多年来，航道工程图的野外测量一直沿用平板仪作业方法。这种方法野外时间长、工作量大、精度低、成本高，对工程进度、工程质量以及经济效益等都有不同程度的影响。目前，数字化测图已广泛应用于各个测绘领域，我省航道系统也在逐步推广使用。它具有精度高、时间短、操作简便易学等优点，简化了传统的作业方法，大大缩短了作业时间，减少了野外劳动强度，对于提高作业速度和成果精度具有广泛的应用前景。其高度灵活、自动化程度高等优点，是传统的作业方法无法比拟的。
1997年，我站在淮沭新河口门疏浚工程中，在野外采用数字化测图的方法测绘该工程的工程图，收到了十分明显的效果。
1 方法和步骤
(1)根据需要首先在测区内布设导线点或控制点，当测图比例为1∶1000时，按规范规定，导线点、控制点的个数每km2不少于40个，每幅图50×50cm不少于10个。用全站仪(无全站仪也可用2″级经纬仪，3030型红外测距仪配合使用)，分别测出各导线点所需水平角、垂直角、斜距，量取仪器高、觇标高，按规范要求进行闭合。
(2)在导线点(控制点)上架设仪器，用同样方法测出所需各地物点、高程注记点、碎部点的角度和距离。
(3)实地绘出草图，标注导线点、断面点、图根点以及地物地貌、特征点的相关位置和主要特征。
(4)内业计算，将野外测得的已知数据(角度、距离)输入计算器或微机，对导线点进行平差改正(方位角闭合差、边长闭合差、高程闭合差必须满足《内河航道测量规范》的要求方可进行平差)，分别求出各导线点的平面位置和高程。
(5)用极坐标法求出各控制点、地物点、特征点等所需点位的坐标和高程。
(6)将计算出的平面位置用展点器精确地展绘到聚脂薄膜上。
(7)参照草图绘出一底图。
(8)通过一底图到实地检核，防止遗漏，确保准确、逼真。
(9)清绘晒蓝(印刷)。
其方法和步骤的流程图见图1。
2 两种测图方法的精度比较
野外大比例尺数字化测图的全过程几乎都是用解析法进行的。虽然最后成果仍表现为图解的线划图，但与传统的平板仪测图相比，有着本质的差别。数字化测图不仅在效率上有很大提高，而且大大减轻了野外的劳动强度，更为突出的是地形图数学精度的提高。现对平板仪测图与野外数字化测图测站点、地物点的平面位置及高程精度进行分析比较。
2.1 平板仪测图
(1)以1∶1000比例尺为例，平板仪测图地物点、测站点的平面位置主要取决于测站、视距、描绘方向、刺点等方面的误差来源：
①测站点误差：±0.18mm；
②视距误差：±0.2mm；
③描绘方向误差：±0.1mm；
④刺点误差：±0.14mm。
根据以上误差来源，按照公式计算求得地物点的平面位置中误差为±0.32mm。
(2)平板仪高程精度主要取决于测量高程时的测量误差，主要有：
①视距误差：±0.2mm(当视距为100m时)；
②垂直角观测误差：±1′；
③仪器高觇标高的量测误差：±0.01m。
在不考虑起始点高程误差的情况下，根据公式可求得各高程点的中误差为±0.04m。
2.2 数字化测图
(1)由于红外测距仪和全站仪等高精度仪器的逐步应用，使外业的所有测站点、地物点全部采用经纬仪导线方法完成。在已知等级点的控制下，只要布设两级导线即可满足测图的要求。假如各级导线都采用直线等边附合导线的形式施测，根据有关规范和实际作业中的最不利情况，按点位中误差估算公式计算出测站点的点位中误差为±0.03mm。
(2)地物点的平面位置野外测量方法有极坐标法、导线法、对称点法，而在实际工作中采用极坐标法测设地物点比较方便，一般是将经纬仪(全站仪)设置于测站点A上，对置于地物点上的楼镜进行水平角和距离的测定，如图2所示。
水平角观测一测回，故其测角中误差为5″，而测距误差由于棱镜比中杆的半径约大2cm左右，故使对中杆靠紧垂直地物点(房角、电杆等)位置的误差一般可达1.5～2cm，若考虑其他测距误差，则可取0.02m。以边长100m计算，根据计算公式可得出地物点的平面位置中误差为±0.02mm。
(3)高程点的测定和地物点的测定方法完全一样，垂直角只观测半测回。以距离100m为例，根据公式求出高程站点、地物点的高程测量中误差为±0.02m，按规范要求1∶1000测图时，高程注记点的中误差一般地原为±0.05m。另外，等高线(等深线)的高程精度，实际是数字高程横型插求点的高程中误差。一般认为影响数字高程模型主要因素有：地形类别、内插方法、采样点密度和采样方法、粗差剔除程度等4个方面。通过试验，其等高线精度通常可以达到±0.3～±0.4m，可以满足1∶1000测图时的高程精度，即满足1/2～1/3基本等高距的要求。
野外数字化测图，最好采用增加高程注记点和缩短断面间距的办法，以提高整个图幅的高程精度，所需高程点可通过高程注记点和断面点内插求得。等高线(等深线)精度对工程质量、土方计算、工程预算有直接关系，务必慎重。综上所述，野外采取数字化测图的高程精度比规范规定有较大幅度的提高。
两种测图精度的分析结果见表。
项目 比例尺 测站点平面位置精度 (图上mm) 高程精度(m)
测图方法
平板仪测图 1：1000 ±0.5 ±0.4 ±0.04
数字化测图 1：1000 ±0.03 ±0.02 ±0.02
3 几点体会
经过对平板仪测图和数字化测图的精度比较，可以看出野外数字化测图具有以下优点：
(1)成图精度高：野外数字化测图比传统的平板仪测图，在平面、高程精度方面提高的幅度较大，其中测站点平面位置提高16倍，地物点提高20倍，高程精度提高50％，这对地图的使用具有重要价值，对航道工程测量同样有不可估量的作用。
(2)减少野外工程量，提高工作效率。过去使用平板仪测图需仪器设备多，而且笨重、操作繁琐，每台平板仪需6～7人配合才能工作。而野外采用数字化测图采用高精度仪器，虽然全站仪在航道系统尚不普及，但目前普遍使用的J2经纬仪和常州产的3030型红外测距仪精度高、体积小、重量轻、操作方便、速度快，仅3～4人就可工作。过去每逢夏季阴雨天就要停工，现在因外业时间少，利用雨停的间隙或短时间速战速决便可完成工作。笔者经过调查，平板仪1∶1000比例尺测图时，以苏北平坦地区(一般地区)为例，每km2需30～40d/台才能完成，需资金1.4万元。野外采用数字化测图每km2仅需20～30d/台就可完成，只需资金0.5万元左右；同时把大量的野外工作转移到室内来，野外工作量减少了1/3，每km2可节约资金近万元。不仅降低了劳动强度，而且提高了工作效率，减少了成本，为提前完成工期打下了基础、赢得了时间。
(3)可任意制作不同比例尺地图。平板仪测图是根据比例尺在实地一次性完成，如比例尺不同则需野外重测；而野外数字化测图是利用野外采集的已知数据，由内业计算出各点的平面位置和高程，适合各种比例尺的需要。如比例尺更换，仅在室内重新展点绘制即可，无需野外重测，避免了重复劳动，缩短了成图周期。
(4)容易保存。我省航道系统微机已基本普及，野外采集的数据和计算成果，由内业编好程序输入微机，随时调用，便于档案管理，还可为建立数据库打下基础，不再保存原始手薄和用地图存档，一旦需要随时从微机中把数据调出，制版晒蓝即可。
4 结束语
野外大比例尺数字化测图对航道管理、养护、航道工程是最有效的手段，它不仅精度高、成图周期短，而且大大提高了工作效率和经济效益。数字化测图必将取代传统的测绘方式，为我省的航道建设提供更优质的服务。
Over the years, waterway engineering drawings of field measurements has been in use flat-panel instrument practices. This method field a long time, heavy workload, low precision and high cost of the projects progress, project quality and value for money and others have varying degrees of impact. At present, the digital mapping has been widely used in surveying and mapping in various areas of our province are gradually promoting the use of routing systems. It has high precision, short time to learn the advantages of easy operation, simplifying the traditional practices, greatly reducing the operating time and reduce labor intensity of the field for improving the operation speed and accuracy of the results has broad application prospects. Its highly flexible, high degree of automation, the advantages of the traditional practices can not be compared.
In 1997, I stood in the door Huai Shu New River dredging project, in the wild use of digital mapping method of mapping the project's engineering drawings, received a very significant results.
1 methods and steps for
(1) According to the need to first measure the area planted in the wire points or control points, when the ratio of 1:1000 mapping, when, according to specification, wire points, the number of control points per km 2 less than 40, each piece of Figure 50 × 50cm less than 10. With the total station (no total station can also be used 2 "level theodolite, 3030 with the use of infrared range finder), respectively measure the horizontal angle required for the Traverse, vertical angle, slant range, the amount of equipment to take high-spy elevation, according to standard closing requirements.
(2) wire point (control point) at erecting equipment, measured the same way around the materials needed to point, elevation Note points, broken angles and distances, the Ministry of points.
(3) Field Draw sketches, mark wire points, cross-section point, figure the root points, and surface features landscapes, feature points related to the location and main features.
(4) within the industry in terms of the known field measured data (angle, distance), enter the calculator or computer, right Traverse Adjustment for correction (azimuth closed poor, poor side length closure, elevation difference closure must be met " Inland Waterway measurement standard "requirements before proceeding with adjustment), respectively, find the wire points, the location and elevation plane.
(5) with the polar coordinate method calculate the control points, the feature points, feature points needed for point and the coordinates and elevation.
(6) to calculate the location of the plane-point devices with the show accurately plotting to polyester film.
(7) With reference to the draft plan Draw a base map.
(8) through a base map to the field check, to prevent the omission, to ensure accurate and realistic.
(9) and Qing painting drying blue (printing).
Its methods and procedures of the flow chart shown in Figure 1.
2 are two methods of Accuracy of Mapping
Large-scale Digital Field Mapping of the whole process almost always carried out with the analytical method. While the final outcome is still marked by the line graph diagrams, but the traditional plane table mapping, compared with the essence of the difference. Digital Mapping not only in efficiency has greatly improved, but also greatly reduced the labor intensity of the wild, more prominent is the mathematical accuracy of topographic maps improved. Are pairs of plane table mapping of digital mapping and field test site, the feature point location and height accuracy of planar analysis and comparison.
2.1 The plane table mapping
(1) to 1:1000 scale, for example, plane table mapping surface features points, measuring location of the site depends largely on the plane station, line of sight, depicts the direction of barbed-point source of error in such areas as:
① Measuring site error: ± 0.18mm;
② sight error: ± 0.2mm;
③ depicts the direction of error: ± 0.1mm;
④ barbed point error: ± 0.14mm.
Based on the above error sources, in accordance with formula obtained point features in the plane location error of ± 0.32mm.
(2) The plane-elevation accuracy is determined by measurement error when measuring height, mainly:
① sight error: ± 0.2mm (when the line of sight for the 100m time);
② vertical angle observation error: ± 1 ';
③ high spy apparatus elevation measurement error: ± 0.01m.
Without taking into account the starting point elevation error cases, the formula can be obtained in each elevation point margin of error of ± 0.04m.
2.2 Digital Mapping
(1) Because infrared range finder, and total station instruments such as the gradual application of high precision, so that outside the industry, all measurement sites, the feature points used in all theodolite wire method to complete. Known under the control of grade point, as long as two wires can be laid to meet the mapping requirements. If the wire at all levels have adopted straight equilateral Traverse in the form of Shi measurement, according to the norms and the actual operations of the most adverse circumstances, in accordance with point and error estimation based on a formula measuring site of the point position in the margin of error of ± 0.03mm.
(2) features in planar point location of field measurement methods are polar coordinates method, wire method, symmetry point method, but in practice the use of survey and design features in polar coordinates method more convenient point, the general is the theodolite (total station) installed at the test site A, the pairs of points placed on the floor surface features mirror for horizontal angle and distance measurement as shown in Figure 2.
Horizontal angle measurements observed a return, so the angle measurement error of 5 ", while the ranging error due to the prism pole than in the radius of about 2cm or so big, so try to be so that the vertical surface features of the pole point (angle, pole , etc.) the location error is up to 1.5 ~ 2cm, if take into account other ranging error, then the desirability of 0.02m. in order to calculate a side length of 100m, according to the formula can be derived features in planar point location error of ± 0.02mm.
(3) the determination of elevation points, and the feature point determination method exactly the same, only the observation and a half vertical angle measurements back. To distance 100m, for example, according to the formula derived elevation sites, the feature points of the height measurement error of ± 0.02m, according to specifications 1:1000 mapping, the elevation point of note on the error generally formerly ± 0.05m . In addition, contour (isobath) and elevation accuracy, the actual digital elevation cross-type plug of the elevation of point of error. Is generally believed that the main factors affecting digital elevation model are: terrain type, interpolation methods, sampling point density and sampling methods, excluding gross errors in the degree of four areas. Through testing, the accuracy of contour lines can often be achieved ± 0.3 ~ ± 0.4m, to meet the 1:1000 mapping accuracy of the time of elevation, that is, to meet the 1 / 2 ~ 1 / 3 of the basic high-distance requirements.
Field Digital Mapping, preferably by increasing elevation point and the note on ways to shorten the distance between sections in order to improve the height accuracy of the entire map sheet, the required elevation point by point and the cross-section elevation Note interpolation points obtained. Contour line (contour line) accuracy of the engineering quality, earthwork calculations, project budget is directly related to caution. In summary, field measurements taken by the digital elevation map more accurate than standard provides for a more substantial increase.
two kinds of mapping accuracy of the analysis results in Table.
Item scale measuring site plane position accuracy (map mm) Height Accuracy (m)
Mapping Method
Plane table mapping 1:1000 ± 0.5 ± 0.4 ± 0.04
Digital Mapping 1:1000 ± 0.03 ± 0.02 ± 0.02
3 Some Experience
After a plane table mapping and digital mapping accuracy comparison, we can see the field of digital mapping has the following advantages:
(1) into a map with high precision: the field of digital mapping instrument than the traditional flat-panel mapping, in the plane, elevation precision improved by a big margin, which measured sites increased 16-fold flat position, the feature points, increased by 20 times, elevation Accuracy increased by 50%, which is of great value to the use of maps, engineering survey of the channel also has an invaluable role.
(2) to reduce the amount of field work, improve work efficiency. Over the past using the plane table surveying and mapping equipment required are numerous and heavy, cumbersome operation, each plane-take 6 ~ 7 people to work with. The field use of digital mapping using high-precision instruments, although the total stations in the channel system is not universal, but widespread use of the J2 theodolite and Changzhou-based infrared range finder 3030 produced high accuracy, small size, light weight, operation convenient, fast, only 3 to 4 people can work. During the summer rainy days to go before the last lockout, and now has little time for outside the industry, using the rain stopped a short time gap, or a quick fix can be done. I After an investigation, plane table 1:1000 scale mapping, use a flat area in northern Jiangsu (general area) as an example, for every km 2 take 30 ~ 40d / units to complete, the need to fund 14 thousand yuan. Field use of digital surveying and mapping for every km 2 only 20 ~ 30d / units can be completed, only about 05,000 yuan of funds; the same time a lot of field work transferred to the interior, the field reduced workload 1 / 3 per km 2 can save money almost million. Not only reduces the labor intensity, but also improve work efficiency, reduce costs, in order to lay the foundation for early completion time, winning time.
(3) can be arbitrarily create maps on different scales. Plane table mapping is based on the completion of a one-time-scale in the field, such as the scale of different Zexu field re-test; and field is the use of digital mapping data collected in the field known from within the industry point of the plane were calculated for each location and elevation, suitable for all kinds of scale needs. Such as scale change, only in the indoor exhibition points to re-draw can be, without field re-test, avoiding duplication of effort and shortening into the map cycle.
(4) easy to save. Waterway system in our province has been basically universal computer, field collected data and calculation results, compiled from within the industry enter the computer a good program at any time call, easy file management, but also lay the foundation for the establishment of a database is no longer preserve the original hand-thin and use maps archive If necessary, the data transfer from a microcomputers out blue plate can be drying.
4 Conclusion
Large-scale Digital Field Mapping pairs of channel management, conservation, waterway engineering is the most effective means of not only high precision mapping cycle is short, but also greatly enhance the working efficiency and economic benefits. Digital Mapping mapping will replace the traditional manner, the channel construction of our province to provide better service.
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