There is construction happening nearby, so I got a set of drawings to look at. To my surprise, the technical requirements included a Changsha right-hand coordinate system. I was curious about where "zero" was located, so I started experimenting. While there were some resources online (28°11′39″N, 112°57′39″E; another is 112°57′33″E, 28°13′45″N), they seemed to refer to several points, which were not very accurate. I decided to calculate it myself. However, this is a very complex geometric problem!
Although I studied mechanical engineering, interpreting diagrams was still very easy for me, and I could obtain the following information:
1. The land parcel I am referring to is located in the first quadrant of Changsha's Cartesian coordinate system.
2. The X-axis points north and the Y-axis points east in this coordinate system.
3) The Y-axis corresponds to longitude, and the X-axis corresponds to latitude.
Therefore, it can be inferred that this zero point is located approximately 45 km west and 104 km south of my position. To refine this further, I can use the two points on the map to calculate their latitude and longitude, then reverse-calculate the latitude and longitude of the zero point.
Let the intersection of Yumo Tang Road and De Run West Road be point A:
Changsha coordinates: Y=45348.351, X=104895.735
Latitude: 28.245859016875855° N, Longitude: 112.9471802146530° E
Let the center point of the intersection between Yuehua North Road and the unconstructed road be point B:
Changsha coordinates: Y=45154.142, X=104587.844
Latitude: 28.243066121362624° N, Longitude: 112.94530803276061° E
Calculate the precision ratio:
A → B: ΔY = 194.209, ΔX = 307.891
This results in i = △E / △Y = 0.00000964003673
This results in j = △N / △X = 0.00000907105279
Therefore, we found that the Earth's surface is not a perfect sphere (not).
In reality, it's simply recognizing the difference between spherical coordinates and Cartesian coordinates. To simplify calculations, I disregarded projection errors and considered X'O'Y' and E'O'N' to be part of a standard Cartesian coordinate system.
Therefore, O(N-X×i, E-Y×j) represents 27.29434426770940°N, 112.51002044543600°E
It's strange that we've traveled so far; we're almost at Nanyue...
Or perhaps the reason for choosing this location is that it makes it convenient to use building coordinates in Changsha, where all coordinates are positive values?
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