Colormap renderer

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Apply a colormap renderer to a raster.

Colormap renderer

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 occurring at a known 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 an AGSRaster from a the provided resource, ShastaBW.tif.
  2. Create an AGSRasterLayer from the raster.
  3. Create an array of 250 colors to represent the possible values from the raster. 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 an AGSColormapRenderer with the color array and apply it to the raster layer.

Relevant API

  • AGSColormapRenderer
  • AGSRaster
  • AGSRasterLayer

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

ColormapRendererViewController.swift
                                                              
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//
// 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.

import UIKit
import ArcGIS

class ColormapRendererViewController: UIViewController {
    @IBOutlet var mapView: AGSMapView! {
        didSet {
            // Assign map to the map view.
            mapView.map = AGSMap(basemapStyle: .arcGISImageryStandard)

            // Create and add the raster layer to the operational layers of the map.
            mapView.map?.operationalLayers.add(makeRasterLayer())
        }
    }

    private func makeRasterLayer() -> AGSRasterLayer {
        let raster = AGSRaster(name: "ShastaBW", extension: "tif")

        // Create raster layer using raster.
        let rasterLayer = AGSRasterLayer(raster: raster)

        // Make two arrays to represent two different colors then appened them together.
        let colors = Array(repeating: UIColor.red, count: 150) + Array(repeating: UIColor.yellow, count: 151)

        // Render the colormap using the array of colors.
        let colormapRenderer = AGSColormapRenderer(colors: colors)
        rasterLayer.renderer = colormapRenderer

        // Set map view's viewpoint to the raster layer's full extent.
        rasterLayer.load { [weak self] (error) in
            if let error = error {
                self?.presentAlert(error: error)
            } else {
                if let center = rasterLayer.fullExtent?.center {
                    self?.mapView.setViewpoint(AGSViewpoint(center: center, scale: 80000))
                }
            }
        }
        return rasterLayer
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // Add the source code button item to the right of navigation bar.
        (self.navigationItem.rightBarButtonItem as! SourceCodeBarButtonItem).filenames = ["ColormapRendererViewController"]
    }
}

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