dynibo 0.5.2

Tree-structured robot kinematics and dynamics with runtime-size workspace APIs
Documentation 
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use nalgebra::{Matrix3, Vector3};

/// Identity and immutable inertial properties of one URDF link.
#[derive(Clone, Debug, PartialEq)]
pub(crate) struct Link {
    name: String,
    dynamics: LinkDynamics,
}

#[derive(Clone, Copy, Debug, PartialEq)]
pub(crate) struct LinkDynamics {
    pub(crate) mass: f64,
    pub(crate) center_of_mass: Vector3<f64>,
    pub(crate) inertia: Matrix3<f64>,
    pub(crate) first_moment: Vector3<f64>,
    pub(crate) origin_inertia: Matrix3<f64>,
}

impl Link {
    /// Creates a link from its immutable inertial properties.
    pub(crate) fn new(
        name: impl Into<String>,
        mass: f64,
        center_of_mass: Vector3<f64>,
        inertia: Matrix3<f64>,
    ) -> Self {
        let first_moment = mass * center_of_mass;
        let origin_inertia = inertia
            + mass
                * (center_of_mass.norm_squared() * Matrix3::identity()
                    - center_of_mass * center_of_mass.transpose());
        Self {
            name: name.into(),
            dynamics: LinkDynamics {
                mass,
                center_of_mass,
                inertia,
                first_moment,
                origin_inertia,
            },
        }
    }

    /// Returns the link name loaded from the URDF.
    pub(crate) fn name(&self) -> &str {
        &self.name
    }

    /// Returns the link mass in kilograms.
    pub(crate) const fn mass(&self) -> f64 {
        self.dynamics.mass
    }

    /// Returns the center of mass expressed in the link frame, in metres.
    pub(crate) const fn center_of_mass(&self) -> &Vector3<f64> {
        &self.dynamics.center_of_mass
    }

    /// Returns the rotational inertia about the center of mass in the link frame.
    pub(crate) const fn inertia(&self) -> &Matrix3<f64> {
        &self.dynamics.inertia
    }

    pub(crate) const fn dynamics(&self) -> LinkDynamics {
        self.dynamics
    }
}

#[cfg(test)]
#[cfg_attr(coverage_nightly, coverage(off))]
mod tests {
    use approx::assert_relative_eq;
    use nalgebra::{Matrix3, Vector3};

    use super::Link;

    #[test]
    fn link_precomputes_first_moment_and_origin_inertia() {
        let mass = 2.5;
        let center = Vector3::new(0.3, -0.2, 0.4);
        let inertia = Matrix3::new(1.2, 0.1, -0.2, 0.1, 1.5, 0.05, -0.2, 0.05, 1.8);
        let link = Link::new("body", mass, center, inertia);
        let dynamics = link.dynamics();

        let expected_first_moment = mass * center;
        let expected_origin_inertia = inertia
            + mass * (center.norm_squared() * Matrix3::identity() - center * center.transpose());
        assert_relative_eq!(
            dynamics.first_moment,
            expected_first_moment,
            epsilon = 1.0e-14
        );
        assert_relative_eq!(
            dynamics.origin_inertia,
            expected_origin_inertia,
            epsilon = 1.0e-14
        );
    }
}