1. Field of the Invention
The present invention relates to an object detector.
2. Description of the Related Art
A laser radar has been known as an in-vehicle device that detects the presence or absence of an object in front of a moving vehicle, and that detects a distance to the object.
A laser radar is a device that detects the presence or absence of an object in a desired range, and that detects a distance to the object. In order to detect an object or a distance to the object, the laser radar irradiates a laser beam emitted from a light source (a laser diode) onto the object, while scanning the laser beam by a rotating mirror, and the laser radar detects reflected light or scattered light from the object with a photo detector. As a photo detector, an avalanche photodiode is utilized, for example.
In a detection range, there exists a minimum detectable angular range (which is referred to as “angular resolution,” hereinafter). When, in the detection range, a main scanning direction is defined to be a direction in which a laser beam is to be scanned, and a sub-scanning direction is defined to be a direction which is perpendicular to a plane formed by scanning the laser beam, the angular resolution in the main scanning direction is different from the angular resolution in the sub-scanning direction.
Though the angular resolution depends on various conditions, such as performance of the photo detector, or reflectivity of an object, in general, the angular resolution is defined to be a range of an object which can be detected by single pulse scanning. Here, “the range of the object which can be detected by the single pulse scanning” means a region in a detection range in which an image of a light source overlaps with an image of a photo detector.
For example, even if a particular region is within a region of an image of a light source, namely, the particular region is in a range which is irradiated by the light source, if the particular region is out of a region detectable by the photo detector, reflected light from the particular region is not guided to the photo detector. Thus, the reflected light from the particular region is not detected. Conversely, if a particular region is within a region detectable by a photo detector, but the particular region is out of a region of an image of a light source, the particular region is not irradiated by the light source. Thus, neither reflected light nor scattered light is generated in this case.