  We often observe that waves on the surface of shallow water form complex
web-like patterns. They are examples of nonlinear waves, and these patterns are
generated by nonlinear interactions among several obliquely propagating waves.
In this note, we discuss how to construct an exact soliton solution of the KP
equation from such web-pattern of shallow water wave. This can be regarded as
an "inverse problem" in the sense that by measuring certain metric data of the
solitary waves in the given pattern, it is possible to construct an exact KP
soliton solution which can describe the non-stationary dynamics of the pattern.
