Discussion on the content of MAPGIS and some methods of drawing geological map

(geological museum, Zhengzhou, Henan 4500 16)

On the basis of scanning digitalization, the original geological data are vectorized, and by consulting MAPGIS manual, the experience of computer drawing is summarized, and several methods of drawing geological maps quickly by using MAPGIS are summarized.

Scanning vectorization MAPGIS editing digitalization

1 Introduction

The scanning vectorization processing algorithm is relatively mature. Usually, the conversion of scanned raster images into vector maps goes through the processes of image binarization, smoothing and thinning, coding and vector line extraction. Geological map contains a large number of geological symbols, and some mine maps (such as geological plan, section map, drilling or tunnel sketch) can not be vectorized by popular graphic vectorization software on the market. At present, some geological symbols can be vectorized by using the function of drawing points, lines and surfaces in MAPGIS software.

Several methods of drawing geological map with MapGIS

With the continuous development of computer science, geography, cartography, remote sensing and photogrammetry, graphic image technology and database technology, geographic information system has become a powerful and perfect computer system, and MAPGIS has been widely used in geological fields such as geological investigation and evaluation, environmental evaluation, mine management, groundwater monitoring and topographic survey. Geological mapping is very different from other fields such as architecture because of its professional characteristics. Geological bodies are mostly irregular bodies, and their boundaries are mostly composed of smooth curves. Large areas of color blocks, patterns and patterns are often needed to represent geological bodies with different properties, such as different rock masses, geomorphic units, geological structures, hydrochemical properties, easy zoning, prevention and control planning areas, etc.

Data is the basis of all information processing and the most important resource. In the process of basic data collection, how to ensure the data quality to the maximum extent and reduce the repetitive workload is one of the most critical issues in basic information work. In view of these factors, by consulting the MAPGIS manual and summarizing the experience of computer drawing, the following methods of drawing geological maps quickly by using MAPGIS are summarized.

2. 1 Scanner inputs graphics to keep the base map correct and standard.

MAPGIS does not support all raster file formats. It only supports TIF raster files in black-and-white binary, gray and color (RGB) formats, and it is also uncompressed (LWZ is not selected). Therefore, it is best to open the raster file in PHOTOSHOP and save it in image mode again.

2.2 topographic map drawing

When drawing topographic maps, topographic maps are mostly basic components, generally accounting for the vast majority of the whole map data. Contours in topographic maps can be divided and edited by many people at the same time. Put the contours of different areas on the same layer and store them with different file names. Finally, we only need to merge and edit contour lines with different file names on the same layer.

2.3 Layered graphics

In the application of GIS, there are many types of geographical elements in the same file. For example, line files may include contour lines, highways, railways, rivers and other types of lines. In order to facilitate editing and management, in general, geographical elements of the same type can be placed on the same layer, for example, all railway lines are placed on the railway layer, and all contours are stored on the contour layer, so that all layers are superimposed to form a complete line file. Under special circumstances, a layer can also be saved as a separate file, as shown in figure 1.

Figure 1 Modify the layer name

On each layer, some type of geological features, such as contour lines, isobath lines, features, strata, structures, lithology, water system, chemical types, exploration projects, etc. , placed on different layers, the point type, line type and area on this layer are consistent with the layer. The advantages of this method are as follows: ① By changing the points, lines and surfaces on a certain layer, it is impossible to change the point types, line types and surfaces of all geological bodies on the result map, which speeds up the editing and modification and reduces omissions; (2) By closing the layer where the shapes that do not need to be edited temporarily are located, these shapes will not be regenerated when the graphics are regenerated, which improves the speed of graphics regeneration; (3) When a shape on a certain layer is used as a temporary file, all other layers can be closed and put forward separately, which is convenient to use.

2.4 Use a special pattern library to complete the filling of large-area color blocks and lithologic patterns.

The speed of pattern filling mainly depends on the speed of determining the boundary. MAPGIS provides two methods to determine the filling boundary:

(1) topology mode. Choose this method to build the area, without searching the boundary, but you need to build the closed boundary in advance; In addition, when constructing a closed boundary, we should try to use broken lines instead of smooth curves.

(2) The filling method of the midpoint in the graphic area. This method does not need to construct the boundary in advance, but it needs to search the boundary in the direction indicated by the arrow in the visible area, and the direction must not be wrong. Most of the filling boundaries in geological graphics are irregular boundaries. When the map is large and the content is complex, because the boundary is not closed or crossed, the local search area is greatly increased and there are many overlapping parts. At this time, it is very slow to determine the boundary by point filling, and the efficiency of editing geological graphics is very low and impractical. Topology can make up for the above shortcomings and is fast. When searching the boundary point by point, MAPGIS only searches the visible area, which solves the problem that the graphic content is simple and regular and close to square, quadrilateral and rectangle, which is more convenient and fast.

2.5 point editing

Point is the general name of points in map data, and it is a symbol or note whose position is determined by control points. It is not a simple point, but includes various labels (English, Chinese characters, Arabic numerals, etc. ) and special symbols (including circles, arcs, straight lines, five-pointed stars, pavilions and other symbols). Different from the concept of "adding points online" in line editing, the points of "adding points online" are coordinate points. All point map metadata are saved in point files (*. wt)。

(1) The input point can insert pictures, but the path cannot be changed after insertion;

(2) Array replication points can generate a series of standardized and tidy points;

(3) The anchor point is very important for the disaster point input of the zoning project. This method is to input the coordinate values of GPS, first move the lower left corner of the map as the data corresponding to the coordinate values, and then modify them with anchor points after input.

2.6 line editing

Line is a general term for linear objects in a map. MAPGIS edits various line types (such as dashed line, provincial boundary, national boundary, contour line, road and river bank) as line elements. All line chart metadata is saved in an online file (*. wl)。

(1) The choice of polyline, streamline and smooth line should be correct.

(2) When editing contour file lines in topographic maps with MAPGIS, always click Save. If a line is drawn too long and saved beyond the allowable range of MAPGIS, the contour file will be automatically lost and the file cannot be saved, which seriously affects the editing speed. In addition, the contour line is too long, so the plotter can't recognize the printing, and it is easy to lose files.

(3) In 3)MAPGIS6.5 and 6.6, some lines will appear burr phenomenon (such as 10 highway), so you can choose to change the rounded corners into sharp corners or truncated corners in modifying the line type.

(4) Using array replication, a neat and standardized legend box can be generated conveniently and quickly.

(5) When inputting and modifying line types, pay attention to whether the corresponding line types have auxiliary line types. If the corresponding line type has no auxiliary line type, but a number is entered, there will be inexplicable errors in editing and printing.

2.7 regional editor

Area, also known as surface, is an area formed by closed graphics composed of arc segments connected end to end, filled with colors and patterns, such as lakes and residential areas. All area map metadata is saved in the area file (*. wp)。

Pay attention to the accuracy of (1) area color number. If you use color numbers that are not available in the system library when editing, you may find errors when printing.

(2) After deleting the unnecessary area, remember to delete the arc segment, otherwise the file printing positioning may be wrong, and the file memory will also make people feel inexplicably larger.

(3) When editing primitive parameters, point, line and surface primitives have transparent options, which mainly play the role of printing and color separation output. Generally do not use it, or two or more overlapping areas will change color when printed and published.

2.8 MAPGIS graphics quickly converted into images.

In the graphics output subsystem, the commands to open engineering files and generate GIF, TIFF and JPEG can be found under the "raster output" menu. When the map sheet is large, EPS format needs to be generated; If JPEG format is generated, it is easy to open files when browsing pictures.

3 Conclusion

On the basis of scanning digitization, the original geological data are vectorized. Through the "input editing" module of MAPGIS, data are collected from topographic maps or other scanning raster maps and vectorized to form a complete point, line and area file. This paper probes into the methods for improving the speed of drawing geological maps by MAPGIS from aspects of work preparation, work strategies and skills, and parameter setting.

refer to

Computer drawing. Beijing: Surveying and Mapping Press, 199 1.

Proceedings of the 4th National Symposium on Geological Archives. Beijing: Ocean Press, 2004.

Geographic information system reference manual. Beijing: School of Information Engineering, China Geo University (Wuhan)