Recently, there has been a new situation of epidemic situation in many parts of the country, and the situation of prevention and control is still grim.
At the same time, the new terms "space-time accompaniment" and "space-time companion" also came into being.
To be honest, the first time I heard this word, it was really full of sci-fi, as if I had crossed into the future world.
Space-time companion refers to the fact that the person's telephone number and the confirmed number stay together in the same space-time grid (the range is 800m*800m) for more than 10 minutes, and the cumulative stay time of either party number in the past 14 days exceeds 30 hours, and the number found is a space-time companion number. My green health code will become a yellow code with a warning nature, and will be marked by the system as "Space-time Companion".
(Source: Red Star News Network)
It's a word that's both romantic and rigorous.
But it also made me wonder. The advance statement is not a question about the epidemic prevention measures, but only some points that I am curious about, so I am shallow and have to ask questions.
We can clearly see that the reported dwell range is 800 multiplied by 800, which is obviously a square method of calculating the area.
But shouldn't the important thing be the distance of 800 meters? We know that to better represent the distance of 800 meters, there is a better tool mathematically than a square, that is, a circle.
Any point on the circle is equally distanced to the center of the circle.
Including the coverage of our search base station, the concept map presented is also in the form of a circle.
So why are you delineated by squares?
Friends who are better at mathematics know that the farthest distance between the two points in the square (diagonal) can be calculated by multiplying 800 by the root number 2, accurate to two decimal places, which is about equal to 1131.37 meters, which has exceeded one-third of 800 meters, and the gap is not insignificant.
According to the idea of our little people, perhaps the square calculation is more convenient after the grid division, and the big data algorithm is also more convenient, so there is no round algorithm. As for whether this is the case, we don't know, just a personal guess.
Everyone is familiar with the positioning system is GPS, but even if it is GPS, it is not enough in the accuracy of positioning, and there will be errors.
When I drive a car on the road, the navigation only tells me where to go and doesn't determine which lane I'm in. (Maybe it's possible to locate so precisely, but it's not necessary for individuals to be so precise?) ）
However, as a positioning technology, base station positioning inevitably has the problem of error. The positioning accuracy of the base station depends on the distribution density of the base station. Densely populated bustling urban base stations are densely distributed, the positioning accuracy is higher, and there is also an error, that is, the remote villages with relatively small populations, the density of base stations is weak, is the error larger?
I once went to a remote farm, because the signal was not good, I almost couldn't use mobile payment.
Since there is an error, there are inevitably people who are "located" wrong, even if it is only a very small number, so how can these people prove that they have been to a certain place and have not been to a certain place? Big data determines that you have gone somewhere, how do you prove that you have not been? It's a profound technical question.
Just now we mentioned the example of GPS, saying that GPS can't tell which lane you're in. At the same time, the ground is not always flat, and friends who often drive also know that gps is equally difficult to grasp the judgment of height.
It is not clear whether the car is on the overpass or the passage under the bridge; it is not clear whether it is driving on the ground or wandering around in the underground garage.
So can the base station solve the height problem of positioning? If so, should the range of judgment change from a square of 800 × 800 to a cube of 800×800×800?
If not, is it possible for two people who are less than 800 meters apart in horizontal distance to be greater than 800 meters in a straight line?
Strictly speaking, 800-meter tall buildings are really rare, but 800 meters above sea level can indeed be reached, especially for some mountainous hilly landforms, and uneven heights and lows in short distances are also common. How can this be determined?
In fact, I also saw some questions raised by netizens, such as:
Since the definition of a space-time companion is "either party", if one of them is outside and the other party is already in home isolation, is it still counted?
If the mobile phone is lost and the time and space movement caused by being picked up, is it also counted on your own head?
……
Or strengthen exercise, improve immunity, do a good job of personal protection, do what you can!