Set up ArUco markers

First of all, ArUco markers needs to be printed and placed into the scene.

Here is an example scene where markers are surrounding a workspace with two screens, a control panel and a window.

Print ArUco markers from an ArUco dictionary

ArUco markers always belong to a set of markers called the ArUco marker dictionary.

Many ArUco marker dictionaries exist with properties concerning the format, the number of markers, or the difference between each marker to avoid errors in tracking.

Here is the documention about ArUco markers dictionaries.

The creation of ArUcoMarker pictures from a dictionary is illustrated in the code below:

from argaze.ArUcoMarker import ArUcoMarkerDictionary

# Create a dictionary of specific April tags
aruco_dictionary = ArUcoMarkerDictionary.ArUcoMarkerDictionary('DICT_APRILTAG_16h5')

# Export marker n°5 as 3.5 cm picture with 300 dpi resolution
aruco_dictionary.create_marker(5, 3.5).save('./markers/', 300)

# Export all dictionary markers as 3.5 cm pictures with 300 dpi resolution
aruco_dictionary.save('./markers/', 3.5, 300)

Let's print some of them before going further.

Describe ArUco markers place

Once ArUcoMarker pictures are placed into a scene, it is possible to describe their 3D places into a file.

Wherever the origin point is, all markers places need to be described on a right-handed 3D axis where:

• +X is pointing to the right,
• +Y is pointing to the top,
• +Z is pointing to the backward.

Edit OBJ file description

The OBJ file format could be exported from most 3D editors.

o DICT_APRILTAG_16h5#0_Marker
v 15.000000 0.378741 0.330527
v 20.000000 0.378741 0.330527
v 15.000000 5.120359 -1.255996
v 20.000000 5.120359 -1.255996
f 1 2 4 3
o DICT_APRILTAG_16h5#1_Marker
v 43.500000 31.428055 18.333317
v 48.500000 31.428055 18.333317
v 43.500000 36.428055 18.333317
v 48.500000 36.428055 18.333317
f 5 6 8 7
o DICT_APRILTAG_16h5#2_Marker
v 38.500000 2.678055 5.498381
v 43.500000 2.678055 5.498381
v 38.500000 5.178055 1.168253
v 43.500000 5.178055 1.168253
f 9 10 12 11

Here are some common OBJ file features needed to describe ArUco markers places:

• Object line (starting with the o key) indicates marker dictionary and id by following this format: DICTIONARY#ID_Marker.
• Vertice line (starting with the v key) indicates marker corners. The marker size will be automatically deducted from the geometry.
• Face line (starting with the f key) links vertice and normal indexes together.

Edit JSON file description

the JSON file format allows for the description of marker places using translation and Euler angle rotation vectors.

{
    "dictionary": "DICT_APRILTAG_16h5",
    "places": {
        "0": {
            "translation": [17.5, 2.75, -0.5],
            "rotation": [-18.5, 0, 0],
            "size": 5
        },
        "1": {
            "translation": [46, 34, 18.333],
            "rotation": [0, 70, 0],
            "size": 5
        },
        "2": {
            "translation": [41, 4, 3.333],
            "rotation": [-60, 0, 0],
            "size": 5
        }
    }
}