1. Overview
Some time ago, we published an article about how to use the Water Jingzhu Universal Map Downloader to download geological maps. "Geological maps, special maps and other professional maps downloads" click to understand the original text. Today, taking ArcGIS as an example, combined with years of work experience, we will introduce the skills of vectorization of geological maps.
Water injection universal map downloader download geological map
2. base map registration
different scale maps have different registration accuracy requirements:
1: 200,000 geological maps, registration error cannot be higher than 20 meters;
1: 500,000 geological maps, registration error cannot be higher than 50 meters.
scans original drawings with good quality, and only one registration of more than 4 control points can be achieved by registering them in one go; original drawings with poor scanning quality must be registered with second or even three times. In ArcGIS, at least 6 control points can be registered with second registration, and at least 10 control points can be registered with three times. The control points should be evenly distributed on the picture. In order to facilitate registration, it is necessary to use image processing software to process some severely aging pictures to remove aging colors and restore their original colors before registration.
3. Establishment of Feature Class in Geodatabase
Establishment of feature classes is the main content of geodatabase establishment work. In the vectorization work of geological maps, the main feature classes involved include polygon features, line features, and point features. The surface elements related to geology include: invasive rocks, sedimentary rocks, metamorphic rocks, alteration zones, various vein rocks, etc.; the main linear elements are: faults, geological boundaries, etc.; the main point elements are mainly various mineral points. In addition, there are non-geological elements such as water systems, roads, towns, and settlements.
In the process of establishing a feature class, you must set the name (Name), alias (Alias), type (Type), geometric features (Geometry Properties), coordinate system (Coordinate System), XY tolerance (XY Tolerance), attribute table fields (Fields), etc. Names are the basis for computers to identify feature classes. The settings should be concise and clear, and they should be clear and clear. If necessary, they can also set up an alias. Please note that the alias are only for user identification and are not the basis for computer identification. The settings of the types (i.e., surfaces, lines, points), geometric features (i.e., 3D data that includes Z values), and coordinate system must be the same as the base map, so as to ensure that the vectorized data is consistent with the original data. The XY tolerance should not be set too large, otherwise it will affect the accuracy of the data. We can set it according to the specific accuracy requirements of the base map, such as a geological map of 1:200,000. Set this value to 1 meter to meet the accuracy requirements. The setting of the attribute table field is very important, so it is introduced in the next section.
4. attribute table of feature class
attribute table creation and filling of feature class attribute table are the main and key contents of vectorization work. The creation process of the attribute table mainly includes the naming of the field and the selection of field types and lengths. For example, for invading rocks, the local name of the rock body, rock type, lithological symbol, lithological code, rock color, rock structure, rock structure, rock structure, lithological phase, main minerals and content, secondary minerals and content, contact relationship with surrounding rock, contact surface direction, contact surface tendency, contact surface inclination, surrounding rock era, formation era, mineral-containing properties, etc. For sedimentary rocks and strata, the local name of the strata, the symbol of the strata, the era of the strata unit, the color of the main body of the rock combination, the main sedimentary structure of the strata, biological fossils, and the shape of the strata, etc. can be set.
field type, the most commonly used in geological map vectorization are: Short Integer, Long Integer, Float, Double, Text, because it is selected according to the characteristics of the field data. The length of the
field is too short and will not be enough to use. Too long will cause data redundancy, especially for Text types.
geological map
5. vectorized tracking of points, lines, and surfaces
vectorized tracking of points, lines, and surfaces must follow a basic principle, that is, be faithful to the original picture and consistent with the original picture.Vectorization of
points is very easy. Just place the points on the map to the appropriate size and position them at the center. Vectorization of
lines is also relatively simple. It is required to place the lines at the appropriate thickness and track them with the mouse in turn. Since the scanned base map will be square grids when enlarged to a certain extent, some people advocate enlarging the base map to a large multiple, and pointing the mouse in the center of the grid when tracking, so that the graph can be accurately measured to the grid. In fact, this statement is wrong. There are two disadvantages of doing this: one is slow speed and low efficiency; the other is that the consequences of doing this may not be faithful to the original picture, but will instead cause some subtle mistakes. As shown in Figure 1, the lines of the base map were originally smooth, but according to grid tracking, many tiny zigzags appeared. It is important to realize that any raster image will appear square rasters when enlarged to a certain extent. This is a major limitation of raster data. These lattices are not the true reflection of the original base map, but the approximate expression of the original lines. What we need to track is not the center point of each square, but the overall trend of all squares.
Correct and error tracking methods
A: Correct method, grasp the overall trend of all grids, smooth lines
B: Wrong method, tracking according to the center of each grid, many tiny serrated
can be seen, so the so-called "detailed" is relative, and sometimes too detailed will cause errors. Therefore, the correct tracking method should be: grasp the overall trend of all squares and let the lines run through this trend to the greatest extent. Generally speaking, the lines should be smooth. Vectorization of
faces is the most complex and tedious, and the workload is very huge. Generally speaking, there are four types of topological relationships between faces: separation, adjacent, intersected, and inclusion. To handle the vectorization problem of the surface well, we must correctly handle these four topological relationships. The traditional method is: if two faces have common edges, you should use tools such as capture and tracking when making a graph to ensure that these two faces strictly overlap on the public edge. If one face contains another face, you need to use a cutting tool when making the drawing, and then you can create a new face inside the large face.
It is obvious that the above vectorization method about faces is a completely conventional method in ArcGIS. This method has to be tracked repeatedly every time it encounters a common edge, which is time-consuming and labor-intensive, and it is very cumbersome to operate. If you are not careful, you will make mistakes. The most common mistake is to produce some small triangles at the junction of multiple faces. Such errors are also very troublesome to modify.
is precisely because of the above shortcomings of the traditional method that we strongly do not recommend this, but a faster method is used: vectorize the boundaries of all polygons as line elements according to the vectorization method of line elements, thus forming a line element class called the original line of the graph. Note: When vectorization, the boundaries of all faces must be closed, and all lines can only be tracked once. Then use the "Feature to Polygon" tool in the toolbox to convert the original lines to the surface. The advantage of this is that it is simple to operate, saves time and effort and greatly reduces the chance of error.
Use the "Feature to Polygon" tool in the toolbox to convert any closed curve into surfaces
6. Legend
This part of the operation belongs to the category of visual expression. ArcGIS has powerful legend generation tools. As long as you are familiar with the operation methods, you can generate any required legends.
should save it as a Style file after generating the legend. Once the Style file is generated, it can be modified and managed using Style Manger.
If you see the legend you have made in the past in the future, you only need to call the style you have made in the past. You can also save Style in sets. In the future, if you encounter such a legend, you only need to use the "Match to symbols in a style" method, which can save a lot of time.
Match to symbols in a style
7. Multi-person division of labor and cooperation skills
If you want to complete a large-scale picture piece in a short time, you must conduct multi-person division of labor and cooperation.Multiple division of labor and cooperation requires each member to strictly implement unified standards. Only in this way can the various parts of each person be perfectly integrated and connected.
Before the work begins, a division of labor can be established diagram box , each person is responsible for part of it, and when everyone's work is completed, the combined picture must be carried out. Since everyone works according to a unified division of labor chart frame, everyone's charts can be well connected when combined. Some lines and surfaces divided into two by the frame need to be restored to their original state with the Merge tool.
Merge tool can eliminate division of labor drawing frame lines
When the division of labor cooperation is carried out, you can set the division of labor drawing frames, and each person completes one of them. When combining the drawings, use the Merge tool to eliminate division of labor drawing frame lines.
division of labor and cooperation requires a high degree of consistency. The standards that everyone implements should be refined into all aspects, such as the distance between each node during vectorization tracking, whether each character is uppercase or lowercase when filling in the attribute table, whether it is full or half-width, etc. If every detail is unified, the chance of error will be reduced to a very small, and the entire data will be integrated after the combined picture.
8. metadata
Some people call metadata "data of data", which is equivalent to the data instruction manual. For a complete set of data, metadata is essential. However, the author investigated some vectorized staff and found that the importance of metadata has not been paid enough attention to, which is very inappropriate. For example, when shopping in a shopping mall, we will think that the quality of products without instructions is unreliable. Similarly, data without metadata will not be too reliable.
ArcGIS provides us with rich and powerful metadata editing tools. Enter ArcCatalog, select the data you want to edit, and then click the data editing tool to edit metadata. Click each tab to edit each project.
metadata editor
9. summary
vectorization of geological maps is a basic task that requires meticulousness, and high-quality vector data will provide reliable data support for future research. The working group where I work, before mastering the above methods, each person can barely complete a 1:200,000 regional geological map in 6-7 days. After mastering the scientific and efficient methods, each person can complete the same workload in 2-3 days. This shows how important it is to master scientific and efficient vectorization methods.
