GIS coordinate system defined in the division operation and in particular inside gis

GIS coordinate system definition and division

GIS coordinate system can be said to be the soul of GIS, GIS display are inseparable from any of a coordinate system. Typically GIS coordinate system may be divided into spatial rectangular coordinate system, the world coordinate system and the spatial plane rectangular coordinate system. According to the division manner of ESRI's GIS coordinate system and can be divided into geographic coordinate system, projected coordinate system, in fact, the two division manner but just not the same name, the essential meaning is the same, here we named ESRI GIS to coordinate pair Department to explain.

(1) geographic coordinates (geographic coordinate system)

ESRI is a geographic coordinate system of the geocentric coordinate system to the Earth's center of mass as the origin of the coordinate system, the direction east-west direction of longitude, latitude direction north-south direction, and the angle between the prime meridian point on Earth in longitude direction is the longitude of the point, the point on the latitudinal direction of the angle between the equator latitude, longitude and latitude coordinates in fact, expressed in latitude and longitude coordinates of any point on Earth.

In order to define the concept of the coordinate system requires extraction ellipsoid, measuring and mapping to use in place of the earth spheroid sphere, commonly referred to as the spheroid earth ellipsoid, spheroid referred. It is a mathematical surface a rule, so people view them as a mathematical surface of the earth body. Defined ellipsoid has three important parameters, the radius of the major axis (equatorial radius) a, a minor axis radius (radius polar) B, and a flat ellipsoid of [alpha], where α = (ab) / a. Thus the definition of a spheroid requires two parameters, the third parameter can be determined by two parameters known.

Another important concept is the reference plane, a plane with a specific ellipsoid to approximate the ellipsoid specific area, for a known ellipsoid, translated by (x, y, z), rotation (x, y, z) and obtained a new scaling ellipsoid, the ellipsoid is the datum. It is to say, by a known datum ellipsoid (two parameters) with 7 and parameter definitions. Therefore, ellipsoid and datum to-many relationship. Example: WGS84, Beijing 54 defines an ellipsoid, Beijing 54 used is Krassovsky ellipsoid, and Beijing plane coordinate system 54 is Krassovsky local ellipsoid plus 7 transformation parameters are calculated, and converted 7 of the coordinate system parameters used in China and Russia using seven parameters parameter is obviously different. For China, the local coordinate system conversion parameter 7 is a state secret, the needs of the local Bureau of Surveying and Mapping, of course, also be considered by the national anti-known anchor points and using latitude and longitude coordinates of the GPS acquisition, it is said to be illegal.

To summarize, the geographic coordinate system is defined by a plane, two parameters need ellipsoid major axis a, and a flat rate f is defined, the reference plane is defined by an ellipsoid and 7 ellipsoid transformation parameters.

(2) projected coordinate system (Projected Coordinate Systems)

A map projection is the use of certain mathematical methods put through the Earth's surface, and the theoretical weft conversion method on the plane. Since the earth is a slightly wider equatorial poles slightly pear-shaped flat irregular sphere, so the surface is not a flat surface, so the use of any mathematical method for this conversion will have errors and deformation, is reduced in accordance with the needs of different error arises various projection methods.

In accordance with deformation of the projection of divided:

(1) an isometric: equal angle in both directions and a projection plane in two directions on the field angle.

(2) equal area projection: the ratio of the area of ​​the region and the area of ​​the earth is fixed on the map.

(3) The projection: neither is an isometric nor equal area projection.

The configuration of side surfaces of the projection carrier divided:

(1), also known azimuthal projection plane, the projection projected on the earth's surface to a plane tangent to the earth's surface or secant to the sphere center viewpoint.

(2) a conical projection, secant or tangential to one of latitude of the earth, and the axis of the cone axis coincides with a cone, the sphere center of the projection surface of the earth to the viewpoint on the conical surface, cut along a generatrix of a cone to carry out a plane to form a map.

(3) Cylindrical projection may be considered as a special way conic projection, the bearing surface is a cylinder.

Commonly used map projection

(1) Gauss - Kruger projection ,

Conformal transverse cylindrical projection belonging envisaged with a cylindrical transverse to the central meridian of the sphere with the projection, the projection projector according to a straight line and the central meridian and equatorial projection of constant length condition straight, constant over the side of the central meridian difference in the range of spherical and conformal projection sphere and the cylindrical surface along a generatrix of the poles carry flat cut can be obtained of plane. Gauss projection central meridian and equatorial addition, other warp threads are symmetrical to the central meridian curve, Gauss projection angle no deformation, the deformation is very small area, and length, the central meridian without deformation, the deformation is gradually increased. Usually the projection 6 is divided in accordance with degrees or 3 degrees, 6 degrees divided band or band 3 degrees. With 6 degrees from the 0 degree meridian difference by 6 degrees starting from west to east dividing the globe is divided into 60 bands. 3 of the tape is divided in the base 6 of the belt on his central meridian and 6 of the central meridian and the sub-strip line zoning coincides, i.e., from 1.5 degrees brought up every 3 degree area, numbered from 1 to 120 degree belt.

(2) Mercator projection ,

Conformal cylindrical projection belonging to the tangent, assuming a standard hollow cylinder transverse to the surface of the ball equator, the imaginary center of the Earth There is a lamp, the shape of the projection surface of the earth with the cylindrical surface of the cylindrical surface is formed to expand a Mercator projection map . Mercator projection angle without distortion, a straight line is perpendicular to the latitude and longitude, latitude interval began to expand from the standard parallel to two. Mercator projection length and area maps significant deformation, but the standard parallel without deformation. Mercator map used for aeronautical charts and navigational charts. Map "national bathymetric charts norms" scale of less than 250 000 should adopt the reference latitude of 30 degrees Mercator projection.

(. 3) the UTM projection ,

Stands for Universal Transverse Mercator projection, the horizontal axis is an isometric cut cylindrical projection. Two standard parallels of latitude 80 degrees north latitude 84 degrees, the two standard parallels secant rear projection is not deformed, the central meridian length ratio of 0.9996. UTM projection similar to the projection Gaussian globe is divided into 60 with the projection, from west to east longitude banding from 180 degrees, 6 degrees per area. Our satellite imagery commonly used for this projection.

(4) Lambert projection ,

Conformal Conic projection belongs. Divided into two types, (1) Conformal Conic envisaged to cut a conical or spherical in cutting, application conditions isometric projected onto the conical surface of the earth, and then cut along a generatrix show conical surfaces planar. Projected weft of the concentric arcs, the radius of the warp threads are concentric. No angular distortion, warp and weft length equal to length ratio. For the production along the latitude distribution of mid-latitude regions, small-scale maps. With this projection prepared 1:100 10000 topographic maps and aeronautical charts internationally. ② equal area azimuthal projection. Spherical contemplated that a plane tangential to the point, like the product according to the conditions in the projection plane from latitude and longitude lines. Projection by the relative position of the Earth's surface is divided into positive axis, horizontal and diagonal axis three kinds. In the normal projection of the weft concentric, tapering outwardly spaced from the center of projection, the radius of concentric warp. The projection on the horizontal axis, the central meridian and equatorial line perpendicular to each other, the other warp and weft yarns are symmetrical to the curve of the central meridian and equatorial. In oblique projection, the central meridian is a straight line, other curve symmetrical to the warp threads of the central meridian. No deformation of the projection area, the angle and length of deformation increases from the center to the periphery projected. The horizontal axis oblique projection and projection applications more often, partial hemispheres and continents FIG FIGS multi projector.

How to convert projection

method 1

You can get to the beginning of a canvas in a projection inside gis, and then introduced into the other eleven.

Method 2

About shp projective transformation vector files: Element - Projection (Projection defined)

Method 3

Projection conversion on tif raster files: Grid - Project Raster

Method 4

View - attribute data frame

Method 5 (recommended)

As long as the spatial reference frame to re-output data re-introduced into it.

How to check geographic coordinate system

method 1

You can query each layer of "Layer Properties"

Method 2

View the properties of the entire layer, take a look at the favorites are not showing

Original link: https: //blog.csdn.net/devCopper/article/details/8496712