Working with large distances (Floating Origin)

The Floating Origin System is a solution designed to manage 3D world coordinates in Unity3D. It operates on the idea of retaining the real-world coordinates of objects while the origin within the computer-generated world adjusts. The Floating Origin System achieves this through the integral use of the following components:

Overview of the Floating Origin System

Before the deep-dive into the components of the Floating Origin system, a basic understanding of the concepts in this system is required:

Real world coordinates and Unity positions

In Unity, the transform component is responsible for tracking the position relative to Unity's (0,0,0) origin point, when working with large worlds -such as our real-world- this system no longer works due to floating point precision errors. To solve this, a second mechanic for tracking positions is introduced using real world coordinates in the WGS84 lat/long ECEF coordinate system.

As the distances expressed by real world coordinates are greater than Unity's floating point based transforms, it is needed to track the real world coordinate of the (0,0,0) origin -called the Floating Origin- and the coordinates of real world objects.

When the camera moves thus far away from the Floating Origin that floating point issues may occur, the origin will change its real-world coordinate to be nearer to the camera's real-world coordinate and shift the Unity position of all real-world objects to match the new real-world coordinate of Unity's (0,0,0) origin.

(Floating) Origin

The Origin represents the real world coordinates of Unity's (0,0,0) origin and is responsible for tracking the distance of the Camera from Unity's (0,0,0) origin. If the Camera moves too far away, rendering and calculation anomalies can happen due to floating point precision issues and all real world objects -including the origin's own real-world coordinates- need to be shifted so that all elements are back into a safe distance in Unity's coordinate system.

Shifting

Shifting is the term for when real world objects need to have their Unity position adjusted to get closer to the Floating Origin. Because the origin's Unity position never changes -it is always at 0,0,0- but its real-world coordinate can change, we need to respond to that by moving real-world objects' Unity position. As soon as this happened, all Game Objects should be within a safe distance from 0,0,0 again.

Real-world objects

Real-world objects -sometimes referred to as spatial objects- are game objects whose location is tied to the real-world and have a location in the real world. An example may be a windmill, where a UI element is an example of something that is not.

Real-world objects have a World Transform component that tracks the real-world position and orientation of the object and when a shift is emitted, they will reposition themselves or its parts.

World Transform

The World Transform tracks the real-world position and orientation for a real-world object. The World Transform also reacts to the Origin calling for a shift, but delegates the actual work to a World Transform Shifter component. This allows for objects to respond to shifts differently.

World Transform Shifter

The World Transform Shifter is the component that handles the shifting of a Game Object. Usually you do not need to provide a specific World Transform Shifter with a World Transform, in that case the default GameObjectWorldTransformShifter is used.

Origin

In the Floating Origin System, the Origin is an important concept referring to the focal point within the Unity game world. It is crucial for large scale projects where precision becomes a challenge.

The Origin is typically associated with its own separate GameObject. This GameObject serves as an indicator or marker of the origin point, and doesn't have any visual representation in the game environment. Its primary role is to maintain the game world's central point and handle shifts in that point to ensure accuracy and consistency in objects' locations in the world.

To use the Origin, create an empty GameObject in your scene. This empty GameObject often doesn't need any other components besides Origin. Then, attach the Origin script to this GameObject. Now, the Origin GameObject will continually monitor its distance from the camera (or a specified mainShifter object) while playing.

Performance Optimizations in Origin

Understanding and managing performance is key in any system, and the Floating Origin System includes several performance optimizations to ensure efficient operation.

Using sqrMagnitude Instead of Magnitude

The process of calculating distance often involves the operation of square roots, which introduce computational complexity. In the Floating Origin System, we use Unity's built-in sqrMagnitude method instead of magnitude for distance calculations.

The sqrMagnitude method calculates the square of the magnitude of a distance vector, which omits the need for a square root operation. Since the Origin uses a squared threshold for determining shifting necessity, this optimization aligns perfectly. Simply put, both the mainShifter's distance and the threshold are squared values, so no square root operation is needed, resulting in improved performance without comprising correct operation.

Using a Coroutine to Wait Until the End of Frame

The Floating Origin System uses Unity's Coroutine feature to postpone the shifting evaluation to the end of each frame. The shifting operation checks at the end of the frame if it needs to reposition the Origin based on the final position of the mainShifter.

This optimization minimizes unnecessary Origin shifting, as multiple changes to the mainShifter position within a single frame will only trigger the shifting operation once at the end of the frame. This approach effectively reduces computational load by minimizing the frequency of costly shifting operations.

The Origin triggers the shifts

The Origin in the Floating Origin System demonstrates an example of encapsulation, a fundamental principle of object-oriented programming. Instead of distributing responsibilities across multiple components (like making the camera responsible for calculating distances and triggering shifts), the Floating Origin System centralizes these responsibilities within the Origin.

Encapsulating Responsibilities

The Origin is responsible for continually monitoring its distance from the camera (or another defined mainShifter object). Using a pre-determined threshold, the Origin decides when the shift operation needs to occur. Once that threshold is surpassed, the Origin triggers a shift operation to reestablish itself closer to the camera or mainShifter. This design decision encapsulates the behavior within the Origin, making it a standalone component that can independently determine and respond to shifts.

Performance and Design Improvements

The encapsulation model presents several advantages:

• Performance: By monitoring the mainShifter's distance at the end of each frame and shifting only when necessary, the Origin can optimize performance and reduce unnecessary shifts, irrespective of how many changes occur to the mainShifter during the frame.

• Design Simplicity: Having the Origin act as the central point of control simplifies task delegation amongst components and makes the overall system easier to understand.

• Encapsulation: By keeping related functions within the Origin, the design favors encapsulation, ensuring a clean system where components' responsibilities are clearly defined and do not blend.

WorldTransform

An analogy: transforms and rigidbodies

To illustrate how the WorldTransform and their Shifters work, you can compare them to the way Transform and RigidBodies work in Unity. The Transform holds the position, rotation and scale and can be manipulated; but the actual physics interaction -movement forced by external factors- is accomplished through a RigidBody component, or even a CharacterController.

In Unity, you have one transform and one type of RigidBody/Character Controller; and with the WorldTransform this works similarly: the WorldTransform works like a Transform and records the position of the real-world object, where a WorldTransformShifter functions like a RigidBody and exerts force on the WorldTransform when a Shift happens.

The WorldTransform is effectively the real-world equivalent of an object's location within the Unity game world. When the Origin shifts, the WorldTransform is adjusted correspondingly. Meanwhile, Unity's native Transform class remains untouched. This results in two interconnected, but separate, coordinate systems.

Not all objects will need to handle a shift in the same way. The default is to shift the GameObject itself, but some objects are containers whose children need to shift and not themselves -example: tile handlers- or where transformation matrices are used instead of transform components -example: instanced objects-. By delegating this responsibility to a World Transform Shifter all real-world objects will track their coordinates in the same way but have different ways to react to shift events.

WorldTransformShifter

The WorldTransformShifter is meant to manage the effects of moving the Origin on GameObjects. Custom behaviors for different types of GameObjects when the Origin shifts can be defined by implementing the method ShiftTo in derived classes of WorldTransformShifter.

When it is not the GameObject itself whose position needs to change but a child or something not directly linked to the transform position, then you need to use one of the other strategies. See below for more information.

Tip

The WorldTransform and its Shifters is an implementation of the Strategy design pattern.

Specialized Shifters

Specialized Shifters are used to manage Origin shifts for unique types of GameObjects not part of the Unity base package. These could be packages like Netherlands3D 3DTiles that have their unique behaviors. An example of this is ThreeDTilesWorldTransformShifter. This sub-class handles shifts for child GameObjects associated with the Content component. When an Origin shift happens, it iterates over all Content components and adjusts the positions of all their children.

Usage

To use the Floating Origin System within your Unity projects:

1. Attach the Origin component to a GameObject that will act as the world origin.
2. For objects that should maintain real-world positions, attach the WorldTransform component.
3. For specialized objects, for example, objects from the Netherlands3D 3DTiles package, attach a specialized WorldTransformShifter, like ThreeDTilesWorldTransformShifter.