function [r, z] = cymbal_point(basis, sfrac)
% CYMBAL_POINT Meridian coordinates (r, z) at an arclength fraction.
nn = length(basis.snode);
s = min(0.999999, max(0, sfrac)) * basis.S;
idx = sum(basis.snode <= s);
idx = min(max(idx, 1), nn - 1);
xi = (s - basis.snode(idx)) / (basis.snode(idx + 1) - basis.snode(idx));
r = basis.rnode(idx) + xi * (basis.rnode(idx + 1) - basis.rnode(idx));
z = basis.znode(idx) + xi * (basis.znode(idx + 1) - basis.znode(idx));
end