  Mathematical theory of an observer is elaborated upon the basis of
A.Poincare's ideas on the nature of geometry and the role of observer's
perceptive space. The said theory is generalizing reference frames theory in
GR. Physical structure (P-structure) and corresponding physical geometry
(P-geometry) notions, representing properties invariance of some physical
objects and their relations, are introduced. P-structure of classical physical
time and its corresponding chronogeometry is considered as an example. Some
quantitative characteristics of observer's visual space geometry are
experimentally determined. The affine model of visual geometry is offered to
interpret experimentally sampled data. The connection of the obtained results
with some problems of theoretical physics is being discussed.
