Full Process of map screen digitalization

Map screen digitalization

Map digitalization is currentlyGISThe main source for obtaining map data, while map screen digitalization is a common method of this source. Compared with manual tracking digitization, it has the advantages of low cost and fast speed, with the popularity of computers and the enhancement of digital software functions, it has become the first choice for most people to obtain map vector data. So what is map screen digitalization? What specific steps does it have? What problems should we pay attention to during the digitization process? This article is based on my understanding of screen digitalization and my experience in related work, and does not pass Expert identification, so it is inevitable that there is something wrong.

What is screen digitalization first?

Screen digitalization is based on digitization(Vectoring)Software (suchR2v,ArcMapMediumArcscanModule.

What are the digitization methods and steps?

Before answering this question, you must first know that a map is a plane image after the Earth surface phenomenon is projected, after a map is scanned, it is only an image (in this sense, the electronic images we usually see are no different),The coordinates displayed after being loaded into the software are only the coordinates of the software display window. On the other hand, the digital layer must have the actual plane coordinates of the map, therefore, we need to first convert the map display window coordinate system to the actual map coordinate system before map digitization. This will use the map registration operation, which will be described below.

All and digital operations in this article are based onArcMapInArcscanModule (ArcscanIs a very powerful vectorized module), the map data used is1:510 thousand topographic maps. The part number is13-52-112-Ding, which usesBeijing54Coordinate System, projection is6Gaussian-gram projection of the Degree band, from which we can know that the central meridian of the projection is129°E,1(Because of confidentiality, the drawing is only partial ).

Figure1MAP range used for demonstration

The specific digitization steps are as follows:

1OpenArcMap, LoadArcscanModule (right-click in the blank area of the menu bar and selectArcscan), And then on the menu barTools/extensions, SetArcscanSelect the check box before and load the map registration module.Georeferencing,Same method loadArcscanSame. Figure2As shown in:

Figure2 Load Module

2, IsData FrameSet the map coordinate system. We can see from the previous introduction that the coordinate system is consistent with the real Coordinate System of the map, that is,Beijing54Gaussian in geographic coordinate system-Kerenge projection. The specific settings are described earlier.3As shown in:

Figure3Set map coordinate system

3Load Map

4, UtilizationGeoreferencingMap registration (we recommend that you firstGeoreferencingUnderAuto adjust. Click Icon to select a control point. The control point selection principle is to know the coordinates of the points (here is, if it is a picture to the image registration, you need to select the actual position unchanged points ), the four corners of the map have longitude and latitude coordinates, so select these four points first (the specific method is to enlarge the map and click at the intersection of latitude and longitude, then click it at any other location (maybe it is wrong, don't be busy, and I will explain it below). This completes the initial selection of a control point, then, select the remaining points in sequence.

Click the icon after the selection. , You can see4All tables.

Figure4 Coordinates of the Control PointLink Table

You can seeXmap, ymapField, put this on one side first, and then perform the coordinate (expressed by longitude and latitude) to convert the plane coordinates (The unit of the plane, which is meter), even if48°50′N,127°45′EAfter Point Projection, how much is the plane coordinate on the map. The conversion requires corresponding projection parameters. For convenience, you can use some small software for coordinate conversion. After the coordinates of these points are converted, the corresponding InputXmapAndYmap.5As shown in:

Figure5After the coordinates are modifiedLink Table

After confirmationGeoreferencingOne time in the drop-down list , , The format of map output and output is optional. We recommend that you useTIFFormat.

5, Map digitalization

Create a layer that needs to be digitalized, such as a contour layer. The Coordinate System of the layer should be consistent with the actual map coordinate system. Load the layers and map files that need to be digitalized (the files after the map registration has been completed) and the grid data of a certain band of the map file (suchBand2), Binarization the single-band Raster image,Start editingThen you can seeArcscanThe toolbar is activated.

Note:ArcscanThe vectoring tool can only be used in the case of binarization raster data, while loadingRGBThe Synthetic Map data is used to facilitate Manual Interference Vector tracking. Of course, the data can not be loaded (as a result, the workload is greatly increased and error-prone ). You can use this function to hide a single-band image.ArcscanThe element of the vectorized map is the "original map" synthesized by "true color", which is easy to operate.6As shown in:

Figure6Examples of vectorized contour lines

Some suggestions:

1Each time a factor is digitalized, the attribute value is added to it;

2If the automatic tracking is ineffective, You can reset the binary classification range;