Introduction
Station-centered coordinate system, geocentric coordinate system, geocentric coordinate system, Web Mercator projection coordinate system, pixel coordinate system, tile coordinate system
1. Spherical coordinate system
1.1 Geocentric geofixed coordinate system ECEF
Coordinate system definition: Taking the center of mass of the earth as the coordinate origin, the z-axis points to the pole, the x-axis passes through the intersection of the equator and the prime meridian, and the y-axis completes the right-handed coordinate system.
Coordinate format: [x,y,z], unit m
1.2 Station center coordinate system ENU
Coordinate system definition: The station center coordinate system is the northeast sky coordinate system, with the user's position P as the origin of the coordinates, the z-axis points to the sky, the x-axis points to the east, and the y-axis points to the east north.
Coordinate format: [x,y,z], unit m
1.3 Geocentric coordinate system WGS84
can be approximately regarded as the same as the geocentric fixed coordinate system ECEF, with the geocenter as the coordinate origin, the x-axis points to the intersection of the plane where the 0-degree radial line is and the equator, and the y-axis completes the right-handed coordinate system. WGS84 is used for GPS navigation.
Coordinate format: [经度，维度，高度], unit degree
2. Projection plane coordinate system
2.1Web Mercator projection coordinate system
Coordinate system definition:
Taking the entire world, the equator is used as the standard latitude, the prime meridian is used as the central meridian, the intersection of the two is the origin of the coordinates, east and north are positive, and direction is positive. West to south is negative.
Coordinate system projection process:
The Mercator projection, also known as the "equiangular cylindrical projection", was formulated by the Dutch cartographer Mercator in 1569. It is assumed that the earth is enclosed in a hollow cylinder, and its equator is in contact with the cylinder. Contact, and then imagine that there is a light in the center of the earth, project the graphics on the sphere onto the cylinder, and then unfold the cylinder. This is a "Mercator projection" with the standard latitude being zero degrees (that is, the equator). world map.
Sitting format: [x,y]，单位m
2.2UTM coordinate system
Coordinate definition:
The UTM coordinate system refers to the Universal Transverse Mercator grid system. The UTM projection is an elliptical cylinder cutting the earth's ellipsoid with the transverse positive axis. The center line of the elliptical cylinder is located in the ellipse. On the equatorial plane of the sphere and passing through the ellipsoid mass point. Thus the points on the ellipsoid are projected onto the elliptical cylinder.
UTM projection distribution zone:
The UTM longitude zone ranges from 1 to 60, of which 58 zones span 6° from east to west. The longitude zone covers all of the Earth's mid-latitude range from 80°S to 84°N. There are 20 UTM latitude zones, each spanning 8° north to south; identified by the letters C through X (without the letters I and O). Areas A, B, Y, and Z are not within the scope of the system and cover the Antarctic and Arctic regions.
UTM coordinate representation:
The representation format of UTM coordinates is: east to north of longitude zone and latitude zone, where east represents the projection distance from the central meridian of the longitude zone, and North represents the projected distance from the equator. Both values are in meters. For example, using UTM to represent longitude/latitude coordinates 61.44, 25.40 results in 35V 414668 6812844; while using UTM to represent longitude/latitude coordinates -47.04, -73.48 results in 18G 615471 4789269. ,
3. Pixel plane coordinate system
3.1 Image plane coordinate system
When using laser point cloud information to create a reflectance base map, it is generally converted into a top view. It is usually necessary to set a resolution res, which means that a voxel of size res*res in the laser point cloud map corresponds to a pixel unit on the plane.
The image plane coordinate system is the ordinary pixel coordinate system in SLAM. The coordinate origin is located at the fixed point in the upper left corner of the image, the x-axis is to the right, and the y-axis is downward.
3.2 Tile map coordinate system
A tile image is a pixel block obtained by cutting an image into several grids according to a fixed size.