Viewshed (GeoElement)

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Sample viewer app

Analyze the viewshed for an object (GeoElement) in a scene.

screenshot

Use case

A viewshed analysis is a type of visual analysis you can perform on a scene. The viewshed aims to answer the question 'What can I see from a given location?'. The output is an overlay with two different colors - one representing the visible areas (green) and the other representing the obstructed areas (red).

How to use the sample

Tap to set a destination for the vehicle (a GeoElement). The vehicle will 'drive' towards the tapped location. The viewshed analysis will update as the vehicle moves.

How it works

  1. Create and show the scene, with an elevation source and a buildings layer.
  2. Add a model (the GeoElement) to represent the observer (in this case, a tank).
    • Use a SimpleRenderer which has a heading expression set in the GraphicsOverlay. This way you can relate the viewshed's heading to the GeoElement object's heading.
  3. Create a GeoElementViewshed with configuration for the viewshed analysis.
  4. Add the viewshed to an AnalysisOverlay and add the overlay to the scene.
  5. Configure the SceneView CameraController to orbit the vehicle.

Relevant API

  • AnalysisOverlay
  • GeodeticDistanceResult
  • GeoElementViewshed
  • GeometryEngine::distanceGeodetic (used to animate the vehicle)
  • ModelSceneSymbol
  • OrbitGeoElementCameraController

Offline data

Offline sample data will be downloaded by the sample viewer automatically.

Link Local Location
Model Marker Symbol Data <userhome>/ArcGIS/Runtime/Data/3D/bradley_low_3ds/bradle.3ds

About the data

This sample shows a Johannesburg, South Africa Scene from ArcGIS Online. The sample uses a Tank model scene symbol hosted as an item on ArcGIS Online.

Tags

3D, analysis, buildings, model, scene, viewshed, visibility analysis

Sample Code

ViewshedGeoElement.cppViewshedGeoElement.cppViewshedGeoElement.hViewshedGeoElement.qml
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// [WriteFile Name=ViewshedGeoElement, Category=Analysis]
// [Legal]
// Copyright 2017 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]

#ifdef PCH_BUILD
#include "pch.hpp"
#endif // PCH_BUILD

#include "ViewshedGeoElement.h"

#include "ArcGISTiledElevationSource.h"
#include "Scene.h"
#include "SceneQuickView.h"
#include "Camera.h"
#include "Point.h"
#include "Viewpoint.h"
#include "ArcGISSceneLayer.h"
#include "SimpleRenderer.h"
#include "ModelSceneSymbol.h"
#include "GeoElementViewshed.h"
#include "GeometryEngine.h"
#include "OrbitGeoElementCameraController.h"

#include <QTimer>
#include <QString>
#include <QUrl>
#include <QVariant>
#include <QList>
#include <QDir>
#include <QtCore/qglobal.h>

#ifdef Q_OS_IOS
#include <QStandardPaths>
#endif // Q_OS_IOS

using namespace Esri::ArcGISRuntime;

// helper method to get cross platform data path
namespace
{
  QString defaultDataPath()
  {
    QString dataPath;

  #ifdef Q_OS_ANDROID
    dataPath = "/sdcard";
  #elif defined Q_OS_IOS
    dataPath = QStandardPaths::writableLocation(QStandardPaths::DocumentsLocation);
  #else
    dataPath = QDir::homePath();
  #endif

    return dataPath;
  }
} // namespace

ViewshedGeoElement::ViewshedGeoElement(QQuickItem* parent /* = nullptr */):
  QQuickItem(parent)
{
}

void ViewshedGeoElement::init()
{
  // Register classes for QML
  qmlRegisterType<SceneQuickView>("Esri.Samples", 1, 0, "SceneView");
  qmlRegisterType<ViewshedGeoElement>("Esri.Samples", 1, 0, "ViewshedGeoElementSample");
}

void ViewshedGeoElement::componentComplete()
{
  QQuickItem::componentComplete();

  // Create a scene and give it to the SceneView
  m_sceneView = findChild<SceneQuickView*>("sceneView");
  Scene* scene = new Scene(BasemapStyle::ArcGISImageryStandard, this);

  // Create a surface
  Surface* surface = new Surface(this);
  surface->elevationSources()->append(
        new ArcGISTiledElevationSource(
          QUrl("https://scene.arcgis.com/arcgis/rest/services/BREST_DTM_1M/ImageServer"),
          this));
  scene->setBaseSurface(surface);

  // Add a SceneLayer
  ArcGISSceneLayer* sceneLayer = new ArcGISSceneLayer(QUrl("https://tiles.arcgis.com/tiles/P3ePLMYs2RVChkJx/arcgis/rest/services/Buildings_Brest/SceneServer/layers/0"), this);
  scene->operationalLayers()->append(sceneLayer);

  // Add an AnalysisOverlay
  m_analysisOverlay = new AnalysisOverlay(this);
  m_sceneView->analysisOverlays()->append(m_analysisOverlay);

  // Add a GraphicsOverlay
  createGraphicsOverlay();

  // Create a Graphic
  createGraphic();

  // Create the GeoElementViewshed
  const double horizontalAngle = 90.0;
  const double verticalAngle = 25.0;
  const double minDistance = 5.0;
  const double maxDistance = 250.0;
  const double headingOffset = 0.0;
  const double pitchOffset = 0.0;
  m_viewshed = new GeoElementViewshed(m_tank, horizontalAngle,
                                      verticalAngle, minDistance,
                                      maxDistance, headingOffset,
                                      pitchOffset, this);
  m_viewshed->setOffsetY(0.5);
  m_viewshed->setOffsetZ(0.5);
  m_analysisOverlay->analyses()->append(m_viewshed);

  // Add the Scene to the SceneView
  m_sceneView->setArcGISScene(scene);

  // create the camera controller to follow the graphic
  OrbitGeoElementCameraController* followingController = new OrbitGeoElementCameraController(m_tank, 200.0, this);
  followingController->setCameraPitchOffset(45.0);
  m_sceneView->setCameraController(followingController);

  // Create a Timer
  m_timer = new QTimer(this);
  m_timer->setInterval(100);
  connect(m_timer, &QTimer::timeout, this, &ViewshedGeoElement::animate);

  // connect to the mouse clicked signal
  connect(m_sceneView, &SceneQuickView::mouseClicked, this, [this](QMouseEvent& event)
  {
    m_waypoint = m_sceneView->screenToBaseSurface(event.x(), event.y());
    m_timer->start();
  });
}

void ViewshedGeoElement::createGraphicsOverlay()
{
  // Add a GraphicsOverlay
  m_graphicsOverlay = new GraphicsOverlay(this);
  m_sceneView->graphicsOverlays()->append(m_graphicsOverlay);

  // Set the SurfacePlacement
  LayerSceneProperties sceneProperties = m_graphicsOverlay->sceneProperties();
  sceneProperties.setSurfacePlacement(SurfacePlacement::Relative);
  m_graphicsOverlay->setSceneProperties(sceneProperties);

  // Set a Renderer
  SimpleRenderer* simpleRenderer = new SimpleRenderer(this);
  const QString headingExpression = QString("[%1]").arg(m_headingAttr);
  simpleRenderer->setSceneProperties(RendererSceneProperties(headingExpression, "", ""));
  m_graphicsOverlay->setRenderer(simpleRenderer);
}

void ViewshedGeoElement::createGraphic()
{
  // Create the Graphic Point
  const double x = -4.508708007847015;
  const double y = 48.38823243446344;
  const double z = 0;
  const Point tankPoint(x, y, z, SpatialReference(4326));
  const float scale = 10;

  // Create the Graphic Symbol
  ModelSceneSymbol* sceneSymbol = new ModelSceneSymbol(QUrl(defaultDataPath() + "/ArcGIS/Runtime/Data/3D/bradley_low_3ds/bradle.3ds"), scale, this);
  sceneSymbol->setAnchorPosition(SceneSymbolAnchorPosition::Bottom);
  sceneSymbol->setHeading(90.0f);

  // Create the Graphic
  QVariantMap attr;
  attr[m_headingAttr] = 150.0;
  m_tank = new Graphic(tankPoint, attr, sceneSymbol, this);
  m_graphicsOverlay->graphics()->append(m_tank);
}

void ViewshedGeoElement::animate()
{
  if (m_waypoint.isEmpty())
    return;

  // get current location and distance from waypoint
  Point location = m_tank->geometry();
  const GeodeticDistanceResult distance = GeometryEngine::distanceGeodetic(location, m_waypoint,
                                                                           m_linearUnit, m_angularUnit,
                                                                           m_curveType);

  // move toward waypoint based on speed and update orientation
  location = GeometryEngine::moveGeodetic(QList<Point>{location}, 1.0, m_linearUnit,
                                          distance.azimuth1(), m_angularUnit,
                                          m_curveType).at(0);
  m_tank->setGeometry(location);

  // update the heading
  const double heading = m_tank->attributes()->attributeValue(m_headingAttr).toDouble();
  const QString newHeading = QString::number(heading + (distance.azimuth1() - heading) / 10);
  m_tank->attributes()->replaceAttribute(m_headingAttr, newHeading);

  // reached waypoint
  if (distance.distance() <= 5)
  {
    m_waypoint = Point();
    m_timer->stop();
  }
}

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