An object of the present invention is to provide a method for detecting a shield
in predicting the radio wave propagation characteristics by a technique of the
geometrical optics capable of detecting a content which a ray strikes, at high
rate, when the ray is radiated within the observation space. In the case where
the rays and the contents are given, the projected objects given by the line or
plane are set up, and if an image of the content projected onto the projected object
and an image of the ray projected onto the projected object do not intersect, the
content is excluded from the shield detection object. A plurality of projected
objects i (i=1 to M) are prepared, the selection of shield detection object is
performed for each projected object i in order for i=1 to M, and the content of
the shield detection object is concluded in sequence. Though the conventional method
required the multiple variable equations to be solved for all the contents within
the observation area, this invention allows the multiple variable equations to
be solved only for the concluded contents of the shield detection object. Hence,
the processing time can be shortened.
