Get elevation at point

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Sample viewer app

Get the elevation for a given point on a surface.

screenshot

Use case

Knowing the elevation at a given point in a landscape can aid in navigation, planning and survey in the field.

How to use the sample

Click anywhere on the surface to get the elevation at that point.

How it works

  1. Create a SceneView and Scene with an imagery base map.
  2. Set an ArcGISTiledElevationSource as the elevation source of the scene's base surface.
  3. Use the screenToBaseSurface(screenPoint) method on the scene view to convert the clicked screen point into a point on surface.
  4. Use the locationToElevation(surfacePoint) method on the base surface to asynchronously get the elevation.

Relevant API

  • ArcGISTiledElevationSource
  • BaseSurface
  • ElevationSourceListModel
  • SceneView

Additional information

Calling locationToElevation(surfacePoint) retrieves the most accurate available elevation value at a given point which requires it to go to the server or local raster file and load the highest level of detail of data for the target location and return the elevation value.

If multiple elevation sources are present in the surface the top most visible elevation source with a valid elevation in the given location is used to determine the result.

Tags

elevation, MapViews SceneViews and UI, surface

Sample Code

GetElevationAtPoint.cppGetElevationAtPoint.cppGetElevationAtPoint.hGetElevationAtPoint.qml
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// [WriteFile Name=GetElevationAtPoint, Category=Scenes]
// [Legal]
// Copyright 2019 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 "GetElevationAtPoint.h"

#include "ArcGISTiledElevationSource.h"
#include "GraphicsOverlay.h"
#include "Scene.h"
#include "SceneQuickView.h"
#include "SimpleMarkerSymbol.h"
#include "Surface.h"

using namespace Esri::ArcGISRuntime;

GetElevationAtPoint::GetElevationAtPoint(QObject* parent /* = nullptr */):
  QObject(parent),
  m_scene(new Scene(BasemapStyle::ArcGISImageryStandard, this)),
  m_graphicsOverlay(new GraphicsOverlay(this)),
  m_elevationMarker(new Graphic(Geometry(), new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Circle, QColor("red"), 12, this), this))
{
  // create a new elevation source from Terrain3D REST service
  ArcGISTiledElevationSource* elevationSource = new ArcGISTiledElevationSource(
        QUrl("https://elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer"), this);

  // add the elevation source to the scene to display elevation
  m_scene->baseSurface()->elevationSources()->append(elevationSource);

  // Set the marker to be invisible initially, will be flaggd visible when user interacts with scene for the first time, to visualise clicked position
  m_elevationMarker->setVisible(false);

  // Add the marker to the graphics overlay so it will be displayed. Graphics overlay is attached to the sceneView in ::setSceneView()
  m_graphicsOverlay->graphics()->append(m_elevationMarker);
}

GetElevationAtPoint::~GetElevationAtPoint() = default;

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

SceneQuickView* GetElevationAtPoint::sceneView() const
{
  return m_sceneView;
}

// Set the view (created in QML)
void GetElevationAtPoint::setSceneView(SceneQuickView* sceneView)
{
  if (!sceneView || sceneView == m_sceneView)
  {
    return;
  }

  m_sceneView = sceneView;
  m_sceneView->setArcGISScene(m_scene);

  // Create a camera, looking at the Himalayan mountain range.
  constexpr double latitude = 28.4;
  constexpr double longitude = 83.9;
  constexpr double altitude = 10000.0;
  constexpr double heading = 10.0;
  constexpr double pitch = 80.0;
  constexpr double roll = 0.0;
  Camera camera(latitude, longitude, altitude, heading, pitch, roll);

  // Set the sceneview to use above camera, waits for load so scene is immediately displayed in appropriate place.
  m_sceneView->setViewpointCameraAndWait(camera);

  // Append the graphics overlays to the sceneview, so we can visualise elevation on click
  m_sceneView->graphicsOverlays()->append(m_graphicsOverlay);

  // Hook up clicks into the 3d scene to below behaviour that displays marker & elevation value.
  connect(sceneView, &SceneQuickView::mouseClicked, this, &GetElevationAtPoint::displayElevationOnClick);

  emit sceneViewChanged();
}

void GetElevationAtPoint::displayElevationOnClick(QMouseEvent& mouseEvent)
{
  // Convert clicked screen position to position on the map surface.
  const Point baseSurfacePos = m_sceneView->screenToBaseSurface(mouseEvent.x(), mouseEvent.y());

  // Connect to callback for elevation query, which places marker and sets elevation
  connect(m_scene->baseSurface(), &Surface::locationToElevationCompleted,
          this, [baseSurfacePos, this](QUuid /*taskId*/, double elevation)
  {
    // Place the elevation marker circle at the clicked position
    m_elevationMarker->setGeometry(baseSurfacePos);
    m_elevationMarker->setVisible(true);

    // Assign the elevation value. UI is bound to this value, so it updates to display new elevation.
    m_elevation = elevation;

    // Notify of property changes
    emit elevationChanged(elevation);
    emit elevationQueryRunningChanged();
  });

  //Invoke get elevation query
  m_elevationQueryTaskWatcher = m_scene->baseSurface()->locationToElevation(baseSurfacePos);
  emit elevationQueryRunningChanged();
}

double GetElevationAtPoint::elevation() const
{
  return m_elevation;
}

bool GetElevationAtPoint::elevationQueryRunning() const
{
  return !(m_elevationQueryTaskWatcher.isDone() || m_elevationQueryTaskWatcher.isCanceled());
}

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