测绘工程专业英语_测绘工程专业英语重点
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From the discuion thus far it can be stated with absolute certainty that all measured values contain errors , whether due to lack of refinement in reading , instrumental imperfection or human limitations.Some of these errors result from physical conditions that cause them to occur in systematic way , whereas others occur with apparent randomne.Accordingly , errors are claified as either systematic or random.But before defining systematic and random errors , it is helpful to define mistakes.These three terms are defined as follows:
1、Mistake.Mistake or blunders(gro errors)actually are not errors because they usually are so gro in magnitude compared to the other two types of errors.Carelene , inattention , improper training , bad habits ,poor judgement , adverse measuring or observing conditions , and various negative attitudes and emotions are the traces or the common reasons for mistakes.They are not claified as errors and must be removed form any set of observations.Typical example of mistakes are omitting a whole tape length when measuring distance , sighting the wrong target in a round of angles , writing down 27.55 for 25.75 in recording.Therefore great care must be taken to obviate them
Mistakes will never be completely eliminated from measurements , but surveyor's careful , attentive , conscientious attitude can reduce the mistakes in most cases.Through proper training and development of good work habits , development and maintenance of positive attitudes , and understanding the theory and practically eliminated.2、systematic errors.Systematic errors are defined as those errors whose magnitude and algebraic sign can be calculated and applied as a correction to the measured quantity , or these errors follow some physical law and thus can be predicted.Some systematic errorsare removed by some correct measurement procedures(e , g, , balancing backsight and foresight distance in differential leveling to compensate for earth curvature and refraction).Others are removed by deriving corrections based on the physical conditions that were responsible for their creation(e ,g , applying a computed correction for earth curvature and refraction on a trigonometric leveling observation).Surveyors should know how to deal with systematic errors.The first requirement is to recognize and accept the poible existence of errors.Next , identify the various sources that might be affecting a reading systematically , then , determine what the system is.Is it a constant , linear, or in proportion to the size of the quantity being measured ? Or , does it follow some other mathematical relationship ? Is there some physics involved ? Once systematic errors discovered and quantified , the errors can be eentially compensated by certain procees of measuring or correctedto reduce their effect.Careful calibration of all instruments is an eential part of controlling systematic errors3、Random errors.Random(also known as a accident)errors are introduce into each measurement mainly because of human and instrument imperfections as well as uncertainties in determining the effects of the environment on measurements.After all mistakes and systematic errors have been removed from the measured values , the random errors remain.In general , random errors are unavoidable and relatively small.They usually do not follow any physical law , but it can be deal with and estimated according to the mathematical laws of probability.Examples of random errors are(a)imperfect centering over a ground point during distance measurement with an EDM instrument ,(b)bubble not centered at the instant a level rod is read , and(c)small errors in reading graduated scales
Understanding the nature of random errors helps to understand why random errors never really
fully corrected , since the observation of the physical phenomena contains personal , random errors.Thus , measurement have “uncertainties” or random errors that remain unquantifiable.Random errorsare dealt with by controlling or managing them.It is a quality control proce.They cannot be corrected or eliminated , only minimized and controlled.
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测绘工程专业英语课文翻译Unit 18 Construction Layout
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