1. Preface

As electronic total station and the popularization of computer, topographical map mapping methods are being gradually switching from a traditional white law mapping to digital mapping direction. Especially in the eastern coastal developed areas in China, digital mapping is almost occupied most of the topographic map mapping market. I have engaged in digital mapping work for nearly four years, following on the digital mapping of several aspects of talk about some personal experience, but there are things that set and the fallacious 10000 hope you teachers, experts and peers will not hesitate to enlighten.

二. Practices

At present in China, access to digital maps There are three main methods: Original digital, aerial digital mapping, terrestrial digital mapping. Regardless of which approach, whose main operations are a three-step process: data acquisition, data processing and topographic map data output (print drawings, provide a floppy disk, etc.).

1. Original Digital

When a city (region) need to use digital terrain map and a time because of financial difficulties, or subject to time constraints and other reasons, the method is further suitable for economical. It can fully utilize existing topography of the map, only equipped with computers, digitizers, plotters Coupled with a digital software, you can work and can be obtained within a very short time the number of results. 1:00 Even if funding for the purchase of equipment is also difficult to implement, but also bring a drawing with digital capacity to act on behalf of the mapping unit. Its work in two ways: hand on the track and scan vector-based digital post-digital, of which the latter than the former kind of high precision and high efficiency.

However, obtained using this method due to its accuracy Original digital map accuracy, coupled with the figures produced by the process of a variety of errors, so its accuracy worse than the Original accuracy. And it reflects only the white paper into a variety of surface features on the maps of surface topography, are potential was not so good. So it only as a stopgap measure rather than the long-term strategy.

In order to make full use of the law can be a digital map, can be measured through the repair, and other methods tested additionally, part of the surface features measured the precise coordinates of points, and then the coordinates of these points instead of the original coordinates, by adjusting can be increased to some extent the accuracy of the original plan. With constantly updated maps, the measured coordinates of the increase in accuracy is also the map will be correspondingly improved.

2. Aerial Survey digital mapping

When an area (or measurement area) is large, you can use aerial camera images in the air intake on the ground, through the interpretation of foreign trade, including the industry to establish a ground model, through computer mapping software used in the model on the measurements, direct access to Digital topographic maps. With the surveying and mapping technology, digital photogrammetry has been an area in China has made a successful pilot in the near future, will be promoted. It is through the use of digital cameras in the air and receive a digital image of the aerial survey within the industry through a special software on the computer as digital images of the match, the establishment of terrestrial digital model, and then through a dedicated software to obtain digital map. It can be said that this will be our future digital mapping is an important direction of development.

The method is characterized by a large number of foreign business can be moved indoors to complete survey work, it has a mapping speed, high precision and uniform, low cost, from climate and seasonal restrictions and so on. It is particularly suitable for dense urban areas a large area mapping. However, a larger initial investment of the method, if a small test area, it becomes a higher cost. So now is basically to assume some of the larger units.

3. Terrestrial Digital Mapping

Meet the requirements in the absence of large-scale map of the region or the region, surveying and mapping expenses were relatively adequate, can be used directly on the ground digital mapping of the method, which is also known as internal and external business integration, digital mapping, surveying and mapping units in China are used by various Most digital mapping. Obtained using this method of digital maps is characterized by high precision, as long as certain measures to be taken, important features in the neighboring control points relative to the precision of control can be achieved within 5cm. But its cost of manpower, material and financial resources is relatively large. In this article, is mainly to talk about this experience.

三. The choice of mapping software

For a mapping unit, the digital mapping is an important issue is to choose a good fit in this unit to use mapping software. Since it is often up to this unit with a very good software, to the other units do not necessarily apply, so the choice of each unit of software issues should be a concrete analysis of specific problems, not just parroting.

Measure of a mapping software standards, first of all depends on the suitability of the software unit of the actual situation; 2 depends on its feasibility, whether friendly interface, simple and easy to learn and so on; three features depends on the availability of its suitability in this unit.

At present the mapping units used by the software, manifold, and many others. But basically into two types, one of the system (unit) self-developed, and the other is by specialized mapping software developers, but for commercial purposes available to the general users, and also compare the various mapping units used and more. In this article, it is the latter-mentioned software.

Mapping software on the market today the most used There are three: First, Tsinghua Hill-dimensional co-developed with Tsinghua University's civil engineering measuring Ba EPSW (Electronic Plane-table Surveying and Mapping system) series; Second, the Survey and Mapping, Wuhan Reid Automation of the RDMS series; three of Guangzhou with Guangzhou Southern Surveying Instruments Inc. to open thought the company's CASS series and SCS series. The following simple and make a comparative analysis.

EPSW series is mainly used for measurement and automatic drawing a variety of large-scale digital topographic maps, cadastral maps, pipeline maps, surface features floor plans, section plans, etc., but its function is different from these specialized software in the. Its main features are as follows: a real-time mapping give full play to the original mapping of the flat edge, or measure that is obvious, the obvious that is measured, in the midwifery field topographic maps, really achieve integration both within and outside the industry; 2 with multiple pieces Ministry of measurement methods; three friendly interface, easy to operate fast and easy to learn. 4 step unique measurements, you can while mapping the root, while the Ministry of test pieces and finally re-adjustment.

The software's biggest advantage is consistent with the old surveying and mapping work of the staff experience and habits, but also the job done efficiently, it should be said that China is now in the electronic flat panel Mapping System do best, therefore, well received by the surveying and mapping personnel love, but also account for most of the mapping of electronic flat-panel market. It created a new situation in the digital mapping of China's digital mapping technology, the promotion has played a great role in promoting.

However, although the software also provides graphical, such as scaling, windows, move, delete and other functions, but within the industry point of view, these functions can not satisfy the need for editing within the industry, but it had outside the industry outside the industry, the completion of the work still, it seems contrary to the digital mapping to reduce the original intention of the work outside the industry, and outside the industry to use a portable computer is easy to damage.

RDMS series graphics platform in the GIS to develop a specialized mapping software, also provides an electronic flat-panel method can also make use of electronic hand-book or a total station measurement data stored on the computer and then transmitted to interactive editing of the way into the Fig. It provides functionality that the original measurements used to basically be able to maintain a consistent, relatively easy to learn, surveyors can quickly be familiar with and get started operation, provides a cadastral survey of the relevant content, for the handling of cadastral convenient form. Therefore, many engaged in cadastral units for selection it.

For users already familiar with AUTO CAD terms, CASS series and SCS series is a good choice because they are based on the development of AUTO CAD platform, AUTO CAD all the features that it can be used, while the AUTO CAD is the world's We have identified a total of mapping platform, its editorial function is obvious to all.

CASS and the SCS features similar to their own strengths with the short. CASS services can be said to be a phone-call, while the SCS service in the recent period can not be on par with it. They offer three kinds of practices: E-flat way, Original digital methods and the integration within and outside the industry. In the CAD, based on the development of a number of features, such as the amount of fixed-point calculation, graphics, copy, drawing multi-functional composite lines. In addition, it also provides the form of cadastral mapping and drawing management functions. For which both want to use electronic flat-panel mode operations, but also in the indoor units in terms of mapping editor, you can select it.

Of course, these functions of the software as time goes on gradually improved. Understanding of the software is only my opinion one.

四. Digital Mapping outside the industry, the implementation of the work

1. Control Survey

In the digital mapping work, control the work of measurement, compared with the traditional control measure, it should be easier, of course, in the new specification, the requirements of this on the one hand there is not much change, but according to my actual

Work experience and accumulated, there are some restrictions can be relaxed, especially in Figure Root Control.

With the development of GPS technology, the popularity of mature and total stations, triangulation has now largely faded in this stage of the control measure. Therefore most of whom, no doubt, greatly reducing the intensity of work. Triangulation removed all the shackles of the restrictions, replaced by a more flexible GPS network and cable (Network) measurements. In this article, just from Topographic Surveying and Map root encryption to make a study.

Now time for the mapping units used in the precision of the electronic total station is usually 6 ", 3 +5 ppm below, together with electronic automatic readings, so it's actually much higher than its nominal accuracy of high precision, relative to the optical theodolite, the more a competitive advantage.

As we all know, in the traditional surveying and mapping in the ground plane points, the location of the impact of the error by the following error:

1. Map plotting the root point of error M Show

2. Determination of surface features from the point distance error of M

3. Determination of features in the direction of error of M barbed point M draw

4. Topographic map surface features point-point error of M stab stab

5. Qing Hui M when the error caused by painting

In conclusion, topographic maps on the location of surface features point of plane error can be expressed as

M material =

1:1000 scale with a maximum line of sight for the 100 meters, for example, based on experience, with the following table

Errors M Exhibition mm M distance mm M to mm M barbed mm M painted mm M material mm

Value 0.18 0.39 0.18 0.20 0.08 0.51

In the Digital Mapping, because the computer automatically show point, so figure the root points and features in point plotting error is negligible, as a 0. M is for the remaining distance, M to the. Take the direction of the error is three times the nominal precision limits, because it is semi-measured back angle measurement, so the direction of the error 6X 2X3 = 17 ", take pieces of the Ministry of point-to-station distance of 300m, then the M to the = 17 / 206265X300 = 0.024m, range finder to take a nominal accuracy of 3 +5 ppm. take into account the measurement of the prism is not in place, and other factors, from experience the value of 0.020m. then the plane point was measured relative to the diagram root point of error is 0.032 m.

Is clear from the line of sight a good circumstances, as opposed to total station theodolite angle measurement, distance measurement accuracy increases and computer applications, measuring the distance between the points of broken can enlarge the root point of the density map can be used for the corresponding reduction in side length can be extended to 100-300 meters. For the sub-station, two stations can also be without the restrictions, according to my practice, support 3 to 4 points can still meet the required accuracy. Of course, in the city as densely built-up areas, and pass under poor conditions, taking into account topographic map after the repair or engineering lofting measurement requirements, plans should increase the density of the root point.

2. Broken Department of Survey

Digital Mapping, and broken the Ministry of the main method for measuring polar law, had measured the coordinates of the points of the majority of pieces, may use the software in the direction of intersection, distance intersection, cross-foot measurement method or methods such as the amount of calculation to obtain fixed-point the coordinates of the remaining points, and then supplemented by the software in the offset, copy, extension and other functions, receive a final graphics.

Small mapping units, mainly tested additionally measured topographic map maintenance repair work, construction stake out, deformation observation, municipal engineering, and topographic maps and other mapping services. Because a wide range of large amount of staffing as much as possible in the brief, and it should not be taken with some large-scale surveying and mapping units, methods of operation and the need to create a set of methods suitable for this unit.

In the non-electronic flat-panel digital mapping, many of the units in the methods used for the external sector sketch + indoor interactive editing to complete the surveying and mapping work. But in that case, it is bound outside the industry will reduce the efficiency of the operation is relatively cumbersome. In the measurement of the operation, drawing sketches is not simple, particularly in the building for a long time, which was troublesome, coupled with hand sketches in terms of manpower is also a waste. I team topographic mapping group, composed basically of two people, one observation to make in the total-station records and coding, one person running feet, and graphics within the industry, after years of practice, that is feasible.

In the dot encoding, in general, can take 6-7 for the (0 to 9) (XX) (XXX), the first one to connect the relationship, such as 0 means that independent points, not with the other spots in front of contact ; a point in front of the same surface features (appearance), with the former point of connection; 2, said with a 1:00 to 1:00 with every other relationship; 3 expressed in three directions, four said that the surface features (appearance) to this end; 5 curve company; and so on, all units with their own conventions. Second to third place for the surface features (appearance) of the code, such as two-layer brick for the F2, shower enclosure for the F0, in the housing for the FJ, the wall for the WQ, reinforcement scarp as K2, is not reinforced scarp of K1 , high voltage for the D2, transmission lines for the D1, communication line D3, land type community to DL and so on. The last three automatic increases in the total station point number, as shown below:

The above encoding method is applied to the points obtained by the point number encoded as follows:

Dot dot code coding Remarks Remarks

1 0F3001 brick 3 began 15 0DL015 to class practitioners to start

2 1F3002-point connection with the previous 16 1DL016 connected with the previous point

3 1F3003 with the previous point with 17 1DL017 connected with the previous point

4 1FY004 brick terrace of three points connected with the previous 18 4DL018

5 0F2005 brick two reinforcement scarp began 19 0K1019 not start

6 1F2006-point connection with the previous point of connection with the previous 20 1K1020

7 1F2007 with the previous point with 21 3KT021 connected with the previous point, there is a rice field direction

8 0F0008 start shower enclosure 22 3KT022 connected with the previous point, there is a rice field direction

9 1F0009 with the previous point with 23 4K1023 is not the end of Consolidation scarp

10 1F0010 with the previous points, beginning with 24 0K2024 reinforcement scarp

11 0D1011 low-voltage line begins 25 3KT025 connected with the previous point, there is a rice field direction

12 1D1012-point connected with the previous 26 3KT026 connected with the previous point, there is a rice field direction

13 1D1013 with the previous point with the end of 27 4K2027 reinforcement scarp

14 1D1014 connected with the previous point

And so on, when all the points outside the industry, the completion of the number (code), the back room can be transmitted to the computer on all the points on the computer screen to show the way out of painting code, and then under the run-foot walk on his own by line, combined with the dot code, you can more easily link up these points. Or by guiding the preparation of encoded files for automatic connection.

Upon completion of this work, then these plans to get on the ground control, to take the field is not measured the amount of various data, and then interact with the computer editing to get the final topographic map.

Of course, using the above method, observation and the Secretary-foot staff requirements is relatively high. First in keeping with the tacit understanding, which is measured is over, what should be the next point should be measured Empathy; pairs of observers in the input numbers and letters require a higher level of proficiency, should normally be completed within 10 seconds (of course, some point number is no input). Division officers charged with second-foot indoor mapping work is in the process of surveying and mapping key personnel, which is why surface features (appearance) is a comprehensive trade-offs, etc. should be aware and should be determined before running a good race-foot-foot line, as far as possible avoid the costly mistakes.

After my practice has shown that use of the measurement of draft law to be more save trouble, fast. Station is only required on the coding and awarded two processes, while the Secretary-foot staff need to do is only reported through the walkie-talkie code, the process of placing the two prisms. The current measurement of a total station coordinates, it is basically less than 1 second, and some even reached a point of 0.3 seconds. By the Secretary-foot member of the impact of walking and other reasons, the measured surface features about 30 seconds to a point, the morphology of 1 minute or less can be said that the main time is from one point to another point of time, and in such a short period of time, sketches of personnel is basically not keep up with this idea and speed. After I measured in hours per day, each day is about 600 to 900 points can be measured. Moreover, the connection success rate above 95%.

Department of points for the broken identified, note the following points:

1. According to the rules of the proportion of construction (structure) building material detected only three points, the fourth point by the computer to complete.

2. Irregular topography should be able to multi-measuring some point, because in the traditional surveying and mapping, a number of small changes can be done manually, but computer simulation can not be more genuine reflect these actual terrain.

3. For the procedures specified in the order of drawing of the tiles, such as bridges, billboards, etc., preferably measured in accordance with their order.

In addition, attention should be paid the following matters:

1. The delineation of mapping units, as far as possible the natural boundaries for the sector, such as rivers, roads, etc., in order to facilitate measuring topographic map of the facilities, but also reduced the access side of the issue.

2. Point can be measured as measured as far as possible avoid using tape (ruler) the amount of take. Because the speed measured by total station is far from tape can take more than the amount, but accuracy will be higher.

3. The same type of surface features (appearance) should be measured first in order to avoid unnecessary within the industry, causing some trouble, of course, the actual situation on the ground can be used for flexible use. Also easily observed on station staff numbers and letters entered.

4. Contour measurement, in addition to measuring characteristics of lines, should be measured as much as some of the encrypted points, in order to meet the needs of computer modeling, but also reflected on in more detail the landscape.

5. As the Digital Mapping lot of work done on the computer, so how to strengthen the vetting of each unit on the solution. Especially in the surveyed area away from the location within the industry, there must be measures.

Since I is a preliminary exploration in this area, many aspects still need to perfect, hope you lot of pointing.