, vector],
target: 'map',
view: new ol.View({
center: [-11000000, 4600000],
zoom: 4
})
});
var typeSelect = document.getElementById('type');
var draw; // global so we can remove it later
function addInteraction() {
var value = typeSelect.value;
if (value !== 'None') {
var geometryFunction;
if (value === 'Square') {
value = 'Circle';
geometryFunction = ol.interaction.Draw.createRegularPolygon(4);
} else if (value === 'Box') {
value = 'Circle';
geometryFunction = ol.interaction.Draw.createBox();
} else if (value === 'Star') {
value = 'Circle';
geometryFunction = function(coordinates, geometry) {
var center = coordinates[0];
var last = coordinates[1];
var dx = center[0] - last[0];
var dy = center[1] - last[1];
var radius = Math.sqrt(dx * dx + dy * dy);
var rotation = Math.atan2(dy, dx);
var newCoordinates = [];
var numPoints = 12;
for (var i = 0; i < numPoints; ++i) {
var angle = rotation + i * 2 * Math.PI / numPoints;
var fraction = i % 2 === 0 ? 1 : 0.5;
var offsetX = radius * fraction * Math.cos(angle);
var offsetY = radius * fraction * Math.sin(angle);
newCoordinates.push([center[0] + offsetX, center[1] + offsetY]);
}
newCoordinates.push(newCoordinates[0].slice());
if (!geometry) {
geometry = new ol.geom.Polygon([newCoordinates]);
} else {
geometry.setCoordinates([newCoordinates]);
}
return geometry;
};
} else if (value === 'Concentric') {
value = 'Circle';
geometryFunction = function(coordinates, geometry) {
var center = coordinates[0];
var last = coordinates[1];
var dx = center[0] - last[0];
var dy = center[1] - last[1];
var radius = Math.sqrt(dx * dx + dy * dy);
var rotation = Math.atan2(dy, dx);
var newCoordinates = [];
var numCircles = 3;
for (var i = numCircles; i > 0; --i) {
var circle = new ol.geom.Circle(center, radius * i/numCircles);
newCoordinates.push(ol.geom.Polygon.fromCircle(circle, 64, rotation).getCoordinates());
}
if (!geometry) {
geometry = new ol.geom.MultiPolygon(newCoordinates);
} else {
geometry.setCoordinates(newCoordinates);
}
return geometry;
};
}
draw = new ol.interaction.Draw({
source: source,
type: value,
geometryFunction: geometryFunction,
style: styles
});
draw.on('drawend', function(evt){
if (evt.feature.getGeometry().getType() == 'MultiPolygon') {
var polygons = evt.feature.getGeometry().getPolygons();
for (var i = 0; i < polygons.length; ++i) {
center = ol.extent.getCenter(polygons[i].getExtent());
radius = ol.extent.getWidth(polygons[i].getExtent())/2;
if (i == 0) {
evt.feature.setGeometry(new ol.geom.Circle(center, radius));
} else {
source.addFeature(new ol.Feature(new ol.geom.Circle(center, radius)));
}
}
}
});
var modify = new ol.interaction.Modify({source: source});
map.addInteraction(modify);
map.addInteraction(draw);
}
}
/**
* Handle change event.
*/
typeSelect.onchange = function() {
map.removeInteraction(draw);
addInteraction();
};
addInteraction();html, body {
margin: 0;
padding: 0;
width: 100%;
height: 100%;
}
.map {
width: 100%;
height: 80%;
}<link href="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/css/ol.css" rel="stylesheet" />
<script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script>
<div id="map" class="map"></div>
<form class="form-inline">
<label>Shape type </label>
<select id="type">
<option value="Circle">Circle</option>
<option value="Square">Square</option>
<option value="Box">Box</option>
<option value="Star">Star</option>
<option value="Concentric">Concentric</option>
<option value="None">None</option>
</select>
</form>