urdf_parser 0.0.4

A urdf parser extension for three_dart that also includes a dae/stl loader.

Flutter URDF-Parser

This library is majorly an extended dart port of https://github.com/gkjohnson/urdf-loaders for the dart three_js port of https://github.com/wasabia/three_dart.

It includes a STL + DAE loader, URDF parser and quaternion + vector3 extension class.

Works with all plattforms that three_dart currently supports. Which are currently Web, iOS, Android, macOS and Windows.

Basic Usage

Requires working three_dart project.

Inside of your initPage() function load your urdf model or dae/stl files.

void initPage() async {
    scene = three.Scene();
    // ...

    // --- STL ---
    three.Object3D stlObject = await STLLoader(null).loadAsync("path to stl file");
    scene.add(stlObject);

    // --- DAE ---
    List<three.Object3D> daeObjects = await DAELoader.loadFromPath('path to dae file', []);
    for (three.Object3D object in daeObjects) {
        scene.add(object);
    }

    // --- URDF ---
    // parse the urdf file to a URDFRobot object
    URDFRobot? robot = await URDFLoader.parse(
        "path to urdf file",
        "path to urdf content folder where stl/dae files are located",
    );

    // create a three_dart recursive object and add it to the scene
    scene.add(robot.getObject());
}

Move joints

In the urdf file defined joints can then be moved via trySetAngle().

robot.trySetAngle("angleName", amount);

Basic example to animate all available joints sequentially

void render() {
    // ...

    double time = DateTime.now().millisecondsSinceEpoch / 6e4;

    List<MapEntry<String, URDFJoint>> joints = (robot!.joints.entries.where(
        (entry) => entry.value.type != "fixed")).toList();

    // robot joint test animation
    double periodicValueSmall = sin((time * joints.length) % 1 * 2 * pi) / 2 + 0.5;
    int s = (time * joints.length).floor() % joints.length;

    // set last angle rotation to 0.5
    int lastS = (s - 1 + joints.length) % joints.length;
    robot!.trySetAngle(
        joints[lastS].key, 
        lerpDouble(joints[lastS].value.lower, joints[lastS].value.upper, 0.5)!,
    );

    robot!.trySetAngle(
        joints[s].key, 
        lerpDouble(joints[s].value.lower, joints[s].value.upper, periodicValueSmall)!,
        );

    // ...
}

Supported Joint Types

• fixed
• continuous
• revolute
• prismatic
• mimic

Supported 3D File Types

• .stl/ .STL (both binary and ascii variants)
• .dae

Additional Features

• Supports color extraction of binary/ ascii stl files, dae files and basic urdf color nodes

Colors Formats

Besides the obvious defined material definition of dae files, also stl files can containt color information. But there is unfortunately no official standard.

Ascii STL Color Format

solid object1
  facet normal 0.0 0.0 0.0
    outer loop
      vertex 1.0 0.0 0.0
      vertex 0.0 1.0 0.0
      vertex 0.0 0.0 1.0
    endloop
  endfacet
endsolid object1=RGB(0,0,255)

solid object2
  facet normal 0.0 0.0 0.0
    outer loop
      vertex -1.0 0.0 0.0
      vertex 0.0 -1.0 0.0
      vertex 0.0 0.0 -1.0
    endloop
  endfacet
endsolid object2=RGB(255,0,0)

If color information is provided then each solid must contain it. Otherwise a default white materials is used for each solid.

Binary STL Color Format

Suuports the "Magics" color format from http://en.wikipedia.org/wiki/STL_(file_format)#Color_in_binary_STL.

Note

As this library is a C# port of https://github.com/gkjohnson/urdf-loaders which was written for Unity. The library contains its own implementation of a hierarchy system using the HierarchyNode class with local/ global transformations. The getObject() function on the URDFRobot class then formats the custom hierarchy implementation to a three_dart group with set children.

And as three_dart uses a coordinate system where the y-axis is facing up, a transformation is performed from the z-axis upwards facing stl/dae formats.