Calculate a viewshed using a geoprocessing service, in this case showing which parts of a landscape are visible from points on mountainous terrain.
Use case
A viewshed is used to highlight what is visible from a given point. A viewshed could be created to show what a hiker might be able to see from a given point at the top of a mountain. Equally, a viewshed could also be created from a point representing the maximum height of a proposed wind turbine to see from what areas the turbine would be visible.
How to use the sample
Click the map to see all areas visible from that point within a 15km radius. Clicking on an elevated area will highlight a larger part of the surrounding landscape. It may take a few seconds for the task to run and send back the results.
How it works
- Create a
GeoprocessingTaskobject with the URL set to a geoprocessing service endpoint. - Create a
FeatureCollectionTableobject and add a newFeatureobject whose geometry is the viewshed's observerPoint. - Make a
GeoprocessingParametersobject passing in the observer point. - Use the geoprocessing task to create a
GeoprocessingJobobject with the parameters. - Start the job and wait for it to complete and return a
GeoprocessingResultobject. - Get the resulting
GeoprocessingFeaturesobject. - Iterate through the viewshed features to use their geometry or display the geometry in a new
Graphicobject.
Relevant API
- FeatureCollectionTable
- GeoprocessingFeatures
- GeoprocessingJob
- GeoprocessingParameters
- GeoprocessingResult
- GeoprocessingTask
Tags
geoprocessing, heat map, heatmap, viewshed
Sample Code
AnalyzeViewshed.qml
// [WriteFile Name=AnalyzeViewshed, Category=Analysis]
// [Legal]
// Copyright 2016 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 QtQuick.Layouts
import Esri.ArcGISRuntime
Rectangle {
id: rootRectangle
clip: true
width: 800
height: 600
property bool viewshedInProgress: false
property GeoprocessingJob viewshedJob: null
property string statusText: ""
// Map view UI presentation at top
MapView {
id: mapView
anchors.fill: parent
Component.onCompleted: {
// Set the focus on MapView to initially enable keyboard navigation
forceActiveFocus();
}
// Create map with topographic basemap and initial viewpoint
Map {
Basemap {
initStyle: Enums.BasemapStyleArcGISTopographic
}
ViewpointCenter {
Point {
x: 6.84905317262762
y: 45.3790902612337
spatialReference: Factory.SpatialReference.createWgs84()
}
targetScale: 100000
}
}
// Create the graphics overlays for the input and output
GraphicsOverlay {
id: inputOverlay
// Set the size and color properties for the simple renderer
SimpleRenderer {
SimpleMarkerSymbol {
color: "red"
style: Enums.SimpleMarkerSymbolStyleCircle
size: 12
}
}
}
GraphicsOverlay {
id: resultsOverlay
// Set the size and color properties for the simple renderer
SimpleRenderer {
SimpleFillSymbol {
color: Qt.rgba(0.88, 0.46, 0.16, 0.4)
}
}
}
// Set up signal handler for the mouse clicked signal
onMouseClicked: mouse => {
// The geoprocessing task is still executing, don't do anything else (i.e. respond to
// more user taps) until the processing is complete.
if (viewshedInProgress)
return;
// Indicate that the geoprocessing is running
viewshedInProgress = true;
// Clear previous user click location and the viewshed geoprocessing task results
inputOverlay.graphics.clear();
resultsOverlay.graphics.clear();
// Create a marker graphic where the user clicked on the map and add it to the existing graphics overlay
const inputGraphic = ArcGISRuntimeEnvironment.createObject("Graphic", {geometry: mouse.mapPoint});
inputOverlay.graphics.append(inputGraphic);
// Execute the geoprocessing task
viewshedTask.calculateViewshed(mouse.mapPoint);
}
}
// Create the GeoprocessingTask
GeoprocessingTask {
id: viewshedTask
url: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Elevation/ESRI_Elevation_World/GPServer/Viewshed"
onErrorChanged: {
viewshedInProgress = false;
if (error)
showErrorDialog(error);
}
// function to caclulate the viewshed
function calculateViewshed(location) {
// Create a new feature collection table based upon point geometries using the current map view spatial reference
const inputFeatures = ArcGISRuntimeEnvironment.createObject("FeatureCollectionTable", {
geometryType: Enums.GeometryTypePoint,
spatialReference: Factory.SpatialReference.createWebMercator()
});
// Create a new feature from the feature collection table. It will not have a coordinate location (x,y) yet
const inputFeature = inputFeatures.createFeature();
// Assign a physical location to the new point feature based upon where the user clicked on the map view
inputFeature.geometry = location;
// connect to addFeature status changed signal
inputFeatures.addFeatureStatusChanged.connect(()=> {
if (inputFeatures.addFeatureStatus === Enums.TaskStatusCompleted) {
// Create the parameters that are passed to the used geoprocessing task
const viewshedParameters = ArcGISRuntimeEnvironment.createObject("GeoprocessingParameters", {
executionType: Enums.GeoprocessingExecutionTypeSynchronousExecute
});
// Request the output features to use the same SpatialReference as the map view
viewshedParameters.outputSpatialReference = Factory.SpatialReference.createWebMercator();
// Add an input location to the geoprocessing parameters
const inputs = {};
inputs["Input_Observation_Point"] = ArcGISRuntimeEnvironment.createObject("GeoprocessingFeatures", { features: inputFeatures });
viewshedParameters.inputs = inputs;
// Create the job that handles the communication between the application and the geoprocessing task
viewshedJob = viewshedTask.createJob(viewshedParameters);
// Create signal handler for the job
viewshedJob.statusChanged.connect(viewshedJobHandler);
// start the job
viewshedJob.start();
}
});
// Add the new feature with (x,y) location to the feature collection table
inputFeatures.addFeature(inputFeature);
}
// function to handle the job as it changes its status
function viewshedJobHandler() {
if (viewshedJob.jobStatus === Enums.JobStatusFailed) {
showErrorDialog(viewshedJob.error);
viewshedInProgress = false;
statusText = "Job failed.";
} else if (viewshedJob.jobStatus === Enums.JobStatusStarted) {
viewshedInProgress = true;
statusText = "Job in progress...";
} else if (viewshedJob.jobStatus === Enums.JobStatusPaused) {
viewshedInProgress = false;
statusText = "Job paused...";
} else if (viewshedJob.jobStatus === Enums.JobStatusSucceeded) {
// handle the results
processResults(viewshedJob.result);
viewshedInProgress = false;
statusText = "Job succeeded.";
}
}
// function to handle the results from the GeoprocessingJob
function processResults(result) {
// Get the results from the outputs as GeoprocessingFeatures
const viewshedResultFeatures = result.outputs["Viewshed_Result"];
// Add all the features from the result feature set as a graphics to the map
const viewshedAreas = viewshedResultFeatures.features.iterator;
while (viewshedAreas.hasNext) {
const feat = viewshedAreas.next();
const graphic = ArcGISRuntimeEnvironment.createObject("Graphic", {
geometry: feat.geometry
});
resultsOverlay.graphics.append(graphic);
}
}
function showErrorDialog(error) {
messageDialog.title = "Error";
messageDialog.text = "Executing geoprocessing failed.";
messageDialog.detailedText = error ? error.message : "Unknown error";
messageDialog.open();
}
}
// Create rectangle to display the status
Rectangle {
anchors {
margins: -10
fill: statusColumn
}
color: "lightgrey"
radius: 5
border.color: "black"
opacity: 0.85
}
Column {
id: statusColumn
anchors {
right: parent.right
top: parent.top
margins: 20
}
Text {
anchors.margins: 5
visible: !viewshedInProgress
text: "Click map to execute viewshed analysis"
font.pixelSize: 12
}
Row {
anchors.margins: 5
visible: viewshedInProgress
spacing: 10
BusyIndicator {
anchors.verticalCenter: parent.verticalCenter
width: 22
height: width
}
Text {
anchors.verticalCenter: parent.verticalCenter
text: statusText
font.pixelSize: 12
}
}
}
// Dialog to display errors
Dialog {
id: messageDialog
modal: true
x: Math.round(parent.width - width) / 2
y: Math.round(parent.height - height) / 2
standardButtons: Dialog.Ok
title: "Error"
property alias text : textLabel.text
property alias detailedText : detailsLabel.text
ColumnLayout {
Text {
id: textLabel
text: "Executing geoprocessing failed."
}
Text {
id: detailsLabel
}
}
}
}