Can you see the difference between 54 coordinates and 80 coordinates?

I can't see this. For example, when GPS data is collected in the field, the data is represented in geodetic coordinates, that is, latitude, longitude and elevation. In order to display the collected data on the map, it is necessary to convert the latitude and longitude into plane coordinates, which are commonly referred to as x,y coordinates.

Because China's topographic maps generally use Gaussian projection, they are usually converted into Gaussian plane coordinates and displayed on the map. In the process of converting latitude and longitude to plane coordinates, ellipsoid parameters need to be used, so the selected coordinate system should be considered, the coordinate systems commonly used in China are Beijing 54, Xi'an 80, WGS-84 coordinate system, the ellipsoid corresponding to different coordinate systems is different, here you may not understand what the relationship between the root ellipsoid is, it is like this, the geographic data we are talking about are to describe a point on the geid, and the geoid is irregular, We use a prescribed ellipsoid to fit this level, and use the points on the ellipsoid surface to approximate the points on the earth. Each country has different geographical conditions and uses different ellipsoids.

The Beijing 54 coordinate system uses the Krasovsky ellipsoid, while the Xi'an 80 uses the IAG 75 earth ellipsoid.

The difference is very small" is also not true, theoretically the correction amount of the two different locations is not the same, sometimes large and sometimes small, but the drawing is indeed to select a common correction amount, the topographic map from Beijing 54 coordinate system to Xi'an 80 coordinate system should be carried out on the Gaussian plane, the old and new ellipsoid parameters are different, the position of the center is also different, the vertical and horizontal axis does not coincide in the Gaussian plane, so each point on the topographic map has a difference in the two coordinate systems x, y. The conversion of the 54-coordinate topographic map of Beijing to the 80-coordinate topographic map of Xi'an is to find the difference between the Gaussian plane coordinates of the old and new coordinate systems of the mapping control points on each old map, that is, the correction amount. Through the calculation and statistics of thousands of first- and second-class locations in China's 1.1 million topographic maps, it is proved that only one control point Gaussian plane coordinate correction is calculated for each map as the public correction of the whole map.

However, most of the GIS projects in China use a scale greater than 1 100,000 to build a library, so each piece can be used to select a point to calculate the correction of the Gaussian plane as the public correction of the map sheet for new topographic map conversion.

Give you a 54 Beijing coordinates 80 Xi'an coordinates calculation and belt change program:

Calculated by hand.

A detailed understanding of the coordinate conversion problem is important for measurement, so please discuss this with me.

First, we're going to figure out a couple of coordinate representations. There are roughly three ways to represent coordinates: latitude, longitude and elevation, spatial Cartesian coordinates, planar coordinates, and elevation.

The WGS-84 coordinates we usually talk about are latitude and longitude and elevation, and the Beijing 54 coordinates are plane coordinates and elevations.

Now, let's figure out the tightness of the conversion, the conversions in the same ellipsoid are all tight, and the conversions between different ellipsoids are not tight. For example, there is no set of conversion parameters between WGS-84 coordinates and Beijing 54 coordinates that can be used across the country, and it will be different in each place, because they are two different ellipsoidal datums.

So, what should the coordinate conversion between two ellipsoids look like? Generally speaking, the seven-parameter method is used strictly, i.e., x translation, y translation, z translation, x rotation, y rotation, z rotation, and scale change k. If the area is not large, the distance between the farthest points is not more than 30km (empirical value), which can be used with three parameters, that is, x translation, y translation, z translation, and x rotation, y rotation, z rotation, and scale change k are regarded as 0, so the three parameters are only a special case of seven parameters.

The software provides the function of calculating three parameters and seven parameters. For example, in Shenzhen, there are both Beijing 54 coordinates and Shenzhen coordinates, and four parameters are used to convert between these two coordinates, and two known points are required to calculate the four parameters. This software provides the function of calculating four parameters.

Explain it clearly!

Oh, I don't know to look at the answer.

In China, there are three sets of coordinate systems, one is the Beijing 54 coordinate system.

The second is the Xi'an 80 coordinate system.

The third is the WGS-84 coordinate system, of which the first two are the most common. The difference between 54 and 80 coordinates is actually due to the ellipsoid chosen.

The benchmark is not the same. The Krasovsky ellipsoid is the ellipsoidal datum used in the Beijing 54 coordinate system, while the Xi'an 80 coordinate system uses the IAG-75 earth ellipsoid model, and the accuracy of the two coordinate systems in different regions.

There are also differences.

The difference in the coordinate system actually comes from the different choice of ellipsoidal datum, the earth can be approximated as an ellipsoid, so the value of the major semiaxis and the flattening ratio estimated for this ellipsoid is different, and the coordinate system obtained under these two sets of data will naturally be different. The Krasovsky ellipsoid is the ellipsoidal datum used in the Beijing 54 coordinate system, while the IAG-75 earth ellipsoid model is selected for the Xi'an 80 coordinate system, and the accuracy of the two coordinate systems is also different in different regions.

The Beijing 54 coordinate system uses the basic parameters of the Earth's ellipsoid, which is in contact with the former Soviet Union.

Under the conditions of joint measurement, the Krasovsky ellipsoid model was modified to a certain extent, and the parameters obtained by local adjustment were as follows: the value of the major semi-axis is a kilometer, the value of the minor semi-axis is a kilometer, and the value of the flattening ratio is 1.

The parameters of the earth ellipsoid adopted in the Xi'an 80 coordinate system are the origin of the earth at the 16th Congress of the International Union of Geodesy and Geophysics.

It is located in Jingyang County, Shaanxi Province, China.

According to the data obtained by Yongle Town, the measured parameters are: the value of the major semi-axis is kilometers, the value of the minor semi-axis is kilometers, and the value of the flattening ratio is 1.

Because the ellipsoid datum is different, the accuracy of adaptation to each region is also different, if you need to convert the two, the workload is too large for manual work, but the known points can be automatically converted through GPS software joint testing.

Geodetic coordinates (BLH) versus planar Cartesian coordinates (xyz).

The conventional conversion should first determine the conversion parameters, that is, the ellipsoid parameter, the zoning criterion (3 degrees, 6 degrees) and the longitude of the **meridian. The ellipsoid parameter refers to what kind of ellipsoid datum is used in the plane Cartesian coordinate system, which corresponds to different major and minor axes and flattening ratios. In general engineering, the 3rd degree zone is widely used.

There are two ways to determine the **meridian, one is to take the first two digits of the Y coordinate in the plane Cartesian coordinate system*3, and the longitude of the corresponding **meridian can be obtained. For example, x=3250212m, y=395121123m, then the longitude of the **meridian = 39*3=117 degrees. Another method is according to the geodetic coordinates longitude, if the longitude is between degrees, then the longitude of the corresponding **meridian = (degrees, in other cases you can infer 3 degrees according to this.

Conversion of any two spatial coordinate systems.

Since the survey coordinate system and the construction coordinate system use different standards, it is necessary to know at least 3 coincident points (i.e., points where the coordinates are known in both coordinate systems) in order to make an accurate conversion. The Bursha model is used to solve the problem. Bulsha formula:

Transform the equation equivalence to yield:

To solve these seven parameters, at least three known points (the coordinates of both coordinate systems are known) are used, and the indirect adjustment model is used to solve them

Where: v is the residual matrix;

x is an unknown seven-parameter parameter;

a is the coefficient matrix;

Solution: l is the closure difference.

After solving the seven parameters, you can use the Bursa formula to convert the coordinates of unknown points, and each time you input a set of coordinate values, you can find its coordinates in the new coordinate system. However, in order for GPS observations to be used in engineering or surveying, it is also necessary to convert local Cartesian coordinates to geodetic coordinates, and finally to plane Gaussian coordinates.

The above method is similar to our indirect adjustment, which is more complex to solve, and the following provides a coordinate conversion program, which can solve the seven parameters of the coordinate transformation by simply entering the coordinates of three known points. If the number of known points is large, the adjustment between parameters can be performed, and the accuracy is higher.

When the number of known points is only two, we can use the simple transformation method, which is more convenient and easy to do, and is suitable for manual calculation, but the accuracy is limited.

The detailed equation is as follows:

The middle notes of x, y, and x'、y\'Old and new respectively (or; The coordinates of the coincident points of the old and new) nets, a, b, and k are the transformation parameters, and obviously to solve a, b, and k, there must be at least two coincident points, and four equations are listed.

The usual parameter adjustment can be carried out to solve the values of a, x, b, c, and d parameters. Replace it with equation (3), the residuals (correction number) of each fitting point can be obtained by equation (2), and the coordinates of the point to be replaced can be obtained.

After the calculation parameters are calculated, the rest of the coordinates can be converted in Excel.