Unity AR demo using ViSP

Table of contents :

1. Using ViSP Unity wrapper in Unity engine
   
2. Unity demonstrations using ViSP
   2.1. AprilTag Augmented Reality demo
   2.2. Generic Model-based Tracking demo
   
3. Tips & Tricks
   3.1. Unity crashes on MacOS
   3.2. DllNotFoundException: ViSPUnity
   

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1. Using ViSP Unity wrapper in Unity engine

This project contains in unityProject folder 2 demos that illustrate ViSP Unity wrapper usage. From here we suppose that you followed the previous tutorial that shows how to build ViSPUnity plugin that was installed in $VISP_WS/visp_unity/unityProject/Assets/ folder if you are under Linux/MacOS or in %VISP_WS%\visp_unity\unityProject\Assets\ folder if you are under Windows.

• Start Unity engine and open $VISP_WS/unityProject
• The generated ViSPUnity plugin should be visible in the Assets folder

• 36h11 AprilTag can be downloaded from here.
• In Assets > Scenes window you should see 2 scenes corresponding to AprilTag Augmented Reality demo and Generic Model-Based Tracking demo respectively

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2. Unity demonstrations using ViSP

2.1. AprilTag Augmented Reality demo

For the first project, go to the folder Assets/Scenes and open scene_ar by double click.

• You should have a similar Unity window opened, as shown below:

• Click on the Plane GameObject in hierarchy and in the inspector window modify some demo settings:
  • The Tag_size value according to you printed tag size. This value corresponds to the dimension of the black square in meters.
  • Optionally you can also modify the values of your camera parameters obtained after camera calibration.
  • If you have more than one camera attached to your computer, use Camera_id to select the camera to use. In the Console panel there are some logs that may help to identify each camera id.
  • Note also the Debug_display option that is disabled by default. If enabled it will open a windows in which the current image is displayed with computer vision results that may be useful to understand the low level processing achieved with ViSP.

• Notice that the gameObject Cube is a child of gameObject Cube_pivot. This is done to make sure that the cube rotates around the center of one of the faces.

• The current implementation takes care of position, scaling and rotation of the cube. A small YouTube Video demonstration is also available here.

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2.2. Generic Model-based Tracking demo

For the second project, go to the folder Assets/Scenes and open scene_mbt by double click.

• You should have a similar Unity window opened, as shown below:

• For this demonstration, we are using a 7cm x 7cm x 7cm cube made from cardboard. A 36h11 AprilTag (4.8cm x 4.8cm) is pasted on one of its faces for tracker initialisation. We strongly recommend to put texture on the other cube faces so that the tracker benefits from keypoint features. Here is a picture for reference:

• Click on the Plane GameObject in hierarchy and in the inspector window modify some demo settings:
  • The Tag_size value according to you printed tag size glued on one cube face. This value corresponds to the dimension of the black square in meters.
  • The Cube_size value according to your cube.
  • Optionally you can also modify the values of your camera parameters obtained after camera calibration.
  • If you have more than one camera attached to your computer, use Camera_id to select the camera to use. In the Console panel there are some logs that may help to identify each camera id.
  • Note also the Debug_display option that is disabled by default. If enabled it will open a windows in which the current image is displayed with computer vision results that may be useful to understand the low level processing achieved with ViSP.

• Now, click play button to start. A small YouTube Video demonstration is also available here.

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3. Tips & Tricks

3.1. Unity crashes on MacOS

This issue comes from MacOS camera authorization requested before usage in Unity.

The work around is to quit Unity Hub and launch it from a terminal:

$ /Applications/Unity\ Hub.app/Contents/MacOS/Unity\ Hub

If this is not enough, try to quit properly your opened applications and restart your computer.

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3.2. DllNotFoundException: ViSPUnity

• Check if in $VISP_WS/visp_unity/unityProject/Assets/ there is the ViSPUnity plugin named ViSPUnity.dll under Windows, ViSPUnity.so under Ubuntu and ViSPUnity.bundle if you are on OSX.
• If the file is missing, it means that you forget to call make install after building vispWrapper project as explained in the previous tutorial.
• If the file is present, quit Unity, start Unity and try to run again unityProject.

When you change the code in vispWrapper project and do a fresh installation using make install that copies the bundle in the unityProject/Assets folder, you should quit and restart Unity to reload the modified plugin.