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Offsets on Hologram

March 14, 2019 - 8:14am #1

Hello



I'm currently trying to developt a small app using Unity 2017.4.0f1 and Vuforia 7.0.47

This app is suppose to scan a image target, and display an hologram on a real model.

My current image target is 6cm by 5cm. In Unity and Vuforia's Database, I've set the height at 0,05.

On my app, the Hololens is able to recognize the Image target and display the hologram. However, I always have an offset between the hologram and the real model. The hologram will always be displayed in front of my image target in the real world whereas in Unity, I've set it behind it.



Do we have a way to perfectly synchronize the position of the hologram depending of the image target ?

 

Thank you for your answer.

Offsets on Hologram

March 18, 2019 - 5:04am #6

Hello

 

Thanks both of you for your answers.

I understand a little bit more, and try to work on it for my part.

Offsets on Hologram

March 18, 2019 - 3:47am #5

Hello,

From our experience, there are several factors that can cause an augmentation to be offset, including:

  • HoloLens user calibration. MS recommends that each user perform the HoloLens calibration steps before using the device. This is obviously tedious, but when sharing HL devices within a team we've chased a similar performance 'ghosts' that were resolved when a user calibrated the device for themselves.
  • The size of your printed targets. For optical see-through devices (such as HoloLens), the printed target must match the dataset's target size exactly, as uploaded to the Target Manager. Recall that the Target Manager works exclusively in the units of meters.
  • HoloLens device calibration. All HL devices have some level of factory calibration done before shipment, and we've had to have devices re-calibrated by MS. Although this does not seem to be the source of your issue, it is something to be aware of with HL devices that the factory calibration can be compromised.

You may also want to examine the HL mesh in that area. This can be done by orienting the retical towards the area in question and "air-tapping" while in the HL shell (the home screen without the start menu - no apps running). Perhaps this will reveal some errors in the HL spacial map that are affecting their position estimations.

Thanks,

Vuforia Engine Support

Offsets on Hologram

March 15, 2019 - 3:52am #4

In Unity the x,y,z corresponds to right, up forward. In addition to that, there are world coordinates and local coordinates. If your object is a child of the ImageTarget, (0,0,0) will be at the origin of the ImageTarget and represent local coordinates, on the other hand if your object is not a child of anything in the hierarchy, (0,0,0) will be the origin of the world coordinate system which corresponds to the initial position of the Hololens when you start your app.

I think I misinterpreted, what you meant with "behind", think of your ImageTarget lieing flat on a surface and looking at it at an angle, so yes the y axis = normal of the marker would determine if and object is in front or behind your target. Using a higher rated image with a lot of features increases the detection and tracking stability.

Furthermore, a slight deviation of the position is to be expected since the algorithm for detection/tracking has a certain margin of error.

Offsets on Hologram

March 15, 2019 - 1:31am #3

Hello

So you mean that I have to correct the position of my object depending the Z axis ?

Here my image target plan is using X and Z axis. I thought that for setting the object behind the imageTarget, I should use the Y axis. Isn't that correct ?

I don't manage to put where I want the hologram, even if I'm setting the position of my object at (0,0,0), I'm expecting to find the object half on the image target, but it isn't. I'm feeling that it's taking the position of my head instead of the position of the image target.

 

EDIT : 

In the end, I've just used a better image target (5 star rating), and I worked on the offset directly in Unity, trying to match the hologram with the real world model.

I just wanted to know if there is a faster solution than this one ?

Offsets on Hologram

March 14, 2019 - 8:56am #2

Are you sure you placed your object correctly in Unity? The Camera will look along the z axis so if object.position.z > target.position.z, the object will be behind the target, otherwise it will be in front of the target

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