function q = Euler(p, theta)
    % q = Euler(p, theta) is the quaternion for rotation about
    % point p with Euler angles theta = [tx,ty,tz] in degrees.
    c = cosd(theta/2);
    s = sind(theta/2);
    rx = qtn([c(1) s(1) 0 0]);
    ry = qtn([c(2) 0 s(2) 0]);
    rz = qtn([c(3) 0 0 s(3)]);
    r = rz*ry*rx;
    p = qtn([0 p]);
    q = r*p/r;
end