Simplifying id auto assignment by letting the user select between 0 and 1-based labels.

com.unity.perception/Editor/GroundTruth/LabelingConfigurationEditor.cs

             if (!autoAssign)
                 return;
 
-            var newFirstElement = list.serializedProperty.GetArrayElementAtIndex(0);
-            if (newIndex == 0 && list.serializedProperty.arraySize > 1)
-            {
-                var oldFirstId = list.serializedProperty.GetArrayElementAtIndex(1).FindPropertyRelative(nameof(LabelEntry.id)).intValue;
-                newFirstElement.FindPropertyRelative(nameof(LabelEntry.id)).intValue = oldFirstId;
-            }
-            if (oldIndex == 0)
-            {
-                var oldFirstId = list.serializedProperty.GetArrayElementAtIndex(newIndex).FindPropertyRelative(nameof(LabelEntry.id)).intValue;
-                newFirstElement.FindPropertyRelative(nameof(LabelEntry.id)).intValue = oldFirstId;
-            }
             AutoAssignIds();
         }
 
             using (var change = new EditorGUI.ChangeCheckScope())
             {
                 var contentRect = new Rect(rect.position, new Vector2(rect.width, EditorGUIUtility.singleLineHeight));
-                using (new EditorGUI.DisabledScope(autoAssign && index != 0))
+                using (new EditorGUI.DisabledScope(autoAssign))
                 {
                     var newLabel = EditorGUI.IntField(contentRect, nameof(LabelEntry.id), idProperty.intValue);
                     if (change.changed)
         public override void OnInspectorGUI()
         {
             serializedObject.Update();
+            var autoAssignIdsProperty = serializedObject.FindProperty(nameof(LabelingConfiguration.AutoAssignIds));
-                var autoAssignIdsProperty = serializedObject.FindProperty(nameof(LabelingConfiguration.AutoAssignIds));
+                    AutoAssignIds();
+            }
+
+            if (autoAssignIdsProperty.boolValue)
+            {
+                using (var change = new EditorGUI.ChangeCheckScope())
-                    var ok = EditorUtility.DisplayDialog("Enable auto-assigned labels", "Existing label ids will be overwritten. Enable label auto-assignment?", "Yes", "Cancel");
-                    if (ok)
-                    {
+                    var startingLabelIdProperty = serializedObject.FindProperty(nameof(LabelingConfiguration.StartingLabelId));
+                    EditorGUILayout.PropertyField(startingLabelIdProperty);
+                    if (change.changed)
-                    }
-                    else
-                        autoAssignIdsProperty.boolValue = false;
                 }
             }
 
             if (size == 0)
                 return;
 
-            var nextId = serializedProperty.GetArrayElementAtIndex(0).FindPropertyRelative(nameof(LabelEntry.id)).intValue + 1;
-            for (int i = 1; i < size; i++)
+            var startingLabelId  = (StartingLabelId)serializedObject.FindProperty(nameof(LabelingConfiguration.StartingLabelId)).enumValueIndex;
+
+            var nextId = startingLabelId == StartingLabelId.One ? 1 : 0;
+            for (int i = 0; i < size; i++)
             {
                 serializedProperty.GetArrayElementAtIndex(i).FindPropertyRelative(nameof(LabelEntry.id)).intValue = nextId;
                 nextId++;

com.unity.perception/Runtime/GroundTruth/Labeling/LabelingConfiguration.cs

     public class LabelingConfiguration : ScriptableObject
     {
         /// <summary>
-        /// Whether the inspector will auto-assign ids based on the id of the first element
+        /// Whether the inspector will auto-assign ids based on the id of the first element.
+
+        /// <summary>
+        /// Whether the inspector will start label ids at zero or one when <see cref="AutoAssignIds"/> is enabled.
+        /// </summary>
+        public StartingLabelId StartingLabelId = StartingLabelId.One;
 
         /// <summary>
         /// A sequence of <see cref="LabelEntry"/> which defines the labels relevant for this configuration and their values.

com.unity.perception/Runtime/GroundTruth/Labeling/StartingLabelId.cs

+using System;
+
+namespace UnityEngine.Perception.GroundTruth
+{
+    /// <summary>
+    /// Selector for whether label ids should start at zero or one. <seealso cref="LabelingConfiguration.StartingLabelId"/>.
+    /// </summary>
+    public enum StartingLabelId
+    {
+        /// <summary>
+        /// Start label id assignment at 0
+        /// </summary>
+        Zero,
+        /// <summary>
+        /// Start label id assignment at 1
+        /// </summary>
+        One
+    }
+}

com.unity.perception/Runtime/GroundTruth/Labeling/StartingLabelId.cs.meta

+fileFormatVersion: 2
+guid: 2f8f1d8ca6304fab94bf1c45c9ad0873
+timeCreated: 1589210485