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ArcGIS Runtime SDK for .NET

Stretch renderer

This code sample is available for these platforms:
View Sample on GitHub

Use a stretch renderer to enhance the visual contrast of raster data for analysis.

Image of stretch renderer

Use case

An appropriate stretch renderer can enhance the contrast of raster imagery, allowing the user to control how their data is displayed for efficient imagery analysis.

How to use the sample

Choose one of the stretch parameter types:

  • Standard deviation - a linear stretch defined by the standard deviation of the pixel values
  • Min-max - a linear stretch based on minimum and maximum pixel values
  • Percent clip - a linear stretch between the defined percent clip minimum and percent clip maximum pixel values

Then configure the parameters and tap 'Update renderer'.

How it works

  1. Create a Raster from a raster file.
  2. Create a RasterLayer from the Raster.
  3. Add the layer to the map.
  4. Create a StretchRenderer, specifying the stretch parameters and other properties.
  5. Apply the Renderer to the raster layer.

Relevant API

  • ColorRamp
  • MinMaxStretchParameters
  • PercentClipStretchParameters
  • Raster
  • RasterLayer
  • StandardDeviationStretchParameters
  • StretchParameters
  • StretchRenderer

Offline data

This sample downloads the following items from ArcGIS Online automatically:

About the data

This sample uses a raster imagery tile of an area of forested mountainous terrain and rivers.

Additional information

See Stretch function in the ArcMap documentation for more information about the types of stretches that can be performed.

Tags

analysis, deviation, histogram, imagery, interpretation, min-max, percent clip, pixel, raster, stretch, symbology, visualization

Sample Code

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:esriUI="clr-namespace:Esri.ArcGISRuntime.Xamarin.Forms;assembly=Esri.ArcGISRuntime.Xamarin.Forms"
             x:Class="ArcGISRuntime.Samples.ChangeStretchRenderer.ChangeStretchRenderer"
             Title="Stretch renderer">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="40"/>
            <RowDefinition Height="100" />
            <RowDefinition Height="40" />
            <RowDefinition Height="40"/>
            <RowDefinition Height="40"/>
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Label Grid.Row="0">Choose a stretch renderer type from the listbox, adjust the parameter values, then click the 'Update Renderer' button.</Label>
        <ListView Grid.Row="1" x:Name="RendererTypes" ItemSelected="RendererTypes_SelectionChanged"/>
        <StackLayout Orientation="Horizontal" Grid.Row="2">
            <Label x:Name="Label_Parameter1" Text="Parameter1" />
            <Entry x:Name="Input_Parameter1" Text="EnterValue1" />
        </StackLayout>
        <StackLayout Orientation="Horizontal" Grid.Row="3">
            <Label x:Name="Label_Parameter2" Text="Parameter2" />
            <Entry x:Name="Input_Parameter2" Text="EnterValue2" />
        </StackLayout>
        <Button Grid.Row="4" x:Name="UpdateRenderer" Clicked="OnUpdateRendererClicked" Text="Update Renderer" />
        <esriUI:MapView Grid.Row="5" x:Name="MyMapView" />
    </Grid>
</ContentPage>
// 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.

using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Rasters;
using ArcGISRuntime.Samples.Managers;
using System;
using Xamarin.Forms;
using System.Collections.ObjectModel;
using System.Collections.Generic;

namespace ArcGISRuntime.Samples.ChangeStretchRenderer
{
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Stretch renderer",
        category: "Layers",
        description: "Use a stretch renderer to enhance the visual contrast of raster data for analysis.",
        instructions: "Choose one of the stretch parameter types:",
        tags: new[] { "analysis", "deviation", "histogram", "imagery", "interpretation", "min-max", "percent clip", "pixel", "raster", "stretch", "symbology", "visualization" })]
	[ArcGISRuntime.Samples.Shared.Attributes.OfflineData("95392f99970d4a71bd25951beb34a508")]
    public partial class ChangeStretchRenderer : ContentPage
    {
        public ChangeStretchRenderer()
        {
            InitializeComponent();

            // Call a function to set up the map
            Initialize();
        }

        private async void Initialize()
        {
            // Initialize the GUI controls appearance
            ObservableCollection<string> myObservableCollection_RendererTypes = new ObservableCollection<string>();
            myObservableCollection_RendererTypes.Add("Min Max");
            myObservableCollection_RendererTypes.Add("Percent Clip");
            myObservableCollection_RendererTypes.Add("Standard Deviation");
            RendererTypes.ItemsSource = myObservableCollection_RendererTypes;
            RendererTypes.SelectedItem = "Min Max";

            // Add an imagery basemap
            MyMapView.Map = new Map(Basemap.CreateImagery());

            // Get the file name
            string filepath = GetRasterPath();

            // Load the raster file
            Raster myRasterFile = new Raster(filepath);

            // Create the layer
            RasterLayer myRasterLayer = new RasterLayer(myRasterFile);

            // Add the layer to the map
            MyMapView.Map.OperationalLayers.Add(myRasterLayer);

            try
            {
                // Wait for the layer to load
                await myRasterLayer.LoadAsync();

                // Set the viewpoint
                await MyMapView.SetViewpointGeometryAsync(myRasterLayer.FullExtent);
            }
            catch (Exception e)
            {
                await Application.Current.MainPage.DisplayAlert("Error", e.ToString(), "OK");
            }
        }

        private void RendererTypes_SelectionChanged(object sender, SelectedItemChangedEventArgs e)
        {
            // Get the user choice for the raster stretch render
            string myRendererTypeChoice = e.SelectedItem.ToString();

            switch (myRendererTypeChoice)
            {
                case "Min Max":

                    // This section displays/resets the user choice options for MinMaxStretchParameters

                    // Make sure all the GUI items are visible
                    Label_Parameter1.IsVisible = true;
                    Label_Parameter2.IsVisible = true;
                    Input_Parameter1.IsVisible = true;
                    Input_Parameter2.IsVisible = true;

                    // Define what values/options the user sees
                    Label_Parameter1.Text = "Minimum value (0 - 255):";
                    Label_Parameter2.Text = "Maximum value (0 - 255):";
                    Input_Parameter1.Text = "10";
                    Input_Parameter2.Text = "150";

                    break;

                case "Percent Clip":

                    // This section displays/resets the user choice options for PercentClipStretchParameters

                    // Make sure all the GUI items are visible
                    Label_Parameter1.IsVisible = true;
                    Label_Parameter2.IsVisible = true;
                    Input_Parameter1.IsVisible = true;
                    Input_Parameter2.IsVisible = true;

                    // Define what values/options the user sees
                    Label_Parameter1.Text = "Minimum (0 - 100):";
                    Label_Parameter2.Text = "Maximum (0 - 100)";
                    Input_Parameter1.Text = "0";
                    Input_Parameter2.Text = "50";

                    break;

                case "Standard Deviation":

                    // This section displays/resets the user choice options for StandardDeviationStretchParameters

                    // Make sure that only the necessary GUI items are visible
                    Label_Parameter1.IsVisible = true;
                    Label_Parameter2.IsVisible = false;
                    Input_Parameter1.IsVisible = true;
                    Input_Parameter2.IsVisible = false;

                    // Define what values/options the user sees
                    Label_Parameter1.Text = "Factor (.25 to 4):";
                    Input_Parameter1.Text = "0.5";

                    break;
            }
        }

        private void OnUpdateRendererClicked(object sender, EventArgs e)
        {
            // Convert the input text to doubles and return if they're invalid.
            double input1;
            double input2;
            try
            {
                input1 = Convert.ToDouble(Input_Parameter1.Text);
                input2 = Convert.ToDouble(Input_Parameter2.Text);
            }
            catch (Exception ex)
            {
                Application.Current.MainPage.DisplayAlert("Alert", ex.Message, "OK");
                return;
            }

            // Get the user choice for the raster stretch render
            string myRendererTypeChoice = RendererTypes.SelectedItem.ToString();

            // Create an IEnumerable from an empty list of doubles for the gamma values in the stretch render
            IEnumerable<double> myGammaValues = new List<double>();

            // Create a color ramp for the stretch renderer
            ColorRamp myColorRamp = ColorRamp.Create(PresetColorRampType.DemLight, 1000);

            // Create the place holder for the stretch renderer
            StretchRenderer myStretchRenderer = null;

            switch (myRendererTypeChoice)
            {
                case "Min Max":

                    // This section creates a stretch renderer based on a MinMaxStretchParameters
                    // TODO: Add you own logic to ensure that accurate min/max stretch values are used

                    // Create an IEnumerable from a list of double min stretch value doubles
                    IEnumerable<double> myMinValues = new List<double> { input1 };

                    // Create an IEnumerable from a list of double max stretch value doubles
                    IEnumerable<double> myMaxValues = new List<double> { input2 };

                    // Create a new MinMaxStretchParameters based on the user choice for min and max stretch values
                    MinMaxStretchParameters myMinMaxStretchParameters = new MinMaxStretchParameters(myMinValues, myMaxValues);

                    // Create the stretch renderer based on the user defined min/max stretch values, empty gamma values, statistic estimates, and a predefined color ramp 
                    myStretchRenderer = new Esri.ArcGISRuntime.Rasters.StretchRenderer(myMinMaxStretchParameters, myGammaValues, true, myColorRamp);

                    break;

                case "Percent Clip":

                    // This section creates a stretch renderer based on a PercentClipStretchParameters
                    // TODO: Add you own logic to ensure that accurate min/max percent clip values are used

                    // Create a new PercentClipStretchParameters based on the user choice for min and max percent clip values
                    PercentClipStretchParameters myPercentClipStretchParameters = new PercentClipStretchParameters(input1, input2);

                    // Create the percent clip renderer based on the user defined min/max percent clip values, empty gamma values, statistic estimates, and a predefined color ramp 
                    myStretchRenderer = new StretchRenderer(myPercentClipStretchParameters, myGammaValues, true, myColorRamp);

                    break;

                case "Standard Deviation":

                    // This section creates a stretch renderer based on a StandardDeviationStretchParameters
                    // TODO: Add you own logic to ensure that an accurate standard deviation value is used

                    // Create a new StandardDeviationStretchParameters based on the user choice for standard deviation value
                    StandardDeviationStretchParameters myStandardDeviationStretchParameters = new StandardDeviationStretchParameters(input1);

                    // Create the standard deviation renderer based on the user defined standard deviation value, empty gamma values, statistic estimates, and a predefined color ramp 
                    myStretchRenderer = new StretchRenderer(myStandardDeviationStretchParameters, myGammaValues, true, myColorRamp);

                    break;
            }

            // Get the existing raster layer in the map
            RasterLayer myRasterLayer = (RasterLayer)MyMapView.Map.OperationalLayers[0];

            // Apply the stretch renderer to the raster layer
            myRasterLayer.Renderer = myStretchRenderer;
        }

        private static string GetRasterPath()
        {
            return DataManager.GetDataFolder("95392f99970d4a71bd25951beb34a508", "shasta", "ShastaBW.tif");
        }

    }
}