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. ![Scene](../../img/scene.png) ## Print ArUco markers from an ArUco dictionary ArUco markers always belong to a set of markers called the ArUco marker dictionary. ![ArUco dictionaries](../../img/aruco_dictionaries.png) 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](https://docs.opencv.org/3.4/d9/d6a/group__aruco.html#gac84398a9ed9dd01306592dd616c2c975). The creation of [ArUcoMarker](../../argaze.md/#argaze.ArUcoMarker.ArUcoMarker) pictures from a dictionary is illustrated in the code below: ```python 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) ``` !!! note There is an **A4_DICT_APRILTAG_16h5_5cm_0-7.pdf** file located in *./src/argaze/ArUcoMarker/utils/* folder ready to be printed on an A4 paper sheet. Let's print some of them before going further. !!! warning Print markers with a blank zone around them to help in their detection. ## Describe ArUco markers place Once [ArUcoMarker](../../argaze.md/#argaze.ArUcoMarker.ArUcoMarker) pictures are placed into a scene, it is possible to describe their 3D places into a file. ![ArUco markers description](../../img/aruco_markers_description.png) Wherever the origin point is, all markers places need to be described on a [right-handed 3D axis](https://robotacademy.net.au/lesson/right-handed-3d-coordinate-frame/) where: * +X is pointing to the right, * +Y is pointing to the top, * +Z is pointing to the backward. !!! warning All ArUco markers spatial values must be given in **centimeters**. ### Edit OBJ file description The OBJ file format could be exported from most 3D editors. ``` obj 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. !!! warning Markers have to belong to the same dictionary. !!! note Markers can have different sizes. ### Edit JSON file description the JSON file format allows for the description of marker places using translation and Euler angle rotation vectors. ``` json { "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 } } } ```