Move Camera Over Terrain Using Touch Input in Unity 3D

Below should be what you need. Note that it's tricky to get a 1 to 1 correspondence between finger/cursor and the terrain when using a perspective camera. If you change your camera to orthographic, the script below should give you a perfect map between finger/cursor position and map movement. With perspective you'll notice a slight offset.

You could also do this with ray tracing but I've found that route to be sloppy and not as intuitive.

Camera settings for testing (values are pulled from the inspector so apply them there):

1. Position: 0,20,0
2. Orientation: 90,0,0
3. Projection: Perspective/Orthographic

---

using UnityEngine;
using System.Collections;



public class ViewDrag : MonoBehaviour {
    Vector3 hit_position = Vector3.zero;
    Vector3 current_position = Vector3.zero;
    Vector3 camera_position = Vector3.zero;
    float z = 0.0f;
    
    // Use this for initialization
    void Start () {
        
    }
    
    void Update(){
        if(Input.GetMouseButtonDown(0)){
            hit_position = Input.mousePosition;
            camera_position = transform.position;
            
        }
        if(Input.GetMouseButton(0)){
            current_position = Input.mousePosition;
            LeftMouseDrag();        
        }
    }
    
    void LeftMouseDrag(){
        // From the Unity3D docs: "The z position is in world units from the camera."  In my case I'm using the y-axis as height
        // with my camera facing back down the y-axis.  You can ignore this when the camera is orthograhic.
        current_position.z = hit_position.z = camera_position.y;
        
        // Get direction of movement.  (Note: Don't normalize, the magnitude of change is going to be Vector3.Distance(current_position-hit_position)
        // anyways.  
        Vector3 direction = Camera.main.ScreenToWorldPoint(current_position) - Camera.main.ScreenToWorldPoint(hit_position);
        
        // Invert direction to that terrain appears to move with the mouse.
        direction = direction * -1;
        
        Vector3 position = camera_position + direction;
        
        transform.position = position;
    }
}

I've come up with this script (I have appended it to the camera):

private Vector2 worldStartPoint;

void Update () {

    // only work with one touch
    if (Input.touchCount == 1) {
        Touch currentTouch = Input.GetTouch(0);

        if (currentTouch.phase == TouchPhase.Began) {
            this.worldStartPoint = this.getWorldPoint(currentTouch.position);
        }

        if (currentTouch.phase == TouchPhase.Moved) {
            Vector2 worldDelta = this.getWorldPoint(currentTouch.position) - this.worldStartPoint;

            Camera.main.transform.Translate(
                -worldDelta.x,
                -worldDelta.y,
                0
            );
        }
    }
}

// convert screen point to world point
private Vector2 getWorldPoint (Vector2 screenPoint) {
    RaycastHit hit;
    Physics.Raycast(Camera.main.ScreenPointToRay(screenPoint), out hit);
    return hit.point;
}