Show this v.sample video to change scale , size for model 3d

https://youtu.be/Y1LqtleBezc?list=PLazvcyckcBwjSxqwlSr6c2l8FEK-vxSV8

And change image size by button on gui
https://youtu.be/2oGGZl0h8co?list=PLazvcyckcBwjSxqwlSr6c2l8FEK-vxSV8

You can be used script model change size to image

Working on Unity 5.6.x and unity 2017

Well, it seems the code I found needed some foolproofing, as I'm fool enough to fall in the only trap it had for me !

Long story short, I was only checking that I was getting a null on Vuforia's virtual preview. Wich is absolutely normal : it seems the Trackers are all null when using only a preview as there is no point trying to see real items when playing my app on a pure virtual context !

I eventually ended up with "Disable Vuforia Play" checkbox unchecked (on ARCamera -> Web Cam Behaviour) after switching through a couple versions of Unity (function that I didn't know even exist !) and realized I wasn't getting a null value when using an actual camera. Since my app is designed for Android (and getting Debug.Log outputs on Android is a mess...) and since I usually get stuff working better on Unity previews than on actual Android runtime, I figured that having null on Unity couldn't lead to better luck on Android...

Anyway, if other fools like me somehow ends up here, since I have the foolproof code, I might as well share it ;)

    private void resizeMarker(ImageTargetBehaviour imageTarget, Vector2 size)
    {
        //No point trying to rescale if it's already scaled !
        if(imageTarget.transform.localScale.x == size.x && imageTarget.transform.localScale.z == size.y)
        {
            return;
        }
        //Retreiving the track
        ObjectTracker tracker = TrackerManager.Instance.GetTracker<ObjectTracker>();
        //foolproofing !
        if (tracker == null)
        {
            Debug.LogWarning("You might be using a virtual camera (Vuforia Play). The scaling of the trackable "+imageTarget.name+" will only be virtual wich doesn't unsure your function will work in actual runtime");
        }
        else
        {
            //Retreiving all datasets
            IEnumerable<DataSet> sets = tracker.GetActiveDataSets();
            bool foundAndReplaced = false;
            //browsing through the datasets
            using (var setsEnum = sets.GetEnumerator())
            {
                while (!foundAndReplaced && setsEnum.MoveNext())
                {
                    DataSet ds = setsEnum.Current;
                    //deactivating every datasets, one at a time
                    tracker.DeactivateDataSet(ds);
                    //retreiving all trackables
                    IEnumerable<Trackable> tracks = ds.GetTrackables();
                    //browsing through trackables
                    using (var tracksEnum = tracks.GetEnumerator())
                    {
                        while (!foundAndReplaced && tracksEnum.MoveNext())
                        {
                            Trackable trackable = tracksEnum.Current;
                            //Looking for Image Targets
                            if (trackable is ImageTarget)
                            {
                                ImageTarget it = trackable as ImageTarget;
                                //Looking for MY image target that I need to update
                                if (it.ID == imageTarget.ImageTarget.ID)
                                {
                                    //Now, Vuforia knows the real size of my target
                                    it.SetSize(size);
                                    foundAndReplaced = true;
                                }
                            }
                        }
                    }
                    //Once I'm done with this dataset, I can reactivate it
                    tracker.ActivateDataSet(ds);
                }
            }
        }
        //Updates the virtual size of my imagetarget along with his child GameObjects. (Also does the scaling on Vuforia previews !)
        imageTarget.transform.localScale = new Vector3(size.x, 1, size.y);
    }

Well, seems like a new version of Vuforia (5.5.9) is out and was made compatible with the latest version of Unity : 5.3.3.
I'll try to see if eventually that can fix my problem...

(I was on Unity 5.1.1 and Vuforia 5.0.10)

I'll post an update if I can get this to work properly.