The Characteristics and Drawing Method of Map Printing Technology (Part 2)

Next, I will introduce the GISGIS software developed by Wuhan China Information Engineering Corporation of China University of Geosciences to introduce the process of GIS mapping.

The basic process flow for drawing a map can be simply described as: Scan → Vectorization → Dot Line Edit → Generate Standard Box → Error Correction → Frame Mosaic → Build Area → Edit → Generate Project File → Map Output.

The scanning input method provided by the GIS's intelligent scanning vectorization subsystem scans the original image directly by a scanner, stores it in a grid or image file (such as TIFF format), and then converts it into vector data through vectorization. Go to the line file (*.wl) or point file (*.wt) and edit and output. In addition to the vectorization of the binary scan map, the grayscale scan map and the color scan map can be automatically identified and tracked. In vectorization, functions such as point back, point guidance, and selection can effectively select the desired graphic information, eliminate unnecessary elements and noise points, reduce the workload of later graphic editing and finishing, and can simultaneously layer graphics. deal with.

The graphic editor provides functions for editing the spatial data and graphic attributes of the three types of primitives: point, line, and surface. Topological processing has changed the method of artificially establishing topological relationships, making it relatively easy to perform relatively complex tasks such as area input and sub-zone input, which greatly improves the efficiency of map entry and editing. Use the load file function to load the original digitized point and line files into the work area and modify the errors. When creating a zone, first save the edited line file, then delete lines that are not related to the zone (such as rivers, roads, and fault lines), or separate the lines from the lines that make up the zone using the layer manipulation function. Then handle the intersection of the curves, including line clipping and intersection matching. The first step is to create a zone by "revolving the line" and then using "topological reconstruction". Then, the subarea search is performed to establish the nesting relationship of the zone, and finally the zone file is saved.

In the process of scanning or digitizing the graphics, due to the error of operation, the precision of the digitized equipment and the deformation of the drawings, the graphics after the input may be partially or entirely deformed. The errors of graphic data and attribute data mainly include: incomplete data, including spatial points, lines, surfaces, data loss, omission of regional center points, line break caused by raster data vectorization, etc.; spatial data position is not Accuracy, including the inaccuracy of space points, line segments are too long or too short, line segment breaks, non-coincidence of adjacent polygon nodes, etc. The scale of spatial data is inaccurate, deformed, incomplete, and connected incorrectly. In order to eliminate the distortion of the input graphics and achieve the accuracy of the graphics, after the graphics are input, an error correction system can be used to correct the occurrence of one or more of the entire graphics or graphics in the graphics or graphics caused by mechanical precision, manual error, and drawing distortion. The position deviation. The system automatically collects the values ​​of the actual control point and the theoretical control point, establishes a correspondence between the actual value and the theoretical value, and calculates the error coefficient of each actual control point, so that it can be corrected according to the obtained error coefficient. The point-line surface data around each actual control point eventually achieves the purpose of correcting the entire point-line surface file. Corrected maps are more accurate.

When all the work is completed, based on the project file described in the layout, we compile the point, line, and surface files into a project file. The process of combining the multiple files of the entire map, that is, drawing a map, can be output.

GIS has prepared a variety of output functions for Postscript format files, including PS files for the Peking University RIP RIP, PS files for other RIPs, and EPS files conforming to the Adobe AI standard format. The Postscript output file is directly transmitted to the laser imagesetter, and four color films can be output.

The use of geographic information systems for mapmaking has unparalleled advantages, which are embodied in:

1. Graphic input operation is relatively simple, reliable, and can meet the needs of the project

GIS has multiple inputs such as digitizer input and scan-only input, which can automatically perform line segment tracking, node adjustment, line segment cutoff and extension, automatic generation of polygon topology, nonlinear correction of drawing deformation, and errors. The automatic detection greatly simplifies the graphical input operation, ensures the reliability of the input, and is particularly suitable for relatively large graphic input.

2. Making published maps with high accuracy

GIS has rich graphics editing tools and powerful graphics processing capabilities. Its functional design is in line with the cartographic process of China's maps. It can correctly handle the escaping of the map elements and the gradual change of river lines. It can easily make layout annotations of maps, automatically generate standard map frames, and can perform various geographic coordinate conversions. Conveniently design definition lines, icons, fill patterns, and chromatograms. Users can output graphics to various graphics devices "what you see is what you get." It also has an interface with the standard page description language Postscript, capable of outputting color-stained plate-making films and producing high-precision graphics.

3. Integrated management of graphic data and application data

In the GIS, the map's graphic data is stored in strict dot-line topological structure, and is managed by a graphic database. At the same time, various professional application data are managed by a professional attribute database, and the two are connected by keywords to realize graphic data. Integrated management with application data. The image registration mosaic system provides a powerful control point editing environment to complete the editing and processing of the geometric control points of the image, thereby realizing the registration between images, the registration of images and graphics, the mosaic of images, and the image geometric correction in real time. Geometric transformations, gradation transformations, etc.

4. Up to thousands of maps can be seamlessly stitched

GIS can automatically concatenate large-scale rectangular maps, small-scale sector maps, and automatic or semi-automatic elimination of edge-to-edge errors between maps, as well as cross-map terrain retrieval and attribute data retrieval. In addition, graphics are cropped across the map to meet the needs of different applications.

5. The variety of maps has been added, the scope of services has been broadened, and three-dimensional, visual stereograms, surface cut density maps, slope maps, slope maps, etc., which are difficult to achieve with conventional methods, have been made.

6, digital maps can be easily applied to the computer to read, analyze, manage and input terrain information in various fields (such as GIS information acquisition and output).

Digital maps are easily stored, and the storage is not deformed, which improves the accuracy of maps and facilitates remote transmission and processing.

7. Accelerated the drawing speed, shortened the drawing cycle, improved the process of drawing and plate printing

The development of science and technology is like dominoes. The accumulated energy is increasing and the speed of development is getting faster and faster. With the continuous advancement of science and technology and the constant emergence of new technologies, mapmaking and printing of maps will develop in a more simple, practical and convenient manner.

Source: Department of Mathematics, China University of Geosciences (Guo Qiong Julie)