  Non-axisymmetric forces are presented for 107 spiral galaxies using the 2
Micron All Sky Survey (2MASS) images. We apply both Cartesian integration and a
polar grid integration utilizing a limited number of azimuthal Fourier
components of density. We found that bar strength is independent of the method
used to evaluate the gravitational potential. However, the polar method is more
suitable for weak and noisy images. Bar strength was found to be sensitive to
the Hubble-type dependent scale height of the disk, which has been ignored in
the previous studies. On the other hand, the method is rather insensitive to
the vertical model of the disk, as long as a same vertical dispersion is
assumed, or to the boxy/peanut shaped structure, studied in terms of
non-constant vertical scale height along the disk. In the near-IR most galaxies
in our sample show non-axisymmetric forces in some level, and 40 percent of
them have bars in a sense that they have regions with a constant phase of the
m=2 Fourier density component.
