Geographic direction of GIS graphics - a problem that is often overlooked
Xu Qingrong, this article (Wuhan University)
On conventional maps, the geographic direction of keeping graphic symbols (or notes) is an important drawing rule, which is valuable experience accumulated in the production of maps since ancient times. This rule helps to enhance the readability and expression of the map. It should also be applied to a map output by the GIS (geographic information system) or electronic map software because the screen map is also available for people. But unfortunately, there have been almost all of which have almost all the software, which has been developed for many years of development history.
The graphic output of the GIS is generally geographical graphics, such as a map or statistical chart of different than the exemptions of various purposes. The map is the Earth surface (approximate ellipsoid surface) projection to the plane according to a certain mathematical method, and expressed with a specified symbol and text. Obviously, the direction of latitude and longitudinal direction of projections is generally impossible to consistent with the plane right angle axis direction. This is more obvious on a small scalar map (such as the world map, national map and the provincial map, etc.), and there is often a certain interval (degree) on this picture, which is a set of curves or straight lines, generally Not parallel to the direction of the right angle coordinate axis. Some maps are divided by latitude and latitude (such as various topographic maps), and its silhouette is bounded (weft) line (approximately confident), and deviates from the right angle coordinate axis direction.
An important feature of the GIS graphics is different from other graphics is the geographic directionality of graphics. The graphics symbol and the notation direction are uniformly consistent with the geographic element extension (which is easy to understand), and is also required to be consistent with the latent line direction. The reason why the symbol (or the annotation) direction is consistent with the direction of the latitude and latitude is: one is to facilitate the real geography direction (something or north of the north) on the identification map, and the second is that the symbol (or the annotation) direction is coordinated with the latitude network cable. Reading a "surface sensation", which triggers Lenovo distributed to natural landscape spherical. Of course, if the symbol (or the annotation) direction is consistent with the latitude and latitude, the symbol (or text) will be inverted or too skew, and this principle should be discarded, and the symbol (or the annotation) direction should be discarded.
The following is talked about several specific issues that are consistent with the direction of the latitude and latitude direction.
1. What is the direction of symbols (or annotations) and their consistent with the direction of latitude and latitude
The so-called symbol (or the annotation) direction has two layers:
(1) Arrangement of group symbols (or text). According to the shape characteristics of the geographic element, there is a horizontal direction, vertical direction, and the direction of the geographic feature distribution (in any line or any curve).
(2) The direction of a single symbol (or text). There are upright (hierarchical direction), with geographic elements to parallel, and three kinds of geographical elements.
The so-called symbol (or note) direction is consistent with the direction of the latitude and latitude, and it is:
(1) Where the horizontal arrangement is directed, it must be parallel to the weft (not the X-axis).
(2) Where vertical arrangements, it is necessary to parallel the line (not Y-axis) of its location.
(3) All single symbols (or text) of the Direct direction (or text), the weft (not X-axis) of the position (not the X-axis) is perpendicular to the top of the symbol (or text) toward the north (parallel to the warp rather than the Y-axis). 2. How to achieve the same direction with the tendency
The wiring direction on the map is referred to as the angular coordinate Y-axis of the right angle coordinate Y-axis, and the δ of the moon is not the same, and the δ can be calculated from the position (x, y) according to the corresponding map projection formula. It is negative. As long as the symbols (or notes) are corrected in the direction of the δ, the direction of the symbol (or the annotation) is consistent with the latitude and latitude direction. Obviously, the GIS software should have an automatic direction correction function, rather than stupidity, etc., when the graphic editing is changed, it is manually operation to rotate.
3. Example
The following figure is a fictional schematic (the light blue lines in the figure are wireless and weft). For more example, see all types of maps or wall charts formally published.
Graphics Software Development Tools UGS has the above-described direction correction function. When the application is called the UGS drawing (or the annotation) function, the symbol (notation) direction can be automatically adjusted when the direction correction value Δ (obtained by a certain algorithm) is given, so that the direction of the latitude Consisten to, UGS is posted on 9CBS (graphics processing class), download:
http://www.9cbs.net/cnshare/shtm/18.shtm
Author published in 9CBS related articles:
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Contact: Short information can be sent to XQR at the 9CBS forum.
