Display a viewshed

Viewshed analysis determines the visibility of terrain, buildings, and other 3D objects from an observer's location within a scene (using a specified field of view). The result indicates which areas are visible and which are obstructed when viewed from the observer's perspective.

In this tutorial, you will perform and display a viewshed analysis in a web scene. Your viewshed analysis will show visibility (visible or obstructed) and can be used to determine which hotspots in the Yosemite Valley are visible from a specified observer's perspective.

Prerequisites

Steps

Open an Android Studio project

1. To start this tutorial, complete the Display a scene tutorial, or download and unzip the Display a scene solution in a new folder.

2. Modify the old project for use in this new tutorial.

   Expand for detailed instructions

   1. On your file system, delete the .idea folder, if present, at the top level of your project.

   2. In the Android view, open app > res > values > strings.xml.

      In the <string name="app_name"> element, change the text content to Display a viewshed.

      strings.xml

      Use dark colors for code blocks

      1
      2
      3
      <resources>
          <string name="app_name">Display a viewshed</string>
      </resources>

   3. In the Android view, open Gradle Scripts > settings.gradle.kts.

      Change the value of rootProject.name to "Display a viewshed".

      settings.gradle.kts

      Expand

      Use dark colors for code blocks

      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21
      22
      23
      24
      25
      26
      dependencyResolutionManagement {
          repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
          repositories {
              google()
              mavenCentral()
              maven { url = uri("https://esri.jfrog.io/artifactory/arcgis") }
          }
      }
      
      rootProject.name = "Display a viewshed"
      include(":app")

   4. The UI theme composable in Display a map tutorial was DisplayAMapTheme. Rename the theme composable throughout the tutorial by refactoring DisplayAMapTheme.

      In the Android view, open app > kotlin+java > com.exmple.app > ui.theme > Theme.kt.

      Right-click the function name DisplayAMapTheme and select Refactor -> Rename. Replace the name with DisplayAViewshedTheme.

      Theme.kt

      Use dark colors for code blocksCopy

      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21
      22
      23
      24
      25
      26
      27
      28
      29
      30
      31
      32
      33
      34
      35
      36
      37
      38
      39
      40
      41
      42
      43
      44
      45
      46
      47
      48
      49
      50
      51
      52
      53
      54
      55
      56
      57
      58
      59
      60
      @Composable
      fun DisplayAMapTheme(
      
          darkTheme: Boolean = isSystemInDarkTheme(),
          // Dynamic color is available on Android 12+
          dynamicColor: Boolean = true,
          content: @Composable () -> Unit
      ) {
          val colorScheme = when {
              dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
                  val context = LocalContext.current
                  if (darkTheme) dynamicDarkColorScheme(context) else dynamicLightColorScheme(context)
              }
      
              darkTheme -> DarkColorScheme
              else -> LightColorScheme
          }
      

   5. Click File > Sync Project with Gradle files. Android Studio will recognize your changes and create a new .idea folder.

3. If you downloaded the solution, get an access token and set the API key in MainActivity.kt.

   Instructions to set the API Key

   An API Key gives your app access to secure resources used in this tutorial.

   1. Go to the Create an API key tutorial to obtain a new API key access token using your ArcGIS Location Platform or ArcGIS Online account. Ensure that the following privilege is enabled: Location services > Basemaps > Basemap styles service. Copy the access token as it will be used in the next step.

   2. In Android Studio: in the Android view, open app > java > com.example.app > MainActivity.

   3. In the setApiKey() function, find the ApiKey.create() call and paste your access token inside the double quotes, replacing YOUR_ACCESS_TOKEN.

      MainActivity.kt

      Use dark colors for code blocksCopy

      1
      2
      3
      4
      5
      6
      7
      8
      9
      10
      11
      12
      13
      14
      15
      16
      17
      18
      19
      20
      21
      22
      23
      24
      25
      26
      27
      28
      29
      30
      31
      32
      33
      34
          private fun setApiKey() {
      
              ArcGISEnvironment.apiKey = ApiKey.create("YOUR_ACCESS_TOKEN")
      
          }
      

4. In libs.versions.toml, add a [libraries] entry for the dependency. In the module-level build.gradle.kts (app), add the dependency for the lifecycle view model.

   libs.versions.tomlbuild.gradle.kts (:app)
   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   [libraries]
   arcgis-maps-kotlin = { group = "com.esri", name = "arcgis-maps-kotlin", version.ref = "arcgisMapsKotlin" }
   arcgis-maps-kotlin-toolkit-bom = { group = "com.esri", name = "arcgis-maps-kotlin-toolkit-bom", version.ref = "arcgisMapsKotlin" }
   arcgis-maps-kotlin-toolkit-geoview-compose = { group = "com.esri", name = "arcgis-maps-kotlin-toolkit-geoview-compose" }
   # Additional modules from Toolkit, if needed, such as:
   # arcgis-maps-kotlin-toolkit-authentication = { group = "com.esri", name = "arcgis-maps-kotlin-toolkit-authentication" }
   
   androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }
   junit = { group = "junit", name = "junit", version.ref = "junit" }
   androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "junitVersion" }
   androidx-espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version.ref = "espressoCore" }
   androidx-lifecycle-runtime-ktx = { group = "androidx.lifecycle", name = "lifecycle-runtime-ktx", version.ref = "lifecycleRuntimeKtx" }
   
   androidx-lifecycle-viewmodel-compose = { group = "androidx.lifecycle", name = "lifecycle-viewmodel-compose", version.ref = "lifecycleRuntimeKtx" }
   

   Expand

Add imports

Modify import statements to reference the packages and classes required for this tutorial.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160

@file:OptIn(ExperimentalMaterial3Api::class)

package com.example.app.screens

import android.util.Log
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.Scaffold
import androidx.compose.material3.Slider
import androidx.compose.material3.Text
import androidx.compose.material3.TextButton
import androidx.compose.material3.TopAppBar
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableFloatStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.res.stringResource
import androidx.compose.ui.unit.dp
import androidx.lifecycle.ViewModel
import androidx.lifecycle.viewModelScope
import androidx.lifecycle.viewmodel.compose.viewModel
import com.arcgismaps.analysis.LocationViewshed
import com.arcgismaps.geometry.Point
import com.arcgismaps.mapping.ArcGISScene
import com.arcgismaps.mapping.PortalItem
import com.arcgismaps.mapping.view.AnalysisOverlay
import com.arcgismaps.mapping.view.ScreenCoordinate
import com.arcgismaps.portal.Portal
import com.arcgismaps.toolkit.geoviewcompose.SceneView
import com.arcgismaps.toolkit.geoviewcompose.SceneViewProxy
import com.example.app.R
import kotlinx.coroutines.launch
import kotlin.math.roundToInt

Get the web scene item ID

You can use ArcGIS tools to create and view web scenes. Use the Scene Viewer to identify the web scene item ID. This item ID will be used later in the tutorial.

1. Go to the Yosemite Valley Hotspots web scene in the Scene Viewer in ArcGIS Online. This web scene displays terrain and hotspots in the Yosemite Valley.
2. Make a note of the item ID at the end of the browser's URL. The item ID should be 7558ee942b2547019f66885c44d4f0b1.

Create a view model

Modern app architecture uses a map view model to hold the business logic and the mutual state of your app.

1. In Android Studio: in the Android view, open app > kotlin+java > com.example.app > screens > MainScreen.kt

   Create a map view model that extends ViewModel.

   MainScreen.kt

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
   class SceneViewModel : ViewModel() {
   
   }
   
   

   Expand

2. In the MainScreen composable, delete the entire function body. Leave just the function declaration as shown below. Then delete the top-level code for creating a map that is part of the Display a map tutorial. In this tutorial, you will create the map within the view model.

   MainScreen.kt

   Expand

   Use dark colors for code blocksCopy

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
   @Composable
   fun MainScreen() {
   
   }
   MainScreen.kt

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   fun createMap(): ArcGISMap {
   
       return ArcGISMap(BasemapStyle.ArcGISTopographic).apply {
   
           initialViewpoint = Viewpoint(
               latitude = 34.0270,
               longitude = -118.8050,
   
               scale = 72000.0
   
           )
   
       }
   
   }

3. In the view model, create an ArcGISScene from a PortalItem. Then create a SceneViewProxy.

   MainScreen.kt

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       private val portal = Portal(
           url = "https://www.arcgis.com",
           connection = Portal.Connection.Anonymous
       )
   
       private val portalItem = PortalItem(
           portal = portal,
           itemId = "7558ee942b2547019f66885c44d4f0b1"
       )
   
       var scene = ArcGISScene(portalItem)
   
       val sceneViewProxy = SceneViewProxy()
   

   Expand

Create a viewshed analysis

Visual analyses are used to help you make sense of complex 3D data contained by a scene. Use a LocationViewshed to perform and display a viewshed analysis using a 3D point to define the observer's location.

1. In the view model, create an AnalysisOverlay named analysisOverlay to contain and display the viewshed analyses.

   More info

   An analysis overlay is a container for Analysis objects. It is used with a scene view to display visual analyses on a scene. You can add more than one analysis overlay to a scene view. Analysis overlays are displayed on top of all other layers and graphics overlays.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       // The analysis overlay to be added to the scene.
       val analysisOverlay = AnalysisOverlay()
   

   Expand

2. Create a LocationViewshed named viewshed.

   More info

   The viewshed analysis is added to a scene view using an analysis overlay. An analysis overlay is a container for analyses. It can be used to display visual analyses in a scene view. You can add more than one analysis overlay, and they are displayed on top of all other layers.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       var viewshed = LocationViewshed(
           location = Point(x = 0.0, y = 0.0),
           heading = 0.0,
           pitch = 90.0,
           horizontalAngle = 360.0,
           verticalAngle = 180.0,
           minDistance = 10.0,
           maxDistance = 12_000.0
       )
   

   Expand

3. In the init block, make the viewshed not visible upon launch and add the viewshed to the analysis overlay. Then load the scene. Since load() is a suspend function, call it from viewModelScope.launch.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       init {
           viewshed.isVisible = false
           analysisOverlay.analyses.add(viewshed)
   
           viewModelScope.launch {
               scene.load().getOrElse { logError(it) }
           }
       }
   

   Expand

4. Define a function named setViewshedLocation() that takes a Point as a parameter. This function sets the location of the viewshed and makes it visible, if it is not visible already.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       private fun setViewshedLocation(point: Point) {
           viewshed.location = point
           viewshed.isVisible = true
       }
   

   Expand

5. Define a function named hideViewshed(), which hides the viewshed without modifying or deleting it. Then create a function named setViewshedDistance() to set a new maximum distance value for the viewshed.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       fun hideViewshed() {
           viewshed.isVisible = false
       }
   
       fun setViewshedDistance(maxDistance: Double) {
           viewshed.maxDistance = maxDistance
       }
   

   Expand

Display the viewshed analysis with touch events

Touch events determine where to place the observer for the viewshed analysis. A user will long-press and drag to reveal and move the observer's location.

1. Define a function named handleLongPressEvent() to add or move the viewshed analysis when the user long-presses on the scene. To obtain the new location (Point) in the scene, call screenToLocation() on the SceneViewProxy, passing in the screen coordinate of the long-press. Then call your setViewshedLocation() with the scene point.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       fun handleOnLongPress(screenCoordinate: ScreenCoordinate) {
           viewModelScope.launch {
               val scenePoint = sceneViewProxy.screenToLocation(screenCoordinate).getOrElse { error ->
                   return@launch logError(error)
               }
               setViewshedLocation(scenePoint)
           }
       }
   

   Expand

2. Define a function to log errors.

   SceneViewModel class

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       private fun logError(error: Throwable) {
           Log.e(this.javaClass.simpleName, error.message.toString(), error.cause)
       }
   

   Expand

Add a UI to control the viewshed analysis

To control the viewshed analysis, some UI elements are required.

1. Create variables in the MainScreen composable.

   • Create sceneViewModel using viewModel().
   • Create sliderValue of type MutableFloatState. Since viewshed.maxDistance in the view model is a Double, but the value passed to Jetpack Compose Slider composable is a Float, you must convert the max distance to a Float.
   MainScreen()

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
   @Composable
   fun MainScreen() {
   
       val sceneViewModel: SceneViewModel = viewModel()
       // If viewshed.maxDistance is not null, assign it to maxDistance. Otherwise, assign default of 1000.0
       var sliderValue by remember {
           mutableFloatStateOf(sceneViewModel.viewshed.maxDistance?.toFloat() ?: 1000.0f)
       }
   
   }

2. Add a Scaffold and pass a TopAppBar. The Scaffold's content lambda contains a Column.

   MainScreen()

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
   @Composable
   fun MainScreen() {
   
       val sceneViewModel: SceneViewModel = viewModel()
       // If viewshed.maxDistance is not null, assign it to maxDistance. Otherwise, assign default of 1000.0
       var sliderValue by remember {
           mutableFloatStateOf(sceneViewModel.viewshed.maxDistance?.toFloat() ?: 1000.0f)
       }
   
       Scaffold(
           topBar = { TopAppBar(title = { Text(text = stringResource(id = R.string.app_name)) }) }
       ) { innerPadding ->
           Column(
               modifier = Modifier.padding(innerPadding),
               horizontalAlignment = Alignment.CenterHorizontally,
               verticalArrangement = Arrangement.spacedBy(12.dp)
           ) {
   
           }
       }
   
   }

3. In the Column's content lambda, add the SceneView composable. For the arcGISScene, sceneViewProxy, and analysisOverlays parameters, pass the corresponding properties from sceneViewModel. For onLongPress, pass a lambda that calls sceneViewModel.handleOnLongPress().

   MainScreen()

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
       Scaffold(
           topBar = { TopAppBar(title = { Text(text = stringResource(id = R.string.app_name)) }) }
       ) { innerPadding ->
           Column(
               modifier = Modifier.padding(innerPadding),
               horizontalAlignment = Alignment.CenterHorizontally,
               verticalArrangement = Arrangement.spacedBy(12.dp)
           ) {
   
               SceneView(
                   modifier = Modifier
                       .fillMaxSize()
                       .weight(1f),
                   arcGISScene = sceneViewModel.scene,
                   sceneViewProxy = sceneViewModel.sceneViewProxy,
                   analysisOverlays = listOf(sceneViewModel.analysisOverlay),
                   onLongPress = { longPressEvent ->
                       sceneViewModel.handleOnLongPress(longPressEvent.screenCoordinate)
                   }
               )
   
           }
       }
   

   Expand

4. Add a Text to display the current value of the slider.

5. Add a Row that will contain a Slider and a TextButton.

   The slider allows the user to adjust the maximum distance of the viewshed in the range of 0f..20999f. The value parameter is the current value of the slider, which is held in the sliderValue variable of the MainScreen composable. For the onValuechange parameters pass a lambda that saves the new value of the slider in the sliderValue variable and then calls setViewshedDistance() in the view model. Changing the maximum distance of the viewshed expands or contracts the size of the observer's field of view.

   The text button says "Clear" and calls the view model's hideViewshed() when clicked. This allows the user a fresh start to make more analyses.

   MainScreen()

   Expand

   Use dark colors for code blocks

   1
   2
   3
   4
   5
   6
   7
   8
   9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
   100
   101
   102
   103
   104
   105
   106
   107
   108
   109
   110
   111
   112
   113
   114
   115
   116
   117
   118
   119
   120
   121
   122
   123
   124
   125
   126
   127
   128
   129
   130
   131
   132
   133
   134
   135
   136
   137
   138
   139
   140
   141
   142
   143
   144
   145
   146
   147
   148
   149
   150
   151
   152
   153
   154
   155
   156
   157
   158
   159
   160
               Text(text = "Viewshed max distance: "+sliderValue.roundToInt().toString())
               Row {
                   Slider(
                       modifier = Modifier.weight(1f),
                       value = sliderValue,
                       valueRange = 0f..20999f,
                       onValueChange = {
                           sliderValue = it
                           sceneViewModel.setViewshedDistance(sliderValue.toDouble())
                       },
                   )
                   TextButton(onClick = { sceneViewModel.hideViewshed() }) {
                       Text(text = "Clear")
                   }
               }
   

   Expand

Click Run > Run > app to run the app.

You should see a scene of hotspots in the Yosemite Valley. Long-press and drag to display and move a viewshed analysis to explore the visibility of terrain from various locations.

What's next?

Learn how to use additional API features, ArcGIS location services, and ArcGIS tools in these tutorials: