First, let’s talk about the origin and development of the latitude-longitude coordinate system. In fact, the purpose is very simple to represent our earth and the world in a digital way.
In the true sense of the coordinate system related to webgis, we have to talk about the wgs84 coordinate system first. This is a set of coordinate system proposed by Laomei in 1984. Therefore, it is named as 84 coordinate system. The 84 coordinate system is currently a widely used coordinate system, but it is not the earliest coordinate system. Before him, there were many coordinate systems. For example, Mercator was invented as early as 1512, but the technical level at that time could not abstract the earth as a three-dimensional sphere. Just hand-drawn the map into a square.
WGS84 is the earliest and more comprehensive coordinate system that uses various means such as equipment measurement, theoretical derivation, and field exploration. Its construction method is relatively comprehensive, combining multiple observation stations, transforming based on a fixed reference system, and integrating
data from GPS monitoring stations. So the accuracy is still very high. This is one of the reasons why it can still be used today.
How is the wgs84 coordinate system formed? The first is to abstract the earth into an ellipsoid, so we should simply know the mathematical parameters of the ellipsoid. There are two key parameters, the semi-major axis and the semi-minor axis. Just like an ellipse (isn't an ellipse an ellipsoid if it rotates once?) So the basis of the wgs84 coordinate system is to accurately measure the earth's semi-major axis and semi-minor axis. We all know that the earth is a two-level "oblate sphere" slightly flattened by the equator and slightly longer, so its semi-major axis should be the radius of the circular surface where the equator is located, and its semi-minor axis is the distance from the center of the earth to the North and South Poles. All these calculations are based on our imagination of the earth as a standard ellipsoid.
So is there any problem with such an abstraction? Can the ellipsoid really accurately express the position information of our earth? The answer is yes. Even though our earth is not a standard ellipsoid, the surface is full of bumps, high and low, mountains and seas, it looks extremely non-standard, and the previous rendering looks like this: