测绘工程毕业设计外文翻译---水准尺和水准仪(编辑修改稿)

测绘工程毕业设计外文翻译---水准尺和水准仪(编辑修改稿)内容摘要：

ble microwaves and was capable of measuring distances up to 50 mi (80km) or or night. The potential value of these early EDM models to the Surveying profession was immediately recognized: houever, they were expensive and not readily portable for field operations. Furthermore, measuring procedures were lengthy and mathematical reductions to obtain distances from observed values were difficult and timeconsuming. In addition. The range of operation of the first geodimeter was limited in daytime use. Continued research and development have overe all these deficiencies. The chief advantages of electronic surveying are the speed and accuracy with which distances can be measured. If a line of sight is available, long or short lengths can be measured over bodies of water or terrain that is inaccessible for taping. With modern EDM equipment, distance are automatically displayed in digital form in feet or meters, and many have builtin microputers that give results internally reduced to horizontal and vertical ponents. Their many significant advantages have revolutionized surveying procedures and gained worldwide acceptance. The longdistance measurements possible with EDM equipment make use of radios for munication, which is an absolute necessity in modern practice. One syetem for classifying EDMIs is by wavelength of transmitted electromagic energy。 the following categories exist : Electrooptical instruments Which transmit either modulatedlaser or infrared light having wavelengths within or slightly beyond the visible region of the spectrum. Microwave equipments Which transmits microwaves with frequencies in the range of 3 to 35 GHz corresponding to wavelengths of about to mm. Another classification system for EDMIs is by operational range . It is rather subjective , but in general two divisions fit into this system : short and medium range .The shortrange group includes those devices whose macimum measuring capability does not exceed about 5km . Most equipment in this division is the electro –optical type and uses infrared light . These instruments are small, portable, easy to operate, suitable for a wide variety of field surveying work, and used by many practitioners. Instruments in the mediumrange group have measuring capabilities extending to about 100 km and are either the electrooptical (using laser light) or microwave type. Although frequently used in precise geodetic they are also suitable for land and engineering surveys. Longerrange device also available can measure lines longer than 100km,but they are nit generally used in ordinary surveying work. Most operate by trasmitting long radio waves, but some employ microwaves. They are used primarily in oceanogaraphic and hydrograpgic sur。