In general, a distance refers to a length of a straight line linking two points with each other.
In order to measure the distance, after dividing the straight line between two points into several sections, the length of each section is measured by using a scaled ruler or a reference ruler having a predetermined distance and the total lengths of the sections are obtained. The distance is calculated by using the total length.
Further, in addition to the above scheme, there are generally-known various schemes such as a triangulation scheme of directly and mechanically measuring included angles placed at both ends of a scale, which has a predetermined length and placed between two measurement points, by using a theodolite telescope, a scheme of measuring the distance by reading scale intervals between two scribed lines on an image viewed through a telescope, and a scheme of calculating the distance based on the speed and the time of light or an electromagnetic wave.
According to the scheme of measuring the distance between two points using the reference ruler such as the ruler, since a measurer must personally measure the length of each section to calculate the distance, the measurement efficiency and precision may be significantly degraded.
According to the distance measuring scheme based on a telescope, the high cost is required. In addition, since the measurer must read the scale intervals between two scribed lines to calculate the distance, errors may frequently occur when the distance is measured.