World Center Problems

May 20, 2015 - 1:37pm #1

I am developing an application which will have a very large image target (at least 2 feet tall and a foot wide) and I want to enable the tracking to work at extremely close ranges and not lose the tracker.

As such, I broke the target image down into 8 fragments and made each one an image target, arranged them in Unity so that they are all in their proper respective places, but I've noticed a slight issue:

If the first target detected isn't the correct one (top-left most?) then the 3D model appears offset.  I have determined that this is due to the WorldCenterMode setting being set to "first target."

However, my attempts at using any of the other modes have rendered the application non-operational, where it (appears) to never detect the targets at all, and certainly doesn't track them.

I made a recording, available here:

You can see that it works very well in the "first target" mode with the exception of being offset if the centered target is the wrong one, but in the other two modes it doesn't work at all.  You can hear my coworkers talking about it (our designer was showing it off to a couple of other folks just as I was setting up to record the issue).

World Center Problems

October 18, 2015 - 7:06pm #14

this could be a useful reference for discussing my problem [posted on the forum as 'Aligning AR view with actual view...']

i am trying to display a room re-design in AR view so that it aligns with the actual existing room ... so i set up a multi-target config and placed the model accordingly in unity....

but at runtime the AR display is not exactly aligned with the actual room....

so when i am near a tracked target the nearby portions of the room appear at exactly the place they are supposed to be,

however, the farther points in the AR view [e.g. the end wall of the room] appears at a shorter distance [than the actual end wall of the room]...

i have naroowed this down to an issue with the projection matrix....but need help to solve this issue...

[using ipad-mini in landscape mode]

thnx in advance...

World Center Problems

September 30, 2015 - 6:58am #13

You can just use a DefaultTrackableEventHandler, at least that's what I did, but you'll probably want to locate all the augmentations as root-level game-objects, i.e. not as children of the targets; the key is that the World Reference will be anchored to the Trackables with their relative positions.

That's how it works.


For the World Center Mode, it seems there isn't a specific piece of doc anymore just for that, but it is explained in this tutorial:

(although the video still refers to AUTO, USER, instead of CAMERA, FIRST_TARGET and SPECIFIC_TARGET).



World Center Problems

September 30, 2015 - 5:08am #12

Hi Alessandro,

I just wanted to check whether in this example you setup, did you use a different TrackableEventHandler, rather than the default ImageTrackableEventHandler?

The reason I ask is that the default one assumes objects/augmentations are children of the ImageTarget, while the scene you have a picture of shows the cube as being independent of the image target, in which case the default ImageTrackableEventHandler would not be able to show it?

I am interested in this because I am aiming to do something similar.


kind regards,


BTW Do you know where the World Center documentation is because I cannot find it?

World Center Problems

June 11, 2015 - 5:39am #11

Ah ha, gotcha.


World Center Problems

June 11, 2015 - 4:41am #10

What I mean is that the gameobject that you put independent of the image target moves with the AR Camera. So when you move your device around, your game object remains in the same 2D coordinates on the screen until the image target is no longer being tracked. I want the game object to remain in a position relative to the image target without moving when the AR camera moves.

World Center Problems

June 10, 2015 - 1:54pm #9

Mm, pronoun game.

Not sure what "the object"  or "it" is.

And going back to my original post, any setting other than first target moves neither camera nor world objects.  Your post has not clarified why that is, yes.

World Center Problems

June 10, 2015 - 12:26pm #8

I tried the demo you put up. When you leave the object in the root directory, it will always generate the object. Also, when you store it with an image target and you set world view to first target, it still moves with the camera rather than with the image target.

World Center Problems

May 22, 2015 - 6:38am #7

It was a placeholder printout, I'm getting an updated one that's got a background filled in this morning.  Still not final, but it's complete enough that I'll be able to see if that is the problem or not.

And yes, it is broken into 8 pieces :)

World Center Problems

May 22, 2015 - 5:30am #6

What I noticed in the video you posted (if I imagine breaking up the human body atlas big image into 8 pieces), is that some portion of the image (i.e. some image targets) have a lot of white areas and only some details on a corner; clearly there are some differences between a target and another, but I wonder if the differences are too little and might confuse the tracker...

an easy verification might be to replace the top-left and top-right (i.e. around the human shoulders) with a "chips" and a "stones" (while leaving the rest of the image atalas the same) and verify the different behaviour...

World Center Problems

May 22, 2015 - 5:22am #5

I wouldn't have thought any of them looked alike.

The final version of the poster should be a better target, what I'm using now was just what the designer was starting with before he added text and other graphical elements.

World Center Problems

May 22, 2015 - 1:18am #4

...Ok, I did not have any problems using the sample targets.  No matter how many of them I had visible at the start or made not-visible, the camera tracked just fine...


Thanks for confirming.

This is suggesting that the issue might be with something specific about your project setup or maybe with the targets used;

for example, are any of those targets looking similar (maybe "too similar" possibly) to one another ?

I wonder if the Tracker might get confused by detecting a target for another...

A simple exercise would be to replace the targets in your "atlas" one by one with another set of image targets (while leaving the 3D models at their current location, no change), and/or to review the image targets with a quick visual inspection and identify (potentially) 2 or 3 of them that might look very similar and then focus on those... for example, you might need to edit one or 2 of those in an Image Editor just to add some little extra details...

That's one hypothesis...



World Center Problems

May 21, 2015 - 8:44am #3

I'll take a look here shortly.

BTW, the sample targets are useless post 4.0, as they have an associated product license key, which is not supplied (or they don't have one at all, which still makes them almost useless).  Which means I have to upload those to my own database and redownload them.


Ok, I did not have any problems using the sample targets.  No matter how many of them I had visible at the start or made not-visible, the camera tracked just fine.  If you would like, I can zip up this project and send it over for examination.

World Center Problems

May 21, 2015 - 7:09am #2

Thanks for the report, and the video.

I've tried to reproduce the issue making this quick test that mimics what you're doing but on a simpler scale:

  • I have create a scene with an ARCamera and 3 Image Targets: Chips, Stones and Tarmac (you can take those from the Vuforia Image Targets sample)
  • I have arranged them on a sort of 2 x 2 grid configuration, i.e.:
    • the "chips" taget is located at (0,0,0) in the Unity scene
    • the "stones" target is located at (0,0,200), i.e. at the "north" of the "chips" target
    • the "tarmac" target is located at (200,0,0), i.e. on the right of the "chips" one
  • I have put the ARCamera at (0,400,0) in the scene, but note that this should not matter for this test (the ARCamera will anyway change its position at runtime as soon as a target is detected)
  • I have set World Center Mode to FIRST_TARGET (i.e. the default)
  • I have set Max Simultaneous Image Targets = 1 (i.e. the default)
  • I have then added a cube to the scene, at root level and located at (150, 15, 100) and with scale (200, 30, 200)

I have then printed the 3 targets on an A4 paper using the same spatial configuration (i.e. tarmac on the right of chips, and stones above chips)

Tried running and it seems to work fine, i.e. the Cube appears right at the expected location, no matter which target is detected first.

See attached screenshot that shows the Unity scene setup.

Could you make the same quick test ?



Image icon Unity-multi-target-setup.png187.72 KB
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