Qin Shuang Pu Hanyong

(Zhengzhou 4516, geological museum, Henan)

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

keyword scanning vectorization MAPGIS editing digitization

1 Introduction

The scanning vectorization processing algorithm is relatively mature. Generally, 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 maps contain a large number of geological symbols, and some mine maps (such as geological plan, profile, drilling or tunnel sketch) can not be vectorized by popular graphic vectorization software in the market. At present, some geological symbols can be vectorized by MAPGIS software by using the point, line and surface drawing function in the software.

2 Several methods of MAPGIS in drawing geological maps

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. Because of its professional characteristics, geological graphics are very different from other fields such as architecture. Geological bodies are mostly irregular, and the 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 collecting basic data, how to ensure the quality of data to the greatest 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 mapping, this paper summarizes the following methods that can draw geological maps quickly by using MAPGIS.

2.1 The scanner should keep the base map correct and standardized.

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 required to be uncompressed (LWZ is not selected). Therefore, it is best to open the raster file in PHOTOSHOP and save it as an image mode again.

2.2 topographic map drawing

when drawing topographic maps, topographic maps are mostly basic components, which generally account for the vast majority of the data of the whole map. The contour lines in topographic maps can be partitioned and edited by multiple people at the same time. Put the contour lines of different areas on the same layer and store them with different file names. Finally, we only need to merge and edit the contour lines with different file names on the same layer.

2.3 layering graphics

in the application of GIS, there are many types of geographical elements in the same file. For example, a line file 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 put on the same layer, for example, all railway lines are put on the railway layer, and all contours are stored in 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, a certain type of geological features, such as contour lines, isobath lines, features, strata, structures, lithology, drainage systems, chemical types, exploration projects, etc., are placed on different layers, and the point type, line type and area on this layer are consistent with the layer where they are located. The advantages of this method are as follows: ① By changing the points, lines and areas on a certain layer, it is impossible to change the point type, line type and area 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 don't 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 using the shape on a certain layer as a temporary file, all other layers can be closed and put forward separately, which is convenient for use.

2.4 use a special pattern library to fill a large area of 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. Choose this method to build the area, without searching the boundary, but need to build a closed boundary in advance; In addition, when constructing a closed boundary, try to use a broken line instead of a smooth curve.

(2) the filling method of points 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 mistaken. Most of the filled boundaries in geological graphics are irregular boundaries. When the map sheet is large and the content is complex, the local search area is greatly increased because the boundaries are not closed or crossed, and there are many repeated parts. At this time, it is very slow to determine the boundaries by point filling, and the efficiency of editing geological graphics is very low and impractical. Topology can make up for the above shortcomings, and the speed is fast. When searching the boundary by point, MAPGIS only searches the visible area, so it is more convenient and quick to solve the problem that the content of the drawing is simple and regular, which is close to square, quadrilateral and rectangle.

2.5 point editing

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

(1) The input point can insert a picture, 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 it with anchor points after input.

2.6 line editing

line is a general term for lines in the map. MAPGIS edits various line types (such as dotted lines, provincial boundaries, national boundaries, contour lines, roads and riverbanks) as line elements. All line graph metadata are 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 map by MAPGIS, you should always click Save. If a line is drawn too long and saved beyond the allowable range of MAPGIS, the contour file will be lost automatically, and the file cannot be saved, which seriously affects the editing speed. In addition, the contour line is too long, and the plotter can't identify it and print it, which is easy to lose files.

(3) In MapGIS 6.5 and 6.6, some lines will have burrs (such as Highway No.1), so you can choose to change the rounded corners into sharp corners or truncated corners in modifying the line types.

(4) array replication can be used to generate neat and standardized legend boxes conveniently and quickly.

(5) When inputting and modifying a line type, you should pay attention to whether the corresponding line type has an auxiliary line type or not. If the corresponding line type has no auxiliary line type, but the number is input, there will be inexplicable errors in editing and printing.

2.7 Area Editing

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

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

(2) Remember to delete the arc segment after deleting the unwanted area, 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 area primitives have transparent options, which mainly play a role in printing and color separation output. Generally do not use it, otherwise two or more overlapping areas will turn color when printed and published.

2.8 how to quickly convert MapGIS graphics into images

in the graphics output subsystem, open the engineering file, and you can find the commands to generate GIF, TIFF and JPEG 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 scanned raster maps, and vectorized to form a complete point, line and area file. This paper discusses the methods to improve the speed of drawing geological maps by MAPGIS from aspects of work preparation, work strategy and skills, and parameter setting.

references

computer mapping. Beijing: Surveying and Mapping Publishing House, 1991

Proceedings of the 4th National Symposium on Geological Archives. Beijing: Ocean Publishing House, 24

Geographic Information System Reference Manual. Beijing: School of Information Engineering, China Geo University (Wuhan).