  Solar filaments show the position of large scale polarity inversion lines and
are used for the reconstruction of large-scale solar magnetic field structure
on the basis of H{\alpha} synoptic charts for the periods when magnetographic
measurements were not available. Sometimes crossing filaments are seen in
H{\alpha} filtergrams. We analyze daily H{\alpha} filtergrams from the archive
of Big Bear Solar Observatory for the period of 1999-2003 to find crossing and
interacting filaments. A number of examples are presented and filament patterns
are compared with photospheric magnetic field distributions. We have found that
all crossing filaments reveal quadrupolar magnetic configurations of the
photospheric field and presume the presence of null points in the corona.
