公路定线的概念：
在选线布局阶段选定的“路线带”（或叫定线走廊）的范围内，按已定的技术标准，结合细部地形、地质等自然条件，综合考虑平、纵、横三面的合理安排，定出道路中线的确切位置的过程。 公路定线的基本原则：
车行道要素如弯道和坡道必须互相组合，在满足设计规范和安全标准的要求的同时，提供满足设计通行能力并且平稳的交通流体系。
对现有资料的室内研究：
定义：
该阶段是对要修建公路地区获取的数据进行检测，相比其他领域或者摄影测量调查，通常优先室内研究调查。获取的一切数据都要被收集和检测。
数据来源：现有的工程报告、地图、航摄照片和图表，而这些又来自于国家的交通运输、农业、地质学、水文学以及矿业等部门。 数据类型
数据初步分析：
选择的具体地址是否因为对所选地区的经济、环境、社会等因素的进一步考虑而被排除。（例如，如果发现一个重要的历史古迹和建筑位于路线可能通过的区域，则应立即确定通过那个区域的任何路线下一步将不被考虑。）该阶段完成之际，工程师就能选择公路横过的大致范围。
Definition:The first phase is the examination of all available data of the area in which the road is to be constructed.It’s uaually carried out in the office prior to any field or photogrammetric investigation.All the available data are collected and examined.
Sources:These data can be obtained from ’s Types:
Preliminary analysis:It will indicate whether any of the specific sites considered for poible route location, it maybe immediately decided that any route that traverses that site should be excluded from further consideration.) At the completion of this phase, the engineer will be able to select general areas through which the highway can traverse.
Reconnaiance survey（踏勘测量） The object of this phase is to identify several feasible routes,each within a
band of a limited width of a few hundred feet.(目的是为了确定可行性路线）——————可行性路线的确定方法如下：
Feasible routes are identified by a stereoscopic examination of the aerial photographs.(可行性路线通过航拍图来确定）——以下是需要注意的：
The factors should be taken into consideration（确定航拍图需要考虑的因素）such as:
Terrain and soil conditions;
Serviceability of route to induatrial and poppulation
areas ；
Croosing of other transportation facilities: rivers,etc.
Directne of route.
Control points between the two endpoints are determined for each
feasible route.（可行性路线又决定了控制点——看图控制点的测量）——举例：桥址（图片）
Preliminary location survey（初步定线）
The position of the feasible routes are set as closely as poible by Establishing all the control points and determining preliminary vertical and horizontal alignments.（初步定线是通过确定控制点跟初步的纵面跟平面线形）——如图所示线形
Preliminary alignments are used to evaluate the economic and environmental feasibility of the alternative routes.（初步的线形是为了估计经济跟环境的可行性）——需要注意的是：经济跟环境可行性的考虑办法，如下
economic feasibility:benefit-cost ratio（效益成本化）
factors: road user costs, construction costs, maintance costs, road user benefits and any diabenefits（效益成本化需要考虑的因素）
environmental feasibility:the impact on surroundings（环境可行性——建路对于环境的影响）——最后看图：当可行性达到一定的效果之后可以实现经济、环境的共利。
The final location survey is the detailed layout of the selected route.The horizontal and vertical alignments are determined and the positions of structures and drainage channels are located.
Splines and curve templates are available that can be used in this proce.
定测就是对所选路线的详细布局。 在这个过程中，纵面线形和平面线形得到规划，公路结构和排水渠的位置也得到确立。
可以用曲线尺和曲线板来定线。
Construction of highway at any location will have a significant impact on local environment.This environment includes plant, animal human communities and encompaes social, physical, natural and man-made variables.The construction of highway at a given place may result in significant changes in one or more variables, which in turn may offset the balance and result in significant adverse effects on the environment.This may lead to a reduction of the equality of the animal and/or human communities.
Construction of highway may also bring great benefits to local economy.The highway may effectively reduce logistics cost of local place and improve the efficiency of economic operation.
Freeways brought convenience to exchange between cities, which will strengthen the link between the areas, thus the regional advantage is strengthened.Therefore, the investment promotion will be more attractive to improve the investment environment.Highway will also contribute to the economic development.
无论公路建在哪里，它都对当地环境产生重大影响。这个环境包括植物，动物人类群体以及社会的，物理的，自然的和人为的变量。特定区域的公路的建设可能会引起一到多个变量的重大改变，这些改变将会打破平衡并对环境产生极大的不利影响。这将会导致动物和人类群体的不平衡。
建设公路也会给当地经济带来巨大效益。它可以有效地降低沿线地区企业物流成本，提高经济运营的效率。公路为城市间的往来带来了方便，加强了地区之间的联系，使区域优势得到加强，在招商引资上更具有吸引力，改善了投资环境。公路的建设同时也能对农业的发展起到推动作用。
The methods to locate highway can be divided three parts:
Paper location refers that the engineer locate the rough path through the paper.
Site location means that the engineer surveys soil texture、terrain and so on on the spot.
Aerial survey location analyse the selected highway by the aerial photographs.
公路定线的方式一般有以下三种：
纸上定线指的是在地形图上定出道路中线的工作。
现场定线，指的是道路修建工程师到修路现场进行勘测，对土质、地形等方面的工作做现场调查。
航测定线，利用卫星定位，在空中拍摄航拍图来对所要规划的公路进行分析
