  This paper reports recent lattice characterization results obtained at the
National Synchrotron Light Source II (NSLS-II) storage ring, conducted without
reliance on a lattice model. A pair of beam position monitors (BPMs) with
bunch-by-bunch (B$\times$B) resolution, were recently installed in a section of
the storage ring free of magnetic fields. The new BPM pair measured the beam,
or bunch's transverse Poincar\'e map precisely after the beam was excited.
Linear one-turn-matrices (OTM) were then derived, and from these, the
4-dimensional coupled Twiss parameters were extracted at the locations of the
BPM pair. By normalizing beam oscillation amplitudes with the Twiss parameters,
the global action-variables were obtained. These action-variables facilitated
the measurement of the local Twiss parameters observed by other BPMs
independent on lattice model. This method is general, and particularly useful
in certain scenarios such as a round beam mode in a diffraction-limited light
source ring. We applied it to assess both weakly and strongly coupled lattices
at the NSLS-II ring. Through analysis of the strongly coupled lattice, the
quadrupole tilt errors were estimated to be less than 400 \si{\mu}rad.
Utilizing the BPMs' B$\times$B resolution, for the first time we observed the
variations of the linear lattice along a long bunch-train.
