Colormap renderer

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Apply a colormap renderer to a raster.

screenshot

Use case

A colormap renderer transforms pixel values in a raster to display raster data based on specific colors, aiding in visual analysis of the data. For example, a forestry commission may want to quickly visualize areas above and below the tree-line line occurring at a know elevation on a raster containing elevation values. They could overlay a transparent colormap set to color those areas below the tree-line elevation green, and those above white.

How to use the sample

Pan and zoom to explore the effect of the colormap applied to the raster.

How it works

  1. Create a Raster from a raster file.
  2. Create a RasterLayer from the raster.
  3. Create a QList<QColor>: colors at the beginning of the list replace the darkest values in the raster and colors at the end of the list replaced the brightest values of the raster.
  4. Create a colormap renderer with the color list and apply it to the raster layer with RasterLayer::setRenderer(RasterRenderer *renderer).

Relevant API

  • ColormapRenderer
  • Raster
  • RasterLayer

Offline Data

Read more about how to set up the sample's offline data here.

Link Local Location
ShastaBW.tif raster <userhome>/ArcGIS/Runtime/Data/raster/ShastaBW.tif

About the data

The raster used in this sample shows an area in the south of the Shasta-Trinity National Forest, California.

Tags

colormap, data, raster, renderer, visualization

Sample Code

RasterColormapRenderer.cppRasterColormapRenderer.cppRasterColormapRenderer.hRasterColormapRenderer.qml
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// [WriteFile Name=RasterColormapRenderer, Category=Layers]
// [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 "RasterColormapRenderer.h"

#include "ColormapRenderer.h"
#include "Map.h"
#include "MapQuickView.h"
#include "Raster.h"
#include "RasterLayer.h"

#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

RasterColormapRenderer::RasterColormapRenderer(QQuickItem* parent /* = nullptr */):
  QQuickItem(parent),
  m_dataPath(defaultDataPath() + "/ArcGIS/Runtime/Data/raster")
{
}

RasterColormapRenderer::~RasterColormapRenderer() = default;
void RasterColormapRenderer::init()
{
  // Register the map view for QML
  qmlRegisterType<MapQuickView>("Esri.Samples", 1, 0, "MapView");
  qmlRegisterType<RasterColormapRenderer>("Esri.Samples", 1, 0, "RasterColormapRendererSample");
}

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

  // find QML MapView component
  m_mapView = findChild<MapQuickView*>("mapView");
  m_mapView->setWrapAroundMode(WrapAroundMode::Disabled);

  //! [RasterColormapRenderer cpp add raster basemap]
  // Create the raster and raster layer
  Raster* raster = new Raster(m_dataPath + "/ShastaBW.tif", this);
  m_rasterLayer = new RasterLayer(raster, this);

  connect(m_rasterLayer, &RasterLayer::doneLoading, this, [this](Error error)
  {
    if (!error.isEmpty())
    {
      qDebug() << error.message() << error.additionalMessage();
      return;
    }

    m_mapView->setViewpointGeometry(m_rasterLayer->fullExtent(), 50);
  });

  ColormapRenderer* colormapRenderer = createRenderer();

  // set the colormap renderer on the raster layer
  m_rasterLayer->setRenderer(colormapRenderer);

  // Add the raster to the map as an operational layer
  Map* map = new Map(BasemapStyle::ArcGISImageryStandard, this);

  map->operationalLayers()->append(m_rasterLayer);

  m_mapView->setMap(map);
  //! [RasterColormapRenderer cpp add raster basemap]
}

ColormapRenderer *RasterColormapRenderer::createRenderer()
{
  // create a color map where values 0-150 are red and 150-250 are yellow
  QList<QColor> colors;
  colors.reserve(250);
  for (int i = 0; i < 250; ++i)
    colors.append( i < 150 ? Qt::red : Qt::yellow);

  // create a colormap renderer
  ColormapRenderer* colormapRenderer = new ColormapRenderer(colors, this);

  return colormapRenderer;
}

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