unit 3

Unit3 Distance Measurement第三单元距离测量第一段对距离测量进行概述。

后面从所采用的仪器设备方面，讲述了4种量距方式，分别是……，并对每种方式的原理、精度进行阐述。

One of the fundamentals of surveying is the need to measure distance.测量的一项基本工作就是距离测量。

Distances are not necessarily linear, especially if they occur on the spherical earth.距离不一定必须是直线，尤其在测量球面距离时。

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.这里提到的距离测量基于欧几里得空间，即可将两点间的距离视为直线距离。

Distance between two points can be horizontal, slope, or vertical.两点间距离可以是水平的、倾斜的或者垂直的。

Horizontal and slope distances can be measured with lots of techniques of measurement depending on the desired quality of the result.根据所要得到的数据要求，两点间的水平距离或倾斜距离可用许多种设备测量得到。

In plane surveying, the distance between two points means the horizontal distance.在平面测量中，两点间的距离指的是水平距离。

If the points are at different elevations, then the distance is the horizontal length between plumb lines at the points.如果两点位于不同高度上，两点间的距离就是过两点的铅垂线间的水平距离。

Here gives a brief summary of relevant techniques and their respective accuracies:这里对距离测量所用的技术及其精度做一个总结：Pacing and Odometer步测和里程表Pacing is a very useful form of measurement though it is not precise, especially when surveyors are looking for survey marks in the field.尽管步测精度不高，但却是一种非常有用的量距方式，特别是在测量员在野外寻找测量标志的时候。

performed on horizontal land, while the accuracy of pacing can’t be relied upon when pacing up or down steep hills. 在平地上使用步测量距时，精度可达到1/100 ～1/ 500，然而在斜坡上，步测的精度却不可靠。

The odometer is a simple device that can be attached to any vehicle and directly registers the number of revolutions of a wheel.里程表是一种可固定在任何车辆上的小装置，它可直接记录下车轮的转数。

With the circumference of the wheel known, the relation between revolutions and distance is fixed.车轮的周长已知，转数和距离的关系便是固定的。

Ordinary Taping and Precise Taping普通卷尺和精密卷尺Taping is a very common technique for measuring horizontal distance between two points.卷尺是测量两点间水平距离时应用很普遍的一种仪器。

Ordinary taping refers to the very common tapes that we can buy them in stores, such as the plastic tapes or poly tapes.普通卷尺指的是我们能在商店买到的那种卷尺，比如塑料卷尺和聚酯卷尺。

Such tapes have low precision in distance measurements with about 1/ 3000 ～1/ 5000.这种卷尺精度较低，大概在1/ 3000 ～1/ 5000。

The precise taping refers to the steel tapes and which are much m ore expensive than the plastic tape and have higherprecision of 1/ 10000 ～1/ 30000.精密钢尺指的是钢尺，与塑料钢尺相比，它的价钱较高并且具有较高的精度，大概在1/ 10000 ～1/ 30000。

Invar tapes are composed of 35% nickel and 65% steel.因瓦钢尺是由35%的镍和65%的钢制成的。

This alloy has a very low coefficient of thermal expansion, making the tapes useful in precise distance measurement. 这种合金具有很低的热膨胀系数，在距离测量中非常有用。

Many tapes are now graduated with foot units on one side and metric units on the reverse side.现在，许多钢尺都是一面是英尺单位注记另一面是米制单位注记。

Metric units are in meters, centimeter and minimeter with the total length of 20 m , 30 m , 50 m and 100 m.米制单位的钢尺刻画有米、厘米和毫米，并且总长度有20m、30m、50m和100m若干种类型。

If we want to measure the horizontal distance between the two points A and B, we can do like this:如果我们想测量A、B两点间的水平距离，我们可以这样做:With zero of the tape to the higher point B and tape going along the point A, we can measure the horizontal distance by using the plumb bob with pump line entering to the point A.将卷尺的零刻度线对准地势较高的B点，然后沿着AB直线的方向将卷尺拉向A点，可以通过一个对准A点的铅锥所确定的铅垂线来测量AB两点间的水平距离。

To judge the exact horizontal line, we should move the tape up and down along the pump line and we will find the changes of reading in the tape.沿着铅垂线上下移动卷尺，通过观察读数的变化，从而精确的得到AB两点间的水平线。

The shortest reading of the tape is the horizontal distance.卷尺上的最小读数就是水平距离。

If the distance is longer than the length of tape, then we can divide the long distance into several segments and get the total distance by plus each segment together.如果AB两点距离大于卷尺长度，可以将总距离划分为几个小段，再将各小段读数相加即可得到总长度。

Since different tapes have different starts of zero of the tapes, it is very important to judge where the zero of the tape begins.由于不同钢尺有不同的零刻度线，所以明确刻度线的位置是非常重要的。

Tacheometry and Stadia视距测量和视距仪Tacheometry is an optical solution to the measurement of distance.视距测量是距离测量中的一种光学解决方案。

The word is derived from the Greek Tacns, meaning“swift”, and metrot, meaning“a measure”.这一词汇起源于希腊语tacns，意思是“迅速的”，和metrot（同样是希腊语）意思是“方法”。

Tacheometry involves the measurement of a related distance parameter either by means of a fixed-angle intercept.视距测量包括一个相关距离参数的测量和与定角截距（尺间隔）相关的测量。

Theodolite tacheometry is an example of stadia system.经纬仪视距测量就是视距测量的一个例子。

The theodolite is directed at the level staff where the staff is held vertically and the line of sight of the telescope is horizontal.将经纬仪望远镜瞄准水准尺，使水准尺竖直，望远镜视线水平By reading the top and bottom stadia hairs on the telescope view and then the horizontal distance from center of instrument to rod can be obtained by multiplying the stadia interval factor K by the stadia interval and plus the distance C which is from the center of instrument to principal focus, i .e. D = Ks + C.在望远镜视野里读出视距丝的上下丝读数，则仪器到水准尺的平距可由视常数K（the stadia interval factor）乘尺间隔，再加上从仪器中心到主焦点（principal focus）的距离C得到，也就是D = Ks + C。