Convert from rvec to quaternion using nalgebra?

[lucasw]

If I get an rvec back from for example opencv::aruco::estimate_pose_charuco_board_def(), how can I convert it to a quaternion (ideally using nalgebra or similar, not the error prone cutting and pasting of a big block of quaternion math code)?

This isn't really an issue with opencv-rust, it may go better in a discussion section if that were enabled here.

I'll probably have it figured out in a little while, and I'll post the answer and maybe it'll save someone else some time.

[lucasw]

I think this is it, but I'll need to test it:

let rslice = rvec.as_slice();
let axisangle = nalgebra::Vector3::new(rslice[0], rslice[1], rslice[2]);
let rot = nalgebra::Rotation3::new(axisangle);
let q = nalgebra::UnitQuaternion::from_rotation_matrix(&rot);
...
pose.orientation.w = q.coords.w;
pose.orientation.x = q.coords.x;
pose.orientation.y = q.coords.y;
pose.orientation.z = q.coords.z;

this appears to be the same as with this python, though multiplied by -1:

import cv2
import numpy as np
from scipy.spatial.transform import Rotation as R

rvec = np.array([0.0064893401728181345, -0.04393382349777288, -1.8669626173081237])
rvec_matrix = cv2.Rodrigues(rvec)[0]
rotation = R.from_matrix(rvec_matrix)
quaternion = rotation.as_quat()

[OlivierLDff]

I find myself often using glam library for this purpose:

let r_vec = glam::Vec3::new(x, y, z);
let quat = glam::Quat::from_scaled_axis(r_vec);
let r_mat = glam::Mat3::from_quat(quat);