Unity中是否有Target.position函数？如何获取用户与AR目标相对位置

Hey there! Let's break down your questions step by step, tailored to your museum pendulum interaction project:

1. Target.position Equivalent for Vuforia 2D Markers #

There’s no direct Target.position function, but Vuforia’s 2D Image Targets (which you’re using) expose their real-world position via the Transform component of the tracked object. Once your marker is recognized, you can grab its position with:

Vector3 targetPos = yourImageTarget.transform.position;

This gives you the 3D coordinates of the pendulum’s marker at any frame—exactly what you need for tracking its movement.

2. Calculating User's Relative Position to the AR Target #

Since your visitors always face the exhibit (no need to handle rear positions), this simplifies things a lot:

• Distance to the target: Use Vector3.Distance() to get the straight-line distance between the user’s camera (their viewpoint) and the pendulum marker:

  float distanceToPendulum = Vector3.Distance(Camera.main.transform.position, targetPos);
  

• Relative position vector: Subtract the target’s position from the camera’s position to get a vector pointing from the pendulum to the user. Since you don’t care about height differences (visitors are standing in front), you can zero out the Y component to focus on horizontal positioning:

  Vector3 userRelativeToPendulum = Camera.main.transform.position - targetPos;
  userRelativeToPendulum.y = 0; // Ignore vertical offset
  

  This vector tells you exactly where the user is positioned relative to the swinging pendulum (e.g., left/right, forward/backward in the horizontal plane).

3. Implementing Velocity Vector Display for Your Moving Pendulum #

Since the pendulum is in motion, you’ll need to track frame-to-frame position changes to calculate velocity. Here’s a practical script example you can adapt directly:

using UnityEngine;
using Vuforia;

public class PendulumVelocityTracker : MonoBehaviour
{
    [Header("AR Setup")]
    public TrackableBehaviour pendulumMarker; // Assign your 2D Image Target here
    public LineRenderer velocityVectorRenderer; // For drawing the visible velocity line

    private Vector3 lastFramePosition;
    private Vector3 currentVelocity;

    void Start()
    {
        if (pendulumMarker != null)
        {
            // Subscribe to marker tracking events
            pendulumMarker.OnTrackableStateChanged += OnMarkerTrackingChanged;
            lastFramePosition = pendulumMarker.transform.position;
            velocityVectorRenderer.enabled = false;
        }
    }

    void Update()
    {
        if (pendulumMarker.CurrentStatus == TrackableBehaviour.Status.TRACKED)
        {
            Vector3 currentPos = pendulumMarker.transform.position;
            // Calculate velocity: displacement divided by time since last frame
            currentVelocity = (currentPos - lastFramePosition) / Time.deltaTime;
            
            // Smooth velocity to reduce Vuforia tracking jitter
            currentVelocity = Vector3.Lerp(currentVelocity, currentVelocity * 0.9f, Time.deltaTime * 5f);

            // Draw the velocity vector (adjust the multiplier for visibility)
            velocityVectorRenderer.SetPosition(0, currentPos);
            velocityVectorRenderer.SetPosition(1, currentPos + currentVelocity * 0.3f);

            // Update last position for next frame calculation
            lastFramePosition = currentPos;

            // Optional: Log distance for debugging
            float userDistance = Vector3.Distance(Camera.main.transform.position, currentPos);
            Debug.Log($"Visitor to pendulum distance: {userDistance:F2}m");
        }
    }

    void OnMarkerTrackingChanged(TrackableBehaviour.Status previousStatus, TrackableBehaviour.Status newStatus)
    {
        // Enable/disable the velocity line based on tracking state
        velocityVectorRenderer.enabled = newStatus == TrackableBehaviour.Status.TRACKED;
        if (newStatus == TrackableBehaviour.Status.TRACKED)
        {
            lastFramePosition = pendulumMarker.transform.position;
        }
    }
}

Key Notes for This Script: #

• Jitter Reduction: The Vector3.Lerp line smooths out small tracking jumps from Vuforia, which is crucial for a clean, professional-looking velocity display.
• Visibility: Adjust the 0.3f multiplier to make the velocity vector longer or shorter based on the real size of your pendulum.
• Tracking Reliability: Place your 2D marker on a high-contrast, rigid part of the pendulum (like the bob) so Vuforia doesn’t lose track during fast swings.

4. Quick Tips for Your Museum Setup #

• You mentioned the "3D AR Markers with Project Tango" forum—while Tango tech is now integrated into Google AR Core, your choice of Vuforia 2D markers is perfect here. 2D markers are far more stable for fast-moving objects like pendulums compared to 3D object scanning (which you had issues with).
• Test marker size: A larger marker (6-8 inches across) will be easier for Vuforia to track as the pendulum swings through its range.
• Calibrate your AR camera in Unity to ensure the velocity vector aligns perfectly with the real pendulum’s movement—this will make the interaction feel seamless for visitors.

内容的提问来源于stack exchange，提问作者arantxa