测绘专业英语翻译

Unit1 What is Geomatics? 3页
Data plotting (presentation) is handled through the use of mapping and other illustrative computer programs; the presentations are displayed on computer screens (where interactive editing can occur) and are output on paper from digital plotting devices. 数据绘图（描述，表达）是通过使用绘图和其他示范的计算机程序；这种表达显示在电脑屏幕（可以进行交互式编辑）和通过数字绘图设备输出到纸上。

Once the positions and attributes of geographic entities have been digitized and stored in computer memory, they are available for use by a wide variety of users. Through the use of modem information technology (IT), geomatics brings together professionals in the following disciplines: surveying, mapping, remote sensing, land registration, civil and marine engineering, forestry, agriculture, planning and development, geology, geographical sciences, infrastructure management, navigation, environmental and natural resources monitoring, and computer science.
Other Definitions of Geomatics.一旦地理实体的位置和属性已被数字化并存储在计算机的内存中，它们即可以被各种各样的用户使用。

通过使用现代信息技术（IT），测绘学汇集了以下学科的专业人员：测量，绘图，遥感，土地登记，土木和海洋工程，林业，农业，规划和开发，地质，地理科学，基础设施管理，导航，环境和自然资源的监测，与计算机科学。

As defined by the Canadian Institute of Geomatics in their quarterly journal"
Geomatica":Geomatics is a field of activities which, using a systemic approach, integrates all the means used to acquire and manage spatial data required as part of scientific, administrative, legal and technical operations involved in the process of the production and management of spatial information. 在加拿大地理信息研究所在其季刊杂志“geomatica”中的定义为：测绘学是一个活动领域，它使用系统的方法，将所有的手段来获取和管理要求的空间数据，比如空间信息生产和管理过程中包含的科研，行政，法律和技术操作的部分数据
The definition of Geomatics is evolving. A working definition might be "the art, science and technologies related to the management of geographically-referenced information." Geomatics includes a wide range of activities, from the acquisition and analysis of site-specific spatial data in engineering and development surveys to the application of GIS and remote sensing technologies in environmental management. It includes cadastral surveying, hydrographic surveying, and ocean mapping, and it plays an important role in land administration and land use management.。

测绘学的定义是不断变化的。

一个工作定义可能是“与地理参照信息管理有关的艺术，科学和技术。

”测绘学包括一个范围广泛的活动，从工程和开发测绘中特定地点的空间数据的采集和分析到地理信息系统和遥感技术在环境管理中的应用。

它包括地籍测量，水道测量，海洋测绘，并在土地管理和土地利用管理中发挥了重要作用。

Geomatics is the modern scientific term referring to the integrated approach of measurement, analysis, management, storage and display of the descriptions and location of Earthbased data, often termed spatial data.测绘学是现代科学术语，指的是地球基础数据（通常被称为空间数据）的描述和位置的测量，分析，处理，存储和显示的综合办法These data come from many sources, including earth orbiting
satellites, air and sea-borne sensors and ground based instruments. It is processed and manipulated with state-of-the-art information technology using computer software and hardware. It has applications in all disciplines which depend on spatial data, including environmental studies, planning, engineering, navigation, geology and geophysics, oceanography, land development and land ownership and tourism. It is thus fundamental to all the geoscience disciplines which use spatially related data.
它已被应用于依赖空间数据的所有学科，包括环境研究，规划，工程，导航，地质学和地球物理学，海洋学，土地开发和土地所有权和旅游业。

它因此成为利用空间相关数据的一切地球科学学科的基础。

Unit 2 Geodetic Surveying and Plane Surveying大地测量与平面测量6页Surveying has been traditionally defined as the art and science of determining the position of natural and artificial features on, above or below the earth’s surface; and representing this information in analog form as a contoured map, paper plan or chart, or as figures in report tables, or in digital form as a three dimensional mathematical model stored in the computer. （测量传统定义为确定地表、地下和地上的自然与人工地貌特征；并使之按比例测绘成地形图平面图或图表，或形成报告图表，或以数字形式形成三维立体数学模型存储进计算机。

）
As such, the surveyor/geodesist dealt with the physical and mathematical aspect of measurement. （同样的，测量员/大地测量学家处理的就是测量出的物理的和数学的特征）
The accurate determination and monumentation of points on the surface of the Earth is therefore seen as the major task. （因此精确确定并标定地表点位便成为测量的主要任务）
Though these surveys are for various purposes, still the basic operations are the same---they involve measurements and computations or, basically, fieldwork and office work. （虽然测量工作有不同目的，基本的操作却都一样――他们包括测量和计算，或更基本地称之为，外业工作和内业工作）
There are many different types of surveys such as land surveys, route surveys, city surveys, construction surveys, hydrographic surveys, etc., but generally speaking, surveying is divided into two major categories: geodetic and plane surveying. （测量分为许多不同的类型，如土地测量，路线测量，城市测量，建筑测量，水道测量等等，但是总的来说，测量分为两个主要的种类：大地测量和平面测量）
Surveys will either take into account the true shape of the Earth（Geodetic surveys）or treat the earth as a flat surface(Plane surveys). （是考虑地球真实形状的大地测量还是将地球当成一个平面的平面测量【紧跟着上句】）Additionally, surveys are conducted for the purpose of positioning features on the ground(Horizontal surveys), determining the elevation or heights of features(Vertical surveys) or a combination of both.（另外，测量还分为确定平面位置的水平测量和确定海拔的高程测量或两者的综合。

）Geodetic Surveying（大地测量）
The type of surveying that takes into account the true shape of the earth
is called geodetic surveying. （考虑地球真实形状的测量工作称为大地测量）This type of survey is suited for large areas and long lines and is used to find the precise location of basic points needed for establishing control for other surveys. （这种测量适用于大范围和长距离的测量工作，用来确立基本点的精确位置，用以建立其他测量工作所需的控制网。

）
In geodetic surveys, the stations are normally long distances apart, and more precise instruments and surveying methods are required for this type of surveying than for plane surveying.（在大地测量中，站点经常是互相距离很远，那么这种测量就比平面测量需要更精确的仪器和测量方法。

）
Widely spaced, permanent monuments serve as the basis for computing lengths and distances between relative positions. （广泛间隔开的永久标石就作为计算点位之间距离的基础）
These basic points with permanent monuments are called geodetic control survey points, which support the production of consistent and compatible data for surveying and mapping projects.（这种永久标石点被称为大地控制点，为测量和绘图工作提供可靠和一致的数据）
In the past, ground-based theodolites, tapes, and electronic devices were the primary geodetic field measurements used. （过去，大地经纬仪、卷尺和电子设备是大地测量的野外工作初时的工具。

）
Today, the technological expansion of GPS has made it possible to perform extremely accurate geodetic surveys at a fraction of the cost. （现在，GPS技术的发展使大地测量工作花费非常小的代价就能获得极为精确的结果成为可能。

）
A thorough knowledge of the principles of geodesy is an absolute prerequisite for the proper planning and execution of geodetic surveys.（大地测量工作计划的编制和实施，绝对需要对大地测量学知识有全面的掌握。

）In Geodetic Surveys, the shape of the earth is thought of as a spheroid, although in a technical sense, it is not really a spheroid. （在大地测量中，地球的形状被看成一个椭球体，虽然在技术角度来看，它不是真正的椭球。

）
Unit 3 Distance Measurement（距离测量）11+13页
One of the fundamentals of surveying is the need to measure distance.（测量工作的一项基础是距离测量）Distances are not necessarily linear, especially if they occur on the spherical earth.（距离不一定指的是直线的，尤其是在地球曲面上的距离）In this subject we will deal with distances in Euclidean space, which we can consider a straight line from one point or feature to another. （这里，我们所涉及的是欧几里德空间，我们可以认为一条从一点到另一点或一个特征到另一个特征的线是直线。

）Distance between two points can be horizontal, slope, or vertical. （两点之间的距离可以是平距、斜距、或者是垂距。

）Horizontal and slope distances can be measured with lots of techniques of measurement depending on the desired quality of the result. （根据测量结果的精度要求不同，平距或斜距有多种测量方法）If the points are at different elevations, then the distance is the horizontal length between plumb lines at
the points. （如果这些点在不同高程上，那么平距指的是过点的垂线之间的水平长度。

）Here gives a brief summary of relevant techniques and their respective accuracies:（这里给出一个简短的相关技术的摘要和它们各自的精度）
Pacing and Odometer（步测和自动计程仪）
Pacing is a very useful form of measurement though it is not precise, especially when surveyors are looking for survey marks in the field.（虽然不精确，但步测是一个非常有用的测量方法，尤其是测量者在野外寻找测量标志时。

）Pacing can be performed at an accuracy level of 1/100~1/500 when performed on horizontal land, while the accuracy of pacing can’t be relied upon when pacing up or down steep hills.（当在水平场地进行时，步测可以达到1/100到1/500的相对精度，而当地面起伏较大时，这样的精度就不能保证了。

）The odometer is a simple device that can be attached to any vehicle and directly registers the number of revolutions of a wheel.（自动计程仪是一个简单的装置，可以附属于车辆之上并直接记录轮子的旋转周数。

）With the circumference of the wheel known, the relation between revolutions and distance is fixed. （由于知道了轮子的周长，转数和距离之间的关系就确定下来）Ordinary Taping and Precise Taping（普通尺距测量和精密尺距测量）
Taping is a very common technique for measuring horizontal distance between two points.（尺距测量是测量两点之间平距的非常普遍的方法。

）Ordinary taping refers to the very common tapes that we can buy them in stores, such as the plastic tapes or poly tapes.（普通尺距测量使用的是我们可以在商店里买到的非常普遍的的尺子，例如塑胶尺或涤纶尺。

）Such tapes have low precision in distance measurements with about 1/3000~1/5000.（这种尺的精度低，测距精度只有1/3000到1/5000）The precise taping refers to the steel tapes and which are much more expensive than the plastic tape and have higher precision of 1/10000~1/30000.（精密尺距测量使用的是比塑胶尺贵的多的钢尺，并具有更高的精度――1/10000到1/30000）Invar tapes are composed 35% nickel and 65% steel.（因瓦尺是由35％的镍和65％的钢组成）This alloy has a very low coefficient of thermal expansion, making the tapes useful in precise distance measurement. （这种合金具有非常低的热膨胀系数，使得这种尺利于精密距离测量）Many tapes are now graduated with foot units on one side and metric units on the reverse side.（现在许多尺上都在正面标刻了英尺计量单位，而在反面标刻了米制计量单位）Metric units are in meters, centimeter and minimeter with the total length of 20 m, 30 m, 50 m and 100 m.（米制计量单位是米，厘米和毫米，尺的总长为20m、30m、50m或100m）
Electronic Distance Measurement(EDM) （电子测距仪）
The Electronic Distance Measurement(EDM) was first introduced in 1950s by the founders of Geodimeter Inc.（电子测距仪的概念是由Geodimeter公司的创始人在20世纪50年代引入的。

）The advent of EDM instrument has completely revolutionized all surveying procedures, resulting in a change of emphasis and techniques.（EDM测量手段的出现是对所有测量手段的完全的革命，导致了一场技术革命和侧重点的改变。

）Distance can now be measured easily, quickly and with great accuracy, regardless of terrain conditions.（现在距离可以被很容易、快速和精确的测量，而又不受地形影响。

）EDM instruments refer to the distance measurement equipments using light and radio waves.（EDM 是利用光波和无线电波测距的设
备）Both light waves and radio waves are electromagnetic.（光波和无线电波都是电磁波）They have identical velocities in a vacuum (or space) to 299,792.458±0.001km/sec. （它们在真空中都有一样的速度299,792.458±0.001km/sec）These velocities, which are affected by the air’s density, are reduced and need to be recalculated in the atmosphere.（它们的速度，由于会收到空气密度的影响而降低，在大气中需要重新计算）The basic principle of EDM instruments is that distance equals time multiplied by velocity. （EDM的基本原理是距离等于时间乘速度）Thus if the velocity of a radio or light wave and time required for it to go from one point to another areknown, the distance between the two points can be calculated.（这样，如果无线电波或光波的速度和其从一点到另一点所需的时间已知了，两点之间的距离就可以计算出来）The EDM instruments may be classified according to the type and wavelength of the electromagnetic energy generated or according to their operational range.（可以依照产生的电磁能量的类型和波长或根据它们的运作范围给EDM分类。

）EDM instruments use three different wavelength bands: (1)Microwave systems with range up to 150km, wave length 3 cm, not limited to line of sight and unaffected by visibility; (2)Light wave systems with range up to 5 km (for small machines), visible light, lasers and distance reduced by visibility;
(3)Infrared systems with range up to 3 km, limited to line of sight and limited by rain, fog, other airborne particles.（EDM使用三种不同波长的波段：(1)微波系统，其测距范围达150km，波长3cm，不受限于视线范围，也不受可见度的影响；(2)可见光波段，有效范围5km（小型仪器），可见光、激光，其距离受可见度的影响会降低；(3)红外线波段，测程3km，受限于视线范围，并且受限于空气中的微粒影响）Although there is a wide variety of EDM instruments available with different wavelengths, there are basically only two methods of measurement employed which may divide the instruments into two classification as electro-optical (light waves) and microwaves (radio waves) instruments.（尽管不同的EDM用到不同的波长，基本上只有两种测量方法在使用，可以将其分为光电测距仪和微波测距仪）These two basic methods are namely the pulse method and more popular phase different method.（这两种基本方法即脉冲法和更流行的相位法）They function by sending light waves or microwaves along the path to be measured and measuring the time differences between transmitted and received signals, or in measuring the phase differences between transmitted and received signals in returning the reflecting light wave to source. （沿着要测的路径发射光波或微波，并测出发射和收到反射信号之间的时间间隔，或者是测出发射和接受反射信号之间的相差，它们通过这种方法来运行）Modern EDM instruments are fully automatic to such an extent that, after the instruments, set up on one station, emits a modulated light beam to a passive reflector set up on the other end of the line to be measured.（现代的EDM全自动化到这样的程度，在一个站点安置，需测距离线的另一处安置有反射棱镜，发射一束已调制的光束到棱镜上）The operator need only depress a button, and the slope distance is automatically displayed. （操作者仅仅需要按一个键，斜距就自动显示出来。

）More complete EDM instruments also have the capability of measuring horizontal and vertical or zenith angles as well as the slope distance. （更完全的EDM还具有测水平角、竖直角和天顶角的功能）
These instruments referred to as total station instruments. （这种仪器被称为全站仪）
Unit 4 Angle and Direction Measurement（角度和方向测量）18页
These readouts can be recorded in a conventional field book or can be stored in a data collector forfuture printout or computation.（这些显示可以被一个传统的野外电子手簿或数据收集器记录，以便日后打印或计算）
The instrument contains a pendulum compensator or some other provision for indexing the vertical circle readings to an absolute vertical direction.
（这种仪器具有一个悬挂补偿器或其它装置，使竖盘指标读数指向一个绝对竖直方向）
The circle can be set to zero readings by a simple press of a button or initialized to any value on the instrument.（这个度盘可以通过简单的按一个键就将其置零，或初始化成任一值）
Azimuth is the horizontal angle measured in a clockwise direction from the plane of the meridian, which is a line on the mean surface of the earth joining the north and south poles. （方位角是从子午面起算按顺时针旋转的角，子午线是在地球平均表面连接北极与南极的线）
Azimuth ranges in magnitude from 0°to 360°, values in excess of 360°, which are sometimes encountered in computations, are simply reduced by 360°before final listing.（方位角的取值范围从0度到360度，超过360的值――有时会在计算时遇到，只需减去360度即可）
Bearing is the traditional way of stating the orientation of the line.（方向角是一种传统的描述直线方向的方法）
It is actually the angle measured from the north or south.（实际上，它是从南或北方向开始量测的角）
The bearing, which can be measured clockwise or counterclockwise from the north or south end of the meridian, is always accompanied by letters that locate the quadrant in which the line falls.（方向角可以从子午线北端或南端以顺时针或逆时针量测，总是伴以字母，用来标明直线所落在的象限）
For example, bearing N32W indicates a line trending 32°west of the north. （例如：方向角N32W代表一条直线从北方向转向西方向32度）
It is equal to an azimuth of 328°.（它等于方位角328度）
Bearing S12W indicates a line trending 12°west of the south. （方向角S12W代表一条直线从南方向转向西方向12度）
It is equal to an azimuth of 192°.（它等于方位角192度）
It is important to state that the bearing and azimuth are respect to true north.（需要重点说明的是，方向角和方位角所用的是真北方向。

）
Unit 5 Traversing （导线测量）21页
Trilateration possesses some advantages over triangulation because the measurement
of the distances with EDM instrument is so quick, precise and economical while the measurement of the angles needed for triangulation may be more difficult and expensive.（三边测量具有一些相对于三角测量的优势，EDM测距快速、准确、经济，而三角测量所需的角度测量则相对困难和昂贵）
For some precise projects, the combination of triangulation and trilateration which is called triangulateration is applied.（在一些精密工程当中，三角测量和三边测量联合使用，被称为边角测量）
Traversing（导线测量）
A survey traverse is a sequence of lengths and directions of lines between points on the earth, obtained by or from field angle and distance measurements and used in determining positions of the point.（导线是一系列地球上点之间的有长度和方向的直线，由野外角度和距离测量获得，用来确定点位）
The angles are measured using transits, theodolites, or total stations, whereas the distances can be measured using steel tapes or EDM instruments.（角度可以使用经纬仪或全站仪来测，而距离可以使用卷尺或EDM来测）
A survey traverse may determine the relative positions of the points that if connects in series, and if tied to control stations based on some coordinate system, the positions may be referred to that system.（导线可以用来确定互相连接点的相对位置，如果想控制某些坐标系中的站点，其位置应参考该坐标系）
From these computed relative positions, additional data can be measured for layout of new features, such as buildings and roads.（从这些计算出的相对位置，另外的数据可以量出来，用以放样新的地物，如：建筑物和道路。

）
Since the advent of EDM equipment, traversing has emerged as the most popular method to establish control networks such as basic area control, mapping, control of hydrographic surveys and construction projects.（自从EDM的出现，导线测量作为最常用的建立控制网的方法显现出来，例如基础区域控制、图根控制、水道测量控制和建筑工程控制
In engineering surveying, it is ideal way to surveys and dimensional control of route-type projects such as highway, railroad, and pipeline construction. （在工程测量当中，导线测量是线型工程测量和立体控制的理想方法，线型工程例如公路、铁路、和管线建筑）
In general, a traverse is always classified as either an open traverse or a closed traverse.（总体上，导线总是分为支导线和闭路导线【按说open traverse是支导线，closed traverse是闭合导线，而connecting traverse是附合导线】）
An open traverse originates either at a point of known horizontal position with respect to a horizontal datum or at an assumed horizontal position, and terminates at a station whose relative position is not previously known.（支导线起始于一个水平位置已知（相对于一个水平基准或水平位置假定的点，终止于相对位置事先未知的站点。

）The open traverse provides no check against mistakes and large errors for its termination at an unknown horizontal position and lack of geometric closure.（由于其终点位置未知并且缺乏图形闭合，支导线不能提供对错误和较大误差的检核）This lack of geometric closure means that there is no geometric verification possible with respect to the actual positioning of the traverse stations.（这种图形闭合的缺少
意味着没有几何上的检核可能性，对于实际的导线点的确定。

【对于实际导线点的测量来说，这种图形闭合的缺少意味着没有几何检核条件】）
Thus, the measuring technique must be refined to provide for field verification.（因而，这种测量技术应当提供野外的检核使之精确。

）At a minimum, distances are measured twice and angles are doubled.（至少，距离测两遍，角度测两个测回。

）Open traverses are often used for preliminary survey for a road or railroad.（支导线经常用于道路或铁路的初测）
A closed traverse can be described in any one of the following two ways:（闭路导线可以由下面两种方式的任一种描述：）
⑴A closed loop traverse, as the name implies, forms a continuous loop, enclosing an area.
（闭合环路导线，正如名字所示，呈一个连续的环，围绕一个区域）
This type of closed traverse starts at assumed horizontal position or at a known horizontal position with respect to a horizontal datum and ends at the same point.（这种闭路导线起始于一个平面位置假设或相对于一个水平基准已知的点，并终止于该点）
⑵A connecting traverse starts and ends at separate points, whose relative positions have been determined by a survey of equal or higher order accuracy.（附合导线起始和终止于不同的点，它们由等于或高于规定精度的测量测设）
A known horizontal position is defined by its geographic latitude and longitude, or by its X and Y coordinates on a grid system.（一个已知的水平位置是由它的大地经纬度或格网系的X Y坐标表示）
Closed traverses, whether they return to the starting point or not, provide checks on the measured angles and distances.（闭合导线，无论它们是否回到起始点，都能提供角度和距离检核。

）
In both cases, the angles can be closed geometrically, and the position closure can be determined mathematically.（在两种情况中，角度可以在几何上闭合，位置闭合可以数学的确定）
Therefore they are more desirable and used extensively in control, construction, property, and topographic surveys. （因此它们更理想，在控制测量、建筑测量、房地产测量和地形测量使用更广泛）
Unit 6 Methods of Elevation Determination（高程测量方法）25页
7. GPS survey elevations are referenced to the ellipsoid but can be corrected to the datum if a sufficient number of points with datum elevations are located in the region surveyed.（GPS高程测量，它的参考面是地球椭球面，但是如果在测区有充分的高程点，可以修正至高程基准上来）
Standard deviations in elevation differences of 0.053 to 0.094 m are possible under these conditions.（在这种情况下，其高差的标准差能够达到0.053到0.094米。

）Spirit leveling （水准测量）
The most precise method of determining elevations and most commonly use method is direct leveling or spirit leveling which means measuring the vertical distance directly.（精度最高、使用最普遍的高程测量方法就是直接测垂直距离的水准测量方法）Differential leveling is used to determine differences in elevation between
points that are remote from each other by using a surveyor’s level together with a graduated measuring rod.（微差水准测量是利用测量者的水准仪和有刻度的尺来测定远距离的相隔点的高差）For example, to determine the elevations of desired point B with respect to a point of known elevation A (see Figure 1), the elevation of which (BM) is known to be above sea level, the level is set up at intermediate point between A and B, and rod readings are taken at both locations as a and b respectively.（例如，确定欲测关于点A的点B的高程，（如图1），A点的高程已知（BM点），在A和B点之间的中点处安置水准尺，分别以a和b代表在这两处水准尺上的读数）
Then the elevation of the line of sight of the instrument (being horizontal) is k nown to be the line of sight of the instrument HA + a.（那么，仪器（整平后）的视线高程就是：HA + a）【怀疑这句话不对the line of sight of the instrument多余了】
The elevation of point B can be determined by equation（B点的高程可以由方程来确定）
HB=HA + a －b
In addition to determining the elevation of point B, the elevations of any other points, lower than the line of sight and visible from the level, can be determined in a similar manner.（除确定B点的高程之外，其它点的高程，低于视线和水准仪可以看见的点，都可以以相似的方法得到。

）
But some terms should be mentioned from above.（但是上面的一些术语需要提一下）
a is called Backsight (BS) which is a rod reading taken on a point of known elevation in order to establish the elevation of the instrument line of sight.（a 被称为Backsight，是一个放在已知高程点上的尺的读数，用来求得仪器视线的高程。

）
b is called Foresight (FS) which is a rod reading taken on a turning point, benchmark, or temporary benchmark in order to determine its elevation.（b 被称为Foresight，是一个放在转点、水准点、或者是临时水准点之上的尺的读数，用来确定该点的高程）
HA + a refers to the Height of Instrument (HI) which is the elevation of the line of sight through the level.（HA + a 指的是仪器高度（HI），是过水准仪的视线的高程）
Owing to refraction, actually the line of sight is slightly curved, the effects of curvature and refraction for the horizontal distance can be reduced to a negligible amount and no correction for curvature and refraction is necessary if backsight and foresight distances are balanced in practical operation.（由于大气折光的缘故，实际上视线是有些弯曲的，曲率和折光的影响可以被当作可忽略的值，不必加入球气改正，如果在实际工作中后视距和前视距是相等的）
Trigonometric Leveling（三角高程测量）
Trigonometric leveling is used where difficult terrain, such as mountaino us areas, precludes the use of conventional differential leveling.（三角高程测量适用于困难地形，例如在山区，不能使用常规的微差水准测量。

）
Unit 8 Errors in Measurement（测量工作中的误差）32页
Measurements are defined as observations made to determine unknown quantities.（测量被定义为确定未知量的观测）They may be classified as either direct or indirect.（它们可以被分为直接观测和间接观测）A direct measurement is one where the reading observed represents the quantity measured, without a need to add, take averages or use geometric formulas to compute the value desired.（直接观测就是观测读数即代表了测量量，不需要另外加、取平均或利用几何公式来计算出所需值。

）Determining the distance between two points by making a direct measurement using a graduated tape is an example of direct measurement.（用一把刻度尺直接确定两点之间的距离，就是一个直接观测的例子）An indirect measurement requires calculation and can be determined from its mathematical relationship to direct measurements when it is not possible or practical to make direct measurements.（间接观测需要计算，当直接观测是不可能或不实际时，可以利用它与直接观测量之间的数学关系来确定。

）For example, station coordinates can be mathematically computed by measuring angles and lengths of lines between points directly.（例如，测点坐标可以由直接测得的点之间直线的角度和长度来计算）Therefore the indirect measurements (computed station coordinates) contain errors that were present in the original direct observations and propagated (distributed) by the computational process.（因此，这个间接测量值（计算出的测点坐标）包含了初始直接观测出现的和由计算过程传播（散播的）的误差。

）This distribution of errors is known as error propagation.（这种误差的散播被认为误差传播）Also, it is the indirect nature of measurements that forces the need to often apply some rather sophisticated mathematical procedures to analysis of errors and thus determine a “best value”to represent the size of the quantity.（同样，间接测量的特性需要经常应用一些更复杂的数学方法来分析误差并从而确定“最佳值”来代替测量值的大小）It can be stated unconditionally that all measurements, no matter how carefully executed, will contain error, and so the true value of a measurement is never known, and the exact sizes of the errors present are always unknown.（可以绝对地说，所有测量工作，无论多么仔细的实行，也会包含误差，因此测量的真值是永远不知道的，出现的确切的误差大小也永远不知道）Even with the most sophisticated equipment, a measurement is only an estimate of the true size of a quantity.（即使使用最复杂精密的装置，测量值也仅仅是一个量的真值的估计）This is because the instruments, as well as the people using them are imperfect, because the environment in which the instruments and people operate influences the process, and because the behavior of people, instruments, and the environment cannot be fully predicted.（这是因为同使用它们的人一样，仪器是不完美的，因为仪器和人的操作环境影响观测过程，因为人的行为，仪器，和环境不能完全预知）
However, measurements can approach their true values more closely as better equipment is developed, environmental conditions improve and observer ability increases, but they can never be exact.（然而，测量可以非常接近它们的真值，当仪器的改进，环境条件改善和观测者技术的进步时。

但是它们永远不能达到真值）By definition, an error is the difference between a measured value for any quantity and its true value.（按照定义，误差是某一量的测量值和它的真值之间的差值。

）The sources of errors fall into three broad categories which are described as follows:。