Camera and Navigation are split into 2 properties and 2 classes

Camera holds the viewer position/dir/up.
It is automatically created with each viewport.

Navigation reacts to user input, changing camera.
It may be, but doesn't have to be, assigned to a viewport.
It's more-or-less a normal TCastleUserInterface descendant.

src/3d/castletransform.pas

@@ -1009,7 +1009,7 @@   TCastleTransform = class(TCastleComponent)
     { Main camera observing this 3D object changed.
       This is usually called by our container (like TCastleSceneManager)
       to notify that camera changed. }
-    procedure CameraChanged(ACamera: TCamera); virtual;
+    procedure CameraChanged(const ACamera: TCastleCamera); virtual;
 
     { Mouse cursor over this object. }
     property Cursor: TMouseCursor read FCursor write SetCursor default mcDefault;
@@ -1864,7 +1864,7 @@   TSceneManagerWorld = class(TCastleTransform)
     property CameraKnown: boolean read FCameraKnown;
     { @groupEnd }
 
-    procedure CameraChanged(ACamera: TCamera); override;
+    procedure CameraChanged(const ACamera: TCastleCamera); override;
 
     { Yoo can temporarily disable physics (no transformations will be updated
       by the physics engine) by setting this property to @false. }
@@ -2605,7 +2605,7 @@ procedure TCastleTransform.VisibleChangeNotification(const Changes: TVisibleChan
     List[I].VisibleChangeNotification(Changes);
 end;
 
-procedure TCastleTransform.CameraChanged(ACamera: TCamera);
+procedure TCastleTransform.CameraChanged(const ACamera: TCastleCamera);
 var
   I: Integer;
 begin
@@ -3393,7 +3393,7 @@ function TSceneManagerWorld.WorldPointCollision2D(const Point: TVector2): boolea
   Result := PointCollision2D(Point, nil);
 end;
 
-procedure TSceneManagerWorld.CameraChanged(ACamera: TCamera);
+procedure TSceneManagerWorld.CameraChanged(const ACamera: TCastleCamera);
 begin
   ACamera.GetView(FCameraPosition, FCameraDirection, FCameraUp);
   FCameraKnown := true;

src/3d/castletransform_renderparams.inc

@@ -90,7 +90,7 @@
 
     This is interesting to you only if you write custom rendering code.
 
-    In normal applications, you shoud only get/set camera using TCamera
+    In normal applications, you shoud only get/set camera using TCastleCamera
     descendants, through TCastleAbstractViewport.Camera and related properties.
     Do not use the TRenderingCamera class in normal applications. }
   TRenderingCamera = class
@@ -147,11 +147,11 @@
     function RotationMatrix3: TMatrix3;
     function RotationInverseMatrix3: TMatrix3;
 
-    { Set all properties (except Target) from TCamera instance in ACamera.
+    { Set all properties (except Target) from TCastleCamera instance in ACamera.
       See @link(FromMatrix) for comments about @link(Target) property.
       The IgnoredViewpoint parameter is only for backward compatibility,
       it is ignored. }
-    procedure FromCameraObject(const ACamera: TCamera;
+    procedure FromCameraObject(const ACamera: TCastleCamera;
       const IgnoredViewpoint: TObject = nil);
 
     { Set all properties (except Target) from explict matrices.
@@ -290,7 +290,7 @@ begin
   Move(RotationInverseMatrix.Data[2], Result.Data[2], SizeOf(Single) * 3);
 end;
 
-procedure TRenderingCamera.FromCameraObject(const ACamera: TCamera;
+procedure TRenderingCamera.FromCameraObject(const ACamera: TCastleCamera;
   const IgnoredViewpoint: TObject = nil);
 begin
   Matrix := ACamera.Matrix;

src/game/castle2dscenemanager.pas

@@ -83,7 +83,7 @@   TCastle2DSceneManager = class(TCastleSceneManager)
       DefaultCameraZ = DefaultProjectionSpan / 2;
 
     constructor Create(AOwner: TComponent); override;
-    procedure AssignDefaultCamera; override;
+    procedure AssignDefaultNavigation; override;
 
     property CurrentProjectionWidth: Single read FCurrentProjectionWidth;
     property CurrentProjectionHeight: Single read FCurrentProjectionHeight;
@@ -221,24 +221,24 @@ constructor TCastle2DSceneManager.Create(AOwner: TComponent);
   FProjectionWidth := 0;
 
   { Make camera already existing, so WalkCamera returns it,
-    instead of using AssignDefaultCamera and then switching to ntWalk. }
-  AssignDefaultCamera;
+    instead of using AssignDefaultNavigation and then switching to ntWalk. }
+  AssignDefaultNavigation;
 end;
 
-procedure TCastle2DSceneManager.AssignDefaultCamera;
+procedure TCastle2DSceneManager.AssignDefaultNavigation;
 begin
   { Set Camera explicitly, otherwise SetNavigationType below could call
-    ExamineCamera / WalkCamera that call AssignDefaultCamera when Camera = nil,
-    and we would have infinite AssignDefaultCamera calls loop. }
-  Camera := InternalWalkCamera;
+    ExamineCamera / WalkCamera that call AssignDefaultNavigation when Camera = nil,
+    and we would have infinite AssignDefaultNavigation calls loop. }
+  Navigation := InternalWalkNavigation;
 
   NavigationType := ntNone;
-  Camera.SetInitialView(
+  Navigation.SetInitialView(
     { pos } Vector3(0, 0, DefaultCameraZ),
     { dir } Vector3(0, 0, -1),
     { up } Vector3(0, 1, 0), false);
-  Camera.GoToInitial;
-  Camera.Radius := 0.01; { will not be used for anything, but set to something sensible just in case }
+  Navigation.GoToInitial;
+  Navigation.Radius := 0.01; { will not be used for anything, but set to something sensible just in case }
 end;
 
 function TCastle2DSceneManager.PositionTo2DWorld(const Position: TVector2;
@@ -262,8 +262,8 @@ function TCastle2DSceneManager.PositionTo2DWorld(const Position: TVector2;
     raise Exception.Create('TCastle2DSceneManager.PositionTo2DWorld assumes an orthographic projection, like the one set by TCastle2DSceneManager.CalculateProjection');
   ProjRect := Proj.Dimensions;
 
-  if Camera <> nil then
-    ProjRect := ProjRect.Translate(Camera.Position.XY);
+  if Navigation <> nil then
+    ProjRect := ProjRect.Translate(Navigation.Position.XY);
 
   Result := Vector2(
     MapRange(P.X, 0, EffectiveWidth , ProjRect.Left  , ProjRect.Right),
@@ -285,7 +285,7 @@ function TCastle2DSceneManager.PositionTo2DWorld(const Position: TVector2;
     P := Position * UIScale + RenderRect.LeftBottom
   else
     P := Position;
-  RequiredCamera.CustomRay(RenderRect, P, Projection, RayOrigin, RayDirection);
+  RequiredNavigation.CustomRay(RenderRect, P, Projection, RayOrigin, RayDirection);
   Result := RayOrigin.XY;
 end; }
 
@@ -300,7 +300,7 @@ function TCastle2DSceneManager.PositionTo2DWorld(const Position: TVector2;
   ScreenToWorldMatrix: TMatrix4;
   P: TVector2;
 begin
-  WorldToScreenMatrix := RequiredCamera.ProjectionMatrix * RequiredCamera.Matrix;
+  WorldToScreenMatrix := RequiredNavigation.ProjectionMatrix * RequiredNavigation.Matrix;
   if not WorldToScreenMatrix.TryInverse(ScreenToWorldMatrix) then
     raise Exception.Create('Cannot invert projection * camera matrix. Possibly one of them was not initialized, or camera contains scale to zero.');
 

src/game/castlelevels.pas

@@ -841,7 +841,7 @@ procedure TGameSceneManager.LoadLevelCore(const AInfo: TLevelInfo);
       WalkCamera.MoveVerticalSpeed := 20;
     end;
 
-    Camera := WalkCamera;
+    Navigation := WalkCamera;
 
     WalkCamera.Init(InitialPosition, InitialDirection,
       InitialUp, GravityUp, PreferredHeight, CameraRadius);
@@ -875,7 +875,7 @@ procedure TGameSceneManager.LoadLevelCore(const AInfo: TLevelInfo);
       Otherwise, it would be updated by MainScene loading binding new
       NavigationInfo (with it's speed) and Viewpoint.
       We prefer to do it ourselves in InitializeCamera. }
-    Camera := nil;
+    Navigation := nil;
 
     MainScene := TCastleScene.Create(Self);
     Inc(MainScene.InternalDirty);