function ellipse_boundary_points(xc::SVector{2,T},
    theta::Real,
    a,
    b;
    N::Int = 200) where T
    # boday frame points
    thetaB = LinRange(0,2pi, N)
    X=a*cos.(thetaB)
    Y=b*sin.(thetaB)
    x=similar(X)
    y=similar(X)
    for i in 1:length(X)
        xy=body2lab(SVector{2,T}(X[i], Y[i]), xc, theta)
        x[i], y[i]=xy
    end
    return x,y
end


