Why do we have coordinate projections?
The official definition is –
The irregular Earth surface can be substituted with the Earth ellipsoid, the earth ellipsoid is an irreducible surface , and the map is a plane that maps the points on the Earth's ellipsoid to the plane, called the map projection.
The understanding is that the earth is a ball, and what we want is a plan, and the process of this transformation is like the following: a luminous point shines toward the face to be projected, and the position after the projection of each point is recorded. The ultimate goal of the projection is to:
establishes a functional relationship between the coordinates (λ,φ) of the point on the Earth's ellipsoid and the corresponding coordinates (x, y) on the plane
In the process of expanding the ball into a plane, it is necessary to produce deformation error, which is mainly divided intoDeformation on
length, deformation on angle, deformation on areaFriends know that the error in the measurement is absolutely not tolerated. As a result, the generation of a variety of wave upon wave predecessors invented a variety of dazzling methods, and a projection to produce a projection coordinate system, which led to the ArcGIS in the light of a wide variety of materials eye coordinate system ... ：
Here are some ways to copy the projection transform from the teacher ppt. T_T Level Limited, seeking comfort
(1) Positive solution transformation
by establishing a close or approximate analytic relationship of projection transformation to another projection, the coordinate x and y of a projection are transformed directly from the digitized coordinates x to the other.
(2) Reverse Solution transformation
That is, the coordinates of a projection are reversed to the geographic coordinates (X,Y→B,L), thus the transformation from one projected coordinate to another projection coordinate (x,y→x,y).
(3) Numerical transformation
According to the two digitized points of the same name in the transformation region, interpolation method, finite difference method, finite element method, or undetermined coefficient method are used to realize the transformation from one projection coordinate to another.
Finally, summarize some common sense in the projected coordinate system:
- Basic scale topographic map of our country (1:1 million, 1:500,000, 1:250,000, 1:100,000, 1:50,000, 1:2.5, 1:10,000, 1:si) except 1:1 million, all using Gauss-G Gauss–krüger projection For geographical basis (.. Remember that is except for 1:1 million. Except for 1:1 million. Except for 1:1 million. ）
- The Lambert projection is adopted in the 1:100 topographic map of China, and its principle of distribution is consistent with the international one out of 10,000 maps projection, which is stipulated by international Geographic Society. (This is 1:1 million, Lambert Read catchy ah/' læmb?t/! ）
- Most of the provinces and regions of China and most of the maps of this scale also use Lambert projection and the same projection system of the Albers projection (positive axis and other area cut conic projection)
- Mercator Projection ( conformal cylindrical projection with positive axis ): Suppose the earth is enclosed in a hollow cylinder, its equator in contact with the cylinder, and then the Imaginary Earth Center has a lamp, projecting the shape on the spherical surface onto the cylinder, and then expanding the cylinder, which is a world map drawn by the standard parallels for the "Mercator projection" of zero (that is, the equator). Refer to http://blog.csdn.net/mygisforum/article/details/13295223
- This projection method ensures that the meridians and parallels are parallel and perpendicular to each other, are they familiar? However, the greater the deformation of this projection method to the polar area, so if you want to play the North and South Pole, you need another map.
- Web Mercator projection
- Google's projection of maps for his ladyship
- See http://www.cnblogs.com/GIS_zhou/articles/1525772.html, there's a chance to read it later.
- There is a wonderful answer, the first collection: Map commonly used projection method?
After-Class review of GIS: Spatial data processing-1.2 coordinate projection
