Densify and generalize

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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.

screenshot

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

  1. Use the static method GeometryEngine::densify(polyline, maxSegmentLength) to densify the polyline object. The resulting polyline object will have more points along the line, so that there are no points greater than maxSegmentLength from the next point.
  2. Use the static method GeometryEngine::generalize(polyline, maxDeviation, true) to generalize the polyline object. The resulting polyline object will have points shifted from the original 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 of a multipart geometry. This will have no effect in this sample as the polyline does not contain extraneous parts.
  3. Note that maxSegmentLength and maxDeviation are in the units of the geometry's coordinate system. In this example, a cartesian coordinate system is used and 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.cppDensifyAndGeneralize.cppDensifyAndGeneralize.hDensifyAndGeneralize.qml
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// [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]

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

#include "DensifyAndGeneralize.h"

#include "Map.h"
#include "MapQuickView.h"
#include "PointCollection.h"
#include "SpatialReference.h"
#include "Graphic.h"
#include "SimpleMarkerSymbol.h"
#include "SimpleLineSymbol.h"
#include "MultipointBuilder.h"
#include "PolylineBuilder.h"
#include "GeometryEngine.h"
#include "PointCollection.h"

using namespace Esri::ArcGISRuntime;

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

void DensifyAndGeneralize::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<DensifyAndGeneralize>("Esri.Samples", 1, 0, "DensifyAndGeneralizeSample");
}

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

  // find QML MapView component
  m_mapView = findChild<MapQuickView*>("mapView");

  // Create a map using the streets night vector basemap
  m_map = new Map(BasemapStyle::ArcGISStreetsNight, this);

  // Add a GraphicsOverlay
  m_graphicsOverlay = new GraphicsOverlay(this);
  m_mapView->graphicsOverlays()->append(m_graphicsOverlay);

  // Get Points along the river
  PointCollection* pointCollection = createPointCollection();

  // original multipart red graphic
  MultipointBuilder multipointBuilder(pointCollection->spatialReference());
  multipointBuilder.setPoints(pointCollection);
  SimpleMarkerSymbol* originalSms = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Circle, QColor("red"), 7.0f /*size*/, this);
  m_originalMultipointGraphic = new Graphic(multipointBuilder.toGeometry(), originalSms, this);
  m_originalMultipointGraphic->setZIndex(0);
  m_graphicsOverlay->graphics()->append(m_originalMultipointGraphic);

  // original red dotted line graphic
  PolylineBuilder polylineBuilder(pointCollection->spatialReference());
  const int pointCollectionSize = pointCollection->size();
  for (int i = 0; i < pointCollectionSize; i++)
  {
    polylineBuilder.addPoint(pointCollection->point(i));
  }
  SimpleLineSymbol* originalSls = new SimpleLineSymbol(SimpleLineSymbolStyle::Dot, QColor("red"), 3.0f /*size*/, this);
  m_originalLineGraphic = new Graphic(polylineBuilder.toGeometry(), originalSls, this);
  m_originalLineGraphic->setZIndex(1);
  m_graphicsOverlay->graphics()->append(m_originalLineGraphic);

  // resulting (densified and generalized) multipart magenta graphic
  SimpleMarkerSymbol* resultSms = new SimpleMarkerSymbol(SimpleMarkerSymbolStyle::Circle, QColor("magenta"), 7.0f /*size*/, this);
  m_resultMultipointGraphic = new Graphic(this);
  m_resultMultipointGraphic->setSymbol(resultSms);
  m_resultMultipointGraphic->setZIndex(2);
  m_graphicsOverlay->graphics()->append(m_resultMultipointGraphic);

  // resulting (densified and generalized) multipart magenta graphic
  SimpleLineSymbol* resultSls = new SimpleLineSymbol(SimpleLineSymbolStyle::Solid, QColor("magenta"), 3.0f /*size*/, this);
  m_resultLineGraphic = new Graphic(this);
  m_resultLineGraphic->setSymbol(resultSls);
  m_resultLineGraphic->setZIndex(3);
  m_graphicsOverlay->graphics()->append(m_resultLineGraphic);

  // Set map to map view
  m_mapView->setMap(m_map);

  // set viewpoint
  m_mapView->setViewpointGeometry(m_originalMultipointGraphic->geometry().extent(), 100);
}

void DensifyAndGeneralize::updateGeometry(bool densify, double maxSegmentLength, bool generalize, double maxDeviation)
{
  if (!m_originalLineGraphic)
    return;

  // Get the initial Geometry
  Polyline polyline = m_originalLineGraphic->geometry();
  if (polyline.isEmpty())
    return;

  // Generalize the polyline
  if (generalize)
    polyline = GeometryEngine::generalize(polyline, maxDeviation, true);

  // Densify the polyline
  if (densify)
    polyline = GeometryEngine::densify(polyline, maxSegmentLength);

  // Update the line graphic
  m_resultLineGraphic->setGeometry(polyline);

  // Update the multipoint graphic
  if (polyline.parts().size() < 1)
    return;

  MultipointBuilder multipointBuilder(polyline.spatialReference());
  PointCollection* pointCollection = new PointCollection(polyline.spatialReference(), this);

  ImmutablePointCollection polylinePoints = polyline.parts().part(0).points();
  const int polylinePointsSize = polylinePoints.size();
  for (int i = 0; i < polylinePointsSize; i++)
  {
    pointCollection->addPoint(polylinePoints.point(i));
  }
  multipointBuilder.setPoints(pointCollection);
  m_resultMultipointGraphic->setGeometry(multipointBuilder.toGeometry());
}

PointCollection* DensifyAndGeneralize::createPointCollection()
{
  SpatialReference sr(32126);
  PointCollection* pointCollection = new PointCollection(sr, this);
  pointCollection->addPoint(2330611.130549, 202360.002957, 0.000000);
  pointCollection->addPoint(2330583.834672, 202525.984012, 0.000000);
  pointCollection->addPoint(2330574.164902, 202691.488009, 0.000000);
  pointCollection->addPoint(2330689.292623, 203170.045888, 0.000000);
  pointCollection->addPoint(2330696.773344, 203317.495798, 0.000000);
  pointCollection->addPoint(2330691.419723, 203380.917080, 0.000000);
  pointCollection->addPoint(2330435.065296, 203816.662457, 0.000000);
  pointCollection->addPoint(2330369.500800, 204329.861789, 0.000000);
  pointCollection->addPoint(2330400.929891, 204712.129673, 0.000000);
  pointCollection->addPoint(2330484.300447, 204927.797132, 0.000000);
  pointCollection->addPoint(2330514.469919, 205000.792463, 0.000000);
  pointCollection->addPoint(2330638.099138, 205271.601116, 0.000000);
  pointCollection->addPoint(2330725.315888, 205631.231308, 0.000000);
  pointCollection->addPoint(2330755.640702, 206433.354860, 0.000000);
  pointCollection->addPoint(2330680.644719, 206660.240923, 0.000000);
  pointCollection->addPoint(2330386.957926, 207340.947204, 0.000000);
  pointCollection->addPoint(2330485.861737, 207742.298501, 0.000000);
  return pointCollection;
}

void DensifyAndGeneralize::showResults(bool show)
{
  m_resultMultipointGraphic->setVisible(show);
  m_resultLineGraphic->setVisible(show);
}

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