Qin Shuang, Li Jinhua

(Geological Museum of Henan Province, Zhengzhou 450016)

Abstract Vectorization of geological maps is an inevitable way to solve the bottleneck of geological map digitization problems, with the rapid development of computers and information technology, the digitization of the mapping method has been widely used, and machine-assisted compilation and drawing based on the digitization of geological maps is inevitable. In this paper, from the scanning vectorization of the actual starting point, from the basic preparation of MAPGIS to the specific operation and other aspects of the analysis, and combined with the practice of my work, and came to the use of MAPGIS vectorized image of a few points of experience.

Keywords: scanning; vectorization; raster image; vector graphics; MAPGIS; editing; digitization

The vectorization management of the original geological data has become a trend. The digitization of the map is no more than two methods, one is the use of digitizers for digitization, the source of error orientation error, acquisition error, etc., this method was popular in the 1980s and 1990s, but due to the large investment and high error, few people use it again; the other method is to scan the map into a raster image, and the use of raster-vector hybrid editing software such as MAPGIS, GTX, AutoCAD Overlay, etc. to transform into vector digital graphics.

1 Basic concepts of scanning vectorization

(1) Digitization. Digitization refers to the process of converting analog information such as graphics and text into digital information that can be recognized, processed, and stored by a computer.

(2) Vectorization. Vectorization is the process of converting raster data into vector data.

(3) Rasterization. Rasterization is the process of converting vector data into raster data.

(4) Raster Image. Also known as a raster image, it is an image that has been discretized both spatially and in terms of luminance. We can consider a raster image as a matrix, where any element of the matrix corresponds to a point in the image and the corresponding value corresponds to the gray level of that point, and the elements of the digital matrix are called pixels. A digital image is similar to a mosaic puzzle in that it is a rectangular pattern made up of a series of pixels, and is said to be a binary image, i.e., a bitmap, if all the pixels have two gray levels (black or white) and only two gray levels; otherwise it is said to be a grayscale image or a color image.

(5) Vector graphics. Before introducing vector graphics, we first elaborate the concept of vector objects. A vector object is an object described in the form of a vector, i.e., a comprehensive representation of the target in terms of direction and size. Examples are a straight line on a screen, a rectangle, a point, a circle, a filled closed area, etc. A vector graphics file is a descriptive file that is a combination of these vector objects. Vector graphics is computer software through a certain algorithm, the vector object description of the information in the display terminal to redraw the results.

Paper maps are initially saved as raster images (common formats are TIFF, BMP, PCX, JPEG, etc.) after being scanned by a scanner. Raster images have such drawbacks in the field of geographic applications: first of all, raster image files are saved for every pixel point of the image (regardless of foreground or background pixels), so their storage capacity is particularly large. In addition, we cannot edit any object (curve, text or symbol) in the image by modifying its attributes, copying, moving or deleting it, not to mention topology solving, but we can only edit all the pixels in a rectangular area at the same time. In addition, when the image is zoomed in or zoomed out, the image information will be distorted, especially when zoomed in the boundaries of the image target will be a step effect, just as the principle of the step effect occurs in the zoomed-in display of dot matrix Chinese characters.

The vector graphics is different. In vector graphics, each target is a single vector unit (point, line, plane) or a combination of vector units. Based on this data structure, we can easily edit each feature on the map, categorize the features, and solve the spatial relationship between the features. It also facilitates map browsing and output. Vectorization is the process of using digital image processing algorithms to identify various raster arrays on the source map as vector objects, and finally save them in a certain format. Vector graphics have a wide range of applications in industry, cartography, land use sector and other industries. Many successful software in these fields are based on vector graphics or cannot be separated from the participation of vector graphics, such as MAPGIS, AutoCAD, ARC/INFO, Corel Draw, GeoStar and so on.

With the continuous development of computer science, geography, cartography, remote sensing and photogrammetry, graphic imaging technology and database technology, GIS has become a powerful, perfect performance of the computer system, widely used in planning, land, surveying and mapping, construction, environmental protection, the military and many other departments, become an indispensable tool for government departments to carry out scientific management and rapid decision-making. It has become an indispensable tool for scientific management and rapid decision-making in government departments. MAP GIS, as a domestic GIS software developed earlier, has a certain number of users in China.

MAP GIS developed by China University of Geosciences is a GIS with international advanced level, which is divided into "graphic processing", "library management", "spatial analysis", "image analysis" and "map analysis". It is divided into "Graphics Processing", "Library Management", "Spatial Analysis", "Image Processing" and "Utility Services" 5 major parts, *** counting 21 subsystems. When using, the user according to their different needs, randomly select each subsystem.

2 MAPGIS scanning vectorization input

Scanning vectorization, through the scanner input scanning image, and then through the vector tracking, to determine the spatial location of the entity. For high-quality raw data, scanning is a time-saving and efficient way to input data.The main functions of MAPGIS Scanning Vectorization are:

Image Format Conversion Function - The system accepts the TIFF raster data format input from the scanner and converts it to the standard RBM of the MAPGIS system. format.

Vector tracking and guiding function - it can provide an all-around tour of the entire graphic, zoom in and out arbitrarily, and automatically adjust the position of the window when vectorizing to ensure that the vectorizing guiding cursor is always in the center of the screen. When tracking lines on a multi-gray level image, the centerline is guaranteed to be tracked.

Multiple Vectorization Processing Functions--The system provides interactive manual, semi-automatic, fully automatic refinement and fully automatic non-refinement vectorization methods, as well as full-image vectorization and in-window vectorization functions for users to choose.

Automatic recognition function--The system applies the technology of artificial intelligence and pattern recognition, and is the first one in our country to successfully realize grayscale scanning map vectorization and color scanning map vectorization, overcoming the fatal weakness of two-value scanning map vectorization, and making it possible for color maps to reach the one-time vectorization of all elements.

Editing and correcting function--The system provides functions of editing and modifying vectorized map elements (including point elements and line elements), which can be displayed at any size and scale at any time, and is convenient for proofreading; special elements such as Chinese characters and symbols can be called up directly from the system library, and can be automatically inputted and generated according to the given parameters.

3 M

3 MAPGIS basic concepts

MAP GIS map data according to the basic shape is divided into three categories: point data, line data and area data (i.e., surface data). Correspondingly, the basic types of files are also divided into three categories: point files (? .WT), line files (? .WL) and zone files (? .WP). Only including all the map data of the three types of files are superimposed, only to constitute a complete map.

3.1 Points

A point is a collective term for point-like objects in map data, a symbol or annotation whose position is determined by a control point. It is not a simple point, but includes a variety of annotations (English, Chinese characters, Arabic numerals, etc.) and specialized symbols (including circles, arcs, straight lines, pentagrams, kiosks and other types of symbols). It is different from the concept of "adding points on the line" in line editing, which is a coordinate point. All point map metadata is saved in point files (? .WT).

3.2 Line

Line is a collective term for the lines in a map, and MAP GIS edits all kinds of lines (e.g., dotted lines, provincial boundaries, national boundaries, contour lines, roads, and embankments) in line units as line elements. All line metadata are saved in line files (? .WL).

3.3 Zones

Zones are often also referred to as surfaces, which are closed shapes made up of arc segments connected at the beginning and the end, and an area formed by filling the closed shapes with color and pattern patterns. Examples include lakes, settlements, etc. All zone map metadata is stored in a zone file (? .WP).

3.4 Layers

In GIS applications, there are multiple types of geographic elements in the same file. For example, a line file may include contour lines, highways, railroads, rivers and other types of lines. In order to facilitate editing and management, in general, the same type of geographic elements can be placed on the same layer, for example: all the railroad lines are placed on the railroad layer, and all the contour lines are stored to the contour line layer, so that all the layers are stacked up to form a complete line file. In special cases, a layer can also be stored as a separate file.

3.5 Projects

A project consists of one or more point files, one or more line files, and one or more zone files.

3.6 Editing

After the data is inputted into the computer, it is necessary to enter the work of graphic editing, data correction, graphic contouring, neighboring graphic edging, error elimination, etc. The MAP GIS graphic editing sub-subsystem is used by the MAP GIS graphic editing sub-subsystem. By the MAP GIS graphics editing subsystem, topology editing subsystem, error checking and data correction subsystem to complete the above editing tasks.

3.7 Color Design

Color is an important element in the performance of geologic maps, which directly affects the expressive power and graphic effect of geologic maps. Therefore, the requirement of color for geological map is very strict.MAP GIS has made the color requirement for geological map, and designed a set of flexible, convenient and accurate color definition and color scale system based on the analysis of the printing characteristics of geological map.

3.8 Graphics Output

Graphics output is the last process in MAP GIS system, which is usually to display the required graphics data, after analysis, processing, editing, color, self-checking, error elimination, etc., and after basically complying with the requirements, the color sample maps are outputted with the color inkjet plotter, and the color sample maps are proofreading and system quality checking.

4 The use of MAPGIS vectorized image of a few points

In the process of using MAP GIS software, mapping units often encounter this or that tricky problem, for such problems, by consulting the MAP GIS reference manual and summarize the experience of the computer mapping work, came up with the following use of MAP GIS to draw a few points of experience of the geological map for reference of peers. For the reference of peers.

4.1 Scanning digitized maps, can be directly used for MAPGIS vectorization

We scan the map characterization of maps, black and white binary, grayscale and color (RGB mode) of three formats, MAP GIS supports these three formats of TIF raster files (?), which can be used for the production of geological maps. .TIF), you can open this raster file in PHOTOSHOP, save as TIF file can be.

4.2 Editing

As a geological map editor, not only should have the relevant professional and technical skills, but also have a certain field work experience, art specialties and conscientious attitude, in accordance with national standards, industry norms for editing and processing. Before graphic input, the editor must read the original map comprehensively, understand the content of the map, and check whether the plan view, map cut section, legend, text, geological events, mode map and so on are reasonable and coincide with each other. When editing the topographic map, it is necessary to add supplementary presentational information, such as triangulation points, highways, railroads, rivers, lakes, reservoirs, settlements and notes. Then, the contents of the map of the first error elimination, according to the requirements of the production of geographic maps, design layout, set up in accordance with the specifications of the font, font size, graphic finishing, color scheme, etc., which are closely related to the editor.

4.3 Proofreading

Proofreading is a repetitive systematic project, and is an important part of the publication, which generally needs to be proofread many times to eliminate errors and ensure its quality. Geological maps, although edited and processed under the MAP GIS system, often do not achieve the desired results. Then, color sample maps (or plain maps) must be output through color inkjet plotter for first and second proofreading and quality checking. Defects found in the inspection process, should be dealt with in a timely manner, so that the drawing standardization, standardization, to make up for the deficiencies of the compiler, to achieve the best results.

It is worth noting that: from the color inkjet plotter output color and color scale there is a certain difference (water-based color and the difference between oil-based ink), offset paper and coated paper paper fibers, brightness of the difference, as long as the geologic map according to the standard of color to determine the color number, the finished product of the printed color and color scale color is basically the same.

5 Conclusion

On the basis of scanning and digitizing, vectorization of the original geological data.MAP GIS, as a set of excellent GIS software, is used in many industries. We can collect data on topographic maps or other scanned raster maps through the "Input Edit" module of MAP GIS, vectorize them to form a complete file of points, lines and surfaces, and the results can either be printed out or analyzed in various applications, which is the development trend for us.

References

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[2] Qin Shuang, Li Jinhua. Computerized Cartography. Beijing: Surveying and Mapping Press. 1991.

[3] Proceedings of the Fourth National Symposium on Geological Archives. Beijing: Ocean Press. 2004.

[4] Yang Gongzhi, ed. File informationization construction practice. Beijing: China Archives Press. 2003.

[5] Dong Guochen, Hao Guojie, Chen Da, et al. Application of GIS in 1:50,000 Yuguan Town Formation Regional Geological Survey [J]. China Regional Geology, 1998, 17(4).