A multipart geometry can be densified by adding interpolated points at regular intervals. Generalizing a multipart geometry simplifies it while preserving its general shape. Densifying a multipart geometry adds more vertices at regular intervals.
Use case
The sample shows a polyline representing a ship's location at irregular intervals. The density of vertices along the ship's route is appropriate to represent the path of the ship at the sample map view's initial scale. However, that level of detail may be too great if you wanted to show a polyline of the ship's movement down the whole of the Willamette river. Then, you might consider generalizing the polyline to still faithfully represent the ship's passage on the river without having an overly complicated geometry.
Densifying a multipart geometry can be used to more accurately represent curved lines or to add more regularity to the vertices making up a multipart geometry.
How to use the sample
Use the sliders to control the parameters of the densify and generalize methods. You can deselect the checkboxes for either method to remove its effect from the result polyline.
How it works
To densify and generalize a polyline:
- Use the static method
GeometryEngine.densify(polyline, maxSegmentLength)to densify the polyline. The resulting polyline will add points along the line so that there are no points greater thanmaxSegmentLengthfrom the next point. - Use the static method
GeometryEngine.generalize(polyline, maxDeviation, true)to generalize the polyline. The resulting polyline will reduce vertices from the line to simplify the shape. None of these points can deviate farther from the original line than maxDeviation. The last parameter,removeDegenerateParts, will clean up extraneous parts if the geometry is multi-part (it will have no effect in this sample). - Note that
maxSegmentLengthandmaxDeviationare in the units of geometry's coordinate system. This could be in degrees in some coordinate systems. In this example, a cartesian coordinate system is used at a small enough scale that geodesic distances are not required.
Relevant API
- GeometryEngine
- Multipoint
- Point
- PointCollection
- Polyline
- SimpleLineSymbol
- SpatialReference
Tags
densify, Edit and Manage Data, generalize, simplify
Sample Code
DensifyAndGeneralize.qml
// [WriteFile Name=DensifyAndGeneralize, Category=Geometry]
// [Legal]
// Copyright 2018 Esri.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// [Legal]
import QtQuick
import QtQuick.Controls
import Esri.ArcGISRuntime
Rectangle {
id: rootRectangle
clip: true
width: 800
height: 600
MapView {
id: mapView
anchors.fill: parent
Component.onCompleted: {
// Set the focus on MapView to initially enable keyboard navigation
forceActiveFocus();
}
// Declare a map with the streets night vector basemap
Map {
Basemap {
initStyle: Enums.BasemapStyleArcGISStreetsNight
}
}
// Add a graphics overlay
GraphicsOverlay {
id: graphicsOverlay
// original multipart red graphic
Graphic {
id: originalMultipointGraphic
zIndex: 0
SimpleMarkerSymbol {
color: "red"
size: 7
style: Enums.SimpleMarkerSymbolStyleCircle
}
Component.onCompleted: {
const pointCollection = createPointCollection();
const multipointBuilder = ArcGISRuntimeEnvironment.createObject("MultipointBuilder", { spatialReference: pointCollection.spatialReference });
multipointBuilder.points = pointCollection;
originalMultipointGraphic.geometry = multipointBuilder.geometry;
mapView.setViewpointGeometryAndPadding(originalMultipointGraphic.geometry, 100);
}
}
// original red dotted line graphic
Graphic {
id: originalLineGraphic
zIndex: 1
SimpleLineSymbol {
color: "red"
style: Enums.SimpleLineSymbolStyleDot
width: 3
}
Component.onCompleted: {
const pointCollection = createPointCollection();
const polylineBuilder = ArcGISRuntimeEnvironment.createObject("PolylineBuilder", { spatialReference: pointCollection.spatialReference });
for (let i = 0; i < pointCollection.size; i++) {
polylineBuilder.addPoint(pointCollection.point(i));
}
originalLineGraphic.geometry = polylineBuilder.geometry;
}
}
// resulting (densified and generalized) multipart magenta graphic
Graphic {
id: resultMultipointGraphic
visible: showResultCheckbox.checked
zIndex: 2
SimpleMarkerSymbol {
color: "magenta"
size: 7
style: Enums.SimpleMarkerSymbolStyleCircle
}
}
// resulting (densified and generalized) multipart magenta graphic
Graphic {
id: resultPolylineGraphic
visible: showResultCheckbox.checked
zIndex: 3
SimpleLineSymbol {
color: "magenta"
width: 3
style: Enums.SimpleLineSymbolStyleSolid
}
}
}
}
function updateGeometry() {
// Get the initial Geometry
let polyline = originalLineGraphic.geometry;
if (!polyline)
return;
// Generalize the polyline
if (generalizeCheckbox.checked)
polyline = GeometryEngine.generalize(polyline, maxDeviationSlider.value, true);
// Densify the polyline
if (densifyCheckbox.checked)
polyline = GeometryEngine.densify(polyline, maxSegmentLengthSlider.value);
// Update the line graphic
resultPolylineGraphic.geometry = polyline;
// Update the multipoint graphic
const multipointBuilder = ArcGISRuntimeEnvironment.createObject("MultipointBuilder", { spatialReference: polyline.spatialReference });
const pointCollection = ArcGISRuntimeEnvironment.createObject("PointCollection", { spatialReference: polyline.spatialReference });
if (polyline.parts.size < 1)
return;
const polylinePoints = polyline.parts.part(0).points();
for (let i = 0; i < polylinePoints.size; i++) {
pointCollection.addPoint(polylinePoints.point(i));
}
multipointBuilder.points = pointCollection;
resultMultipointGraphic.geometry = multipointBuilder.geometry;
}
function createPointCollection() {
const sr = ArcGISRuntimeEnvironment.createObject("SpatialReference", {wkid: 32126});
const pointCollection = ArcGISRuntimeEnvironment.createObject("PointCollection", { spatialReference: sr });
pointCollection.addPointXYZ(2330611.130549, 202360.002957, 0.000000);
pointCollection.addPointXYZ(2330583.834672, 202525.984012, 0.000000);
pointCollection.addPointXYZ(2330574.164902, 202691.488009, 0.000000);
pointCollection.addPointXYZ(2330689.292623, 203170.045888, 0.000000);
pointCollection.addPointXYZ(2330696.773344, 203317.495798, 0.000000);
pointCollection.addPointXYZ(2330691.419723, 203380.917080, 0.000000);
pointCollection.addPointXYZ(2330435.065296, 203816.662457, 0.000000);
pointCollection.addPointXYZ(2330369.500800, 204329.861789, 0.000000);
pointCollection.addPointXYZ(2330400.929891, 204712.129673, 0.000000);
pointCollection.addPointXYZ(2330484.300447, 204927.797132, 0.000000);
pointCollection.addPointXYZ(2330514.469919, 205000.792463, 0.000000);
pointCollection.addPointXYZ(2330638.099138, 205271.601116, 0.000000);
pointCollection.addPointXYZ(2330725.315888, 205631.231308, 0.000000);
pointCollection.addPointXYZ(2330755.640702, 206433.354860, 0.000000);
pointCollection.addPointXYZ(2330680.644719, 206660.240923, 0.000000);
pointCollection.addPointXYZ(2330386.957926, 207340.947204, 0.000000);
pointCollection.addPointXYZ(2330485.861737, 207742.298501, 0.000000);
return pointCollection;
}
Rectangle {
anchors {
fill: controlColumn
margins: -5
}
color: "#f9f9f9"
radius: 5
}
Column {
id: controlColumn
anchors {
left: parent.left
top: parent.top
margins: 10
}
spacing: 5
CheckBox {
id: densifyCheckbox
text: "Densify"
checked: true
}
Text {
text: "Max segment length"
enabled: densifyCheckbox.checked
}
Slider {
id: maxSegmentLengthSlider
from: 100
to: 500
width: 175
value: 100
onValueChanged: updateGeometry();
}
CheckBox {
id: generalizeCheckbox
text: "Generalize"
checked: true
}
Text {
text: "Max deviation"
enabled: generalizeCheckbox.checked
}
Slider {
id: maxDeviationSlider
from: 1
to: 250
width: 175
onValueChanged: updateGeometry();
}
CheckBox {
id: showResultCheckbox
text: "Show Result"
checked: true
}
}
}