1.  Field of the Invention
The present invention relates to a three-dimensional monitoring apparatus suitable for use of detecting a human body coming into, for example, a dangerous area in a production line or an industrial machine and the like in a factory, more specifically, to a three-dimensional monitoring apparatus capable of acquiring position information of an incoming object into a predetermined three-dimensional space to be monitored by using pattern light as a carrier. 
2.  Description of the Background Art
In recent years, cases bringing a monitoring apparatus for detecting the presence or absence of an incoming object in a predetermined area (a three-dimensional space to be monitored) into a factory and the like have been increased in number for the purposes of preventing operators from being suffered from inclusion accidents due to a variety of equipment and preventing equipments from being damaged due to a sudden incoming of the object. 
As for a monitoring apparatus, an area sensor monitoring a predetermined plane by using continuance of a plurality of light beams and a laser-scanning-type sensor monitoring a predetermined plane with scanning laser beams by using a polygon mirror and the like are well known.  With using these apparatuses, for example, when the incoming object is detected, it also becomes possible to perform automatic control such as 97 immediately stop of the equipments. 
However, these conventional sensors (monitoring apparatuses) have been predicated on so called ‘two-dimensional plane monitoring’ developing a virtual light detecting surface on a space to be monitored by illuminating and generating an output by reacting only objects crossing (blocking) the detecting surface, so that we would have to say that these apparatuses have not been suitable for monitoring of an arbitrary three-dimensional space to be monitored.  That is to say, even in monitoring the arbitrary three-dimensional space to be monitored, there are problems such that only the presence of the incoming of an object from a side in which the light detecting surface has been developed can be monitored (detected) actually and it is impossible to react to an object and the like incoming into the predetermined space to be monitored without passing through the light detecting surface to be monitored. 
Furthermore, the conventional sensors basically detect only the presence or the absence of an object blocking the light detecting surface and it is quite impossible to match user's requests even for detecting a state of incoming of the object into the predetermined space to be monitored (for example, how far the object has entered into the predetermined space to be monitored).