The absorption coefficient and refractive index of the tourmaline in different directions have been firstly characterized by the terahertz time-domain spectroscopy. Results show that the absorption and refractive index of terahertz are much related with the tourmaline structure. And the absorption along the optical axis direction is more sensitive than that of the vertical direction. Such a result indicates that the identification and characterization of crystals as well as minerals can be realized by the THz method.
An automatic large-scale 3D coordinate measurement system based on vision guidance is presented. With a high-accuracy total station accomplishing the basic coordinate measurement, a camera mounted on the total station is used to scan the measuring field. The camera can identify the target in the viewing field and provide its azimuth information for the total station to aim at it automatically. Thus high-accuracy non-contact measurement can be accomplished without additional effort for targeting. The results showed that the measurement system can realize automatic large-scale measurement precisely and efficiently which provides an efficient approach for solving automatic large-scale measurement problems.
Geometric errors in laser trackers such as light offset and transit tilt have essential influence on the system measurement errors. Thus error detection and calibration are very important for producers and customers to execute error compensation. Different methods are developed to detect and calibrate errors. However, the commonly used methods such as length measurement and two-face measurement are sensitive to several misalignments which cannot calibrate errors directly and separately. In this paper a series of methods for detecting and calibrating geometric errors such as mirror tilt, beam tilt and transit tilt were presented which can calibrate geometric errors individually and precisely. The mirror tilt could be detected with the help of two autocollimators and one polygon. Then the beam tilt and offset errors were calibrated using a CCD camera and condenser lenses. Finally the transit tilt error was calibrated using a gradient and a vertical plane. Experiments and error assessment were executed to show that the accuracy of the calibration methods can meet the user’s demand.
A novel method was proposed to measure the tilt error between the transit axis and standing axis of the laser tracker. A gradienter was first used to make the standing axis of the laser tracker perpendicular to the horizontal plane. The laser beam of the tracker was then projected onto a vertical plane set at a certain distance from the tracker with equal horizontal angles and diverse vertical angles in two-face mode. The contrail of the laser beam was recorded while the simulation was manipulated to estimate the beam trail under the same circumstance. The tilt error was thus obtained according to the comparison of the actual result against the simulated one. Experimental results showed that the accuracy of the tilt measuring method could meet the user’s demand.
The working principle and system design of the laser tracker measurement system are introduced, as well as the key technologies and solutions in the implementation of the system. The design and implementation of the hardware and configuration of the software are mainly researched. The components of the hardware include distance measuring unit, angle measuring unit, tracking and servo control unit and electronic control unit. The distance measuring devices include the relative distance measuring device (IFM) and the absolute distance measuring device (ADM). The main component of the angle measuring device, the precision rotating stage, is mainly comprised of the precision axis and the encoders which are both set in the tracking head. The data processing unit, tracking and control unit and power supply unit are all set in the control box. The software module is comprised of the communication module, calibration and error compensation module, data analysis module, database management module, 3D display module and the man-machine interface module. The prototype of the laser tracker system has been accomplished and experiments have been carried out to verify the proposed strategies of the hardware and software modules. The experiments showed that the IFM distance measuring error is within 0.15mm, the ADM distance measuring error is within 3.5mm and the angle measuring error is within 3〞which demonstrates that the preliminary prototype can realize fundamental measurement tasks.
Spatial coordinate measurement systems such as theodolites, laser trackers and total stations have wide application in
manufacturing and certification processes. The traditional operation of theodolites is manual and time-consuming which
does not meet the need of online industrial measurement, also laser trackers and total stations need reflective targets
which can not realize noncontact and automatic measurement. A new automatic guided laser theodolite system is
presented to achieve automatic and noncontact measurement with high precision and efficiency which is comprised of
two sub-systems: the basic measurement system and the control and guidance system. The former system is formed by
two laser motorized theodolites to accomplish the fundamental measurement tasks while the latter one consists of a
camera and vision system unit mounted on a mechanical displacement unit to provide azimuth information of the
measured points. The mechanical displacement unit can rotate horizontally and vertically to direct the camera to the
desired orientation so that the camera can scan every measured point in the measuring field, then the azimuth of the
corresponding point is calculated for the laser motorized theodolites to move accordingly to aim at it. In this paper the
whole system composition and measuring principle are analyzed, and then the emphasis is laid on the guidance
methodology for the laser points from the theodolites to move towards the measured points. The guidance process is
implemented based on the coordinate transformation between the basic measurement system and the control and
guidance system. With the view field angle of the vision system unit and the world coordinate of the control and
guidance system through coordinate transformation, the azimuth information of the measurement area that the camera
points at can be attained. The momentary horizontal and vertical changes of the mechanical displacement movement are
also considered and calculated to provide real time azimuth information of the pointed measurement area by which the
motorized theodolite will move accordingly. This methodology realizes the predetermined location of the laser points
which is within the camera-pointed scope so that it accelerates the measuring process and implements the approximate
guidance instead of manual operations. The simulation results show that the proposed method of automatic guidance is
effective and feasible which provides good tracking performance of the predetermined location of laser points.
The problem of efficient use of multi-temporal remotely sensed data for land-cover and landscape pattern dynamics has
already considerable attention in landscape ecology and some other disciplines. This research develops and tests a
methodological approach to monitor and analysis landscape dynamics change of Yongding river watershed (Mentougou
section) as study area from 1988 to 2005, The result shows that the OIF is the best method of optimal bands selection in
Landsat TM remote sensing data, TM3, 4, 5 bands is optimal band combination ;the Mentougou Reach of Yongding
river watershed landscape changed significantly in terms of its composition over the period 1988-2005, The total
landscape patches of study area in 2005 are more those in 1988,2001, Mean patch size(MPS)decreased sharply, Number
of patches(NP) increased sharply, The landscape pattern takes on the fragmentation trends under the effect on the human
activity. The forest (woodland and shrubland)are the main landscape matrix. with a significant decrease in croplands and
a increase in built-up (residential, urban land) and industrial minerals mining land(coal, open-pit)over the 17 years, And
the underlying socio-economic and other drivers of landscape change in study area are discussed.