The present invention relates to a measuring method and a measuring instrument to measure a multiple number of points periodically or continuously over time.
For the purpose of observing the sinking of ground, of observing landslide, of observing displacement of banks and walls of construction work such as a dam, of observing displacement of wall surface of a tunnel, measurement is performed periodically or continuously over time by using a measuring instrument on a multiple number of measuring points, which are set up in a measurement range.
For instance, in case where a tunnel is to be constructed to build underground railway, for the purpose of observing whether ceiling and wall surface of the tunnel constructed may not be displaced or not, a multiple number of prisms are installed on the ceiling and on the wall surface as targets, and positional displacement of all these prisms are measured one after another without operator intervention by using a measuring instrument (hereinafter, this is referred as “monitoring measurement”).
When the monitoring measurement is performed, the measuring instrument automatically searches the prisms, i.e. the measuring points, performs sighting, measures distances, and carries out the measuring operation. In order to acquire initial values to search the measuring points thus set up, it is necessary to carry out teaching operations on each of the measuring points.
In a conventional teaching operation, an operator performs sighting each of the measuring points by using a measuring instrument, measures a horizontal angle, a vertical angle and a distance with respect to each of the measuring points, performs three-dimensional measurement with respect to each of the measuring points and sets up the obtained results of the measurement as initial values of each measuring point respectively. According to this method, the operator measures the measuring points one by one. Further, because a view angle of a sighting telescope provided on the measuring instrument is narrow, much time is required for sighting and the working efficiency is low. As a result, much time is required. In particular, in case where the time for the measuring operation is limited, e.g. in case where the operation is performed in a tunnel for underground railway, the measuring operation must be finished during the time period when the railway is not in operation in order to perform monitoring measurement on ceiling and wall surface of the tunnel, and so the measuring time is required to be shortened.
Or, there is an another method as follows. The measuring instrument comprises a wide-angle camera and takes the images of the measurement range by the wide-angle camera. Then, the measuring instrument extracts the measuring points from the acquired images through images processing, detects positions of the measuring points. Based on the positions of the measuring points obtained from the images, the measuring instrument performs sighting of the measuring points, and after the sighting, the measuring instrument measures a horizontal angle, a vertical angle and a distance with respect to each of the measuring points.
In this case, if the range of image pickup is extended in wider range or if a measuring point is at a long distance, the accuracy to detect the measuring point is decreased. Also, optical axis of the wide-angle camera and the telescope of the measuring instrument are offset, and it is necessary to correct the results detected by the wide-angle camera. The amount of correction is a function of the distance, and if the detection of the measuring point in the image processing is not associated with distance measurement, the accuracy is decreased. For this reason, there have been problems in the past that sighting by the measuring instrument cannot be performed.