Apply mosaic rule to rasters

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Apply mosaic rule to a mosaic dataset of rasters.

Apply mosaic rule to rasters

Use case

An image service can use a mosaic rule to mosaic multiple rasters on-the-fly. A mosaic rule can specify which rasters are selected, and how the selected rasters are z-ordered. It can also specify how overlapping pixels from different rasters at the same location are resolved.

For example, when using the "ByAttribute" mosaic method, the values in an attribute field are used to sort the images, and when using the "Center" method, the image closest to the center of the display is positioned as the top image in the mosaic. Additionally, the mosaic operator allows you to define how to resolve the overlapping cells, such as choosing a blending operation.

Specifying mosaic rules is useful for viewing overlapping rasters. For example, using the "ByAttribute" mosaic method to sort the rasters based on their acquisition date allows the newest image to be on top. Using "Mean" mosaic operation makes the overlapping areas contain the mean cell values from all the overlapping rasters.

How to use the sample

When the rasters are loaded, choose from a list of preset mosaic rules to apply to the rasters.

How it works

  1. Create an ImageServiceRaster using the service's URL.
  2. Create a MosaicRule object and set it to the MosaicRule property of the image service raster, if it does not specify a mosaic rule.
  3. Create a RasterLayer from the image service raster and add it to the map.
  4. Set the MosaicMethod, MosaicOperation, and other properties of the mosaic rule object accordingly to specify the rule on the raster dataset.

Relevant API

  • ImageServiceRaster
  • MosaicMethod
  • MosaicOperation
  • MosaicRule

About the data

This sample uses a raster image service hosted on ArcGIS Online that shows aerial images of Amberg, Germany.

Additional information

For more information, see Understanding the mosaicking rules from ArcGIS Desktop documentation. To learn more about how to define certain mosaic rules, see Mosaic rule objects from ArcGIS for Developers.

Tags

image service, mosaic method, mosaic rule, raster

Sample Code

ApplyMosaicRule.cs
                                                                                                                                                                      
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// Copyright 2021 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 ArcGISRuntime;
using Esri.ArcGISRuntime.Mapping;
using Esri.ArcGISRuntime.Rasters;
using Esri.ArcGISRuntime.UI.Controls;
using Foundation;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using UIKit;

namespace ArcGISRuntimeXamarin.Samples.ApplyMosaicRule
{
    [Register("ApplyMosaicRule")]
    [ArcGISRuntime.Samples.Shared.Attributes.Sample(
        name: "Apply mosaic rule to rasters",
        category: "Layers",
        description: "Apply mosaic rule to a mosaic dataset of rasters.",
        instructions: "When the rasters are loaded, choose from a list of preset mosaic rules to apply to the rasters.",
        tags: new[] { "image service", "mosaic method", "mosaic rule", "raster" })]
    public class ApplyMosaicRule : UIViewController
    {
        // Hold references to UI controls.
        private MapView _myMapView;
        private UIButton _rulePickerButton;

        private ImageServiceRaster _imageServiceRaster;

        // Different mosaic rules to use with the image service raster.
        private Dictionary<string, MosaicRule> _mosaicRules = new Dictionary<string, MosaicRule>
        {
            { "None", new MosaicRule { MosaicMethod = MosaicMethod.None} },
            { "Northwest", new MosaicRule { MosaicMethod = MosaicMethod.Northwest, MosaicOperation = MosaicOperation.First} },
            { "Center", new MosaicRule { MosaicMethod = MosaicMethod.Center, MosaicOperation = MosaicOperation.Blend} },
            { "ByAttribute", new MosaicRule { MosaicMethod = MosaicMethod.Attribute, SortField = "OBJECTID"} },
            { "LockRaster", new MosaicRule { MosaicMethod = MosaicMethod.LockRaster, LockRasterIds = { 1, 7, 12 } } },
        };

        public ApplyMosaicRule()
        {
            Title = "Apply mosaic rule to rasters";
        }

        private async Task Initialize()
        {
            // Create a raster layer using an image service.
            _imageServiceRaster = new ImageServiceRaster(new Uri("https://sampleserver7.arcgisonline.com/server/rest/services/amberg_germany/ImageServer"));
            RasterLayer rasterLayer = new RasterLayer(_imageServiceRaster);
            await rasterLayer.LoadAsync();

            // Create a map with the raster layer.
            _myMapView.Map = new Map(BasemapStyle.ArcGISTopographic);
            _myMapView.Map.OperationalLayers.Add(rasterLayer);
            await _myMapView.SetViewpointAsync(new Viewpoint(rasterLayer.FullExtent));

            // Populate the combo box.
            _imageServiceRaster.MosaicRule = _mosaicRules["None"];
            _rulePickerButton.SetTitle("Rule: None", UIControlState.Normal);
        }

        private void ChangeMosaicRule(object sender, EventArgs e)
        {
            // Start the UI for the user choosing the trace type.
            UIAlertController prompt = UIAlertController.Create(null, "Choose mosaic rule", UIAlertControllerStyle.ActionSheet);

            // Add a selection action for every valid trace type.
            foreach (string name in _mosaicRules.Keys)
            {
                prompt.AddAction(UIAlertAction.Create(name, UIAlertActionStyle.Default, RuleClick));
            }

            // Needed to prevent crash on iPad.
            UIPopoverPresentationController ppc = prompt.PopoverPresentationController;
            if (ppc != null)
            {
                ppc.SourceView = _rulePickerButton;
                ppc.PermittedArrowDirections = UIPopoverArrowDirection.Down;
            }

            PresentViewController(prompt, true, null);
        }

        private void RuleClick(UIAlertAction action)
        {
            // Change the mosaic rule used for the image service raster.
            _imageServiceRaster.MosaicRule = _mosaicRules[action.Title];
            _rulePickerButton.SetTitle($"Rule: {action.Title}", UIControlState.Normal);
        }

        public override void LoadView()
        {
            // Create the views.
            View = new UIView() { BackgroundColor = ApplicationTheme.BackgroundColor };

            _myMapView = new MapView();
            _myMapView.TranslatesAutoresizingMaskIntoConstraints = false;

            UILabel instructions = new UILabel
            {
                Text = "Choose a mosaic rule to apply to the image service.",
                AdjustsFontSizeToFitWidth = true,
                TextAlignment = UITextAlignment.Center,
                BackgroundColor = UIColor.FromWhiteAlpha(0, .6f),
                TextColor = UIColor.White,
                Lines = 1,
                TranslatesAutoresizingMaskIntoConstraints = false
            };

            _rulePickerButton = new UIButton(UIButtonType.System);
            _rulePickerButton.TranslatesAutoresizingMaskIntoConstraints = false;

            // Add the views.
            View.AddSubviews(_myMapView, instructions, _rulePickerButton);

            // Lay out the views.
            NSLayoutConstraint.ActivateConstraints(new[]
                {
                    _myMapView.TopAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.TopAnchor),
                    _myMapView.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                    _myMapView.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                    _myMapView.BottomAnchor.ConstraintEqualTo(_rulePickerButton.TopAnchor),

                    _rulePickerButton.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                    _rulePickerButton.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                    _rulePickerButton.BottomAnchor.ConstraintEqualTo(View.SafeAreaLayoutGuide.BottomAnchor),
                    _rulePickerButton.HeightAnchor.ConstraintEqualTo(40),

                    instructions.TopAnchor.ConstraintEqualTo(_myMapView.TopAnchor),
                    instructions.LeadingAnchor.ConstraintEqualTo(View.LeadingAnchor),
                    instructions.TrailingAnchor.ConstraintEqualTo(View.TrailingAnchor),
                    instructions.HeightAnchor.ConstraintEqualTo(40),
                }
            );
        }

        public override void ViewWillAppear(bool animated)
        {
            base.ViewWillAppear(animated);

            // Subscribe to events.
            _rulePickerButton.TouchUpInside += ChangeMosaicRule;
        }

        public override void ViewDidDisappear(bool animated)
        {
            base.ViewDidDisappear(animated);

            // Unsubscribe from events, per best practice.
            _rulePickerButton.TouchUpInside -= ChangeMosaicRule;
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            _ = Initialize();
        }
    }
}

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