在mysql中计算哪些点（纬度，经度）在一定距离内？ [英] Computing which points (latitude, longitude) are within a certain distance in mysql?

问题描述

有两点A，B和距离x（距离A的距离）和y（距离B的距离）。让从A到B的距离为N.因此，A距离B为N英里。我该如何解决问题：距离A有（N + x + y）英里的可用点数是多少？我不确定如何更好地解释这一点。我真的不知道如何解决这个问题，我阅读了

There are two points A, B, and distances x (miles from A), and y (miles from B). Let the distance from A to B be N. So, A is N miles away from B. How do I solve the problem: What are the points available that are (N + x + y) miles away from A? I'm not sure how to explain this any better. I really have no clue on how to attack this problem, I read Fastest Way to Find Distance Between Two Lat/Long Points and I believe the solution given calculates the distance between two points and have no idea if this solution could be used to apply to my problem, or if so, how.

解决方案

If you are looking for an approximation algorithm I suggest to look for a k-means algorithm or a hierarchical cluster, especially a monster curve or a space filling curve. First off you can compute a minimal spanning tree of the graph and then remove the longest and expensivest edges. Then the tree makes many little trees and you can use the k-means to compute group of points i.e. clusters.

"The single-link k-clustering algorithm ... is precisely Kruskal's algorithm ... equivalent to finding an MST and deleting the k-1 most expensive edges." See for example here: https://stats.stackexchange.com/questions/1475/visualization-software-for-clustering.

A good example for a monster curve is the hilbert curve. The basic form of this curve is an U-shape and by copy many of it together and rotating it the curve fills the euklidian space. Surprisingly a gray code can help to find out the orientation of this U-shape. You can look up Nick's spatial index quadtree hilbert curve blog article about more details. Instead to calculate the curve's index you can put together a quadkey like in bing maps. The quadkey is unique for each coordinate and it can be used with normal string operations. Each position in the key is part of the U-shape curve and thus you can select this region of points from select partially from left to right from the quadkey.

In this image you can see the green polygon is found using a hilbert curve:

You can find my php classes here: http://www.phpclasses.org/package/6202-PHP-Generate-points-of-an-Hilbert-curve.html

这篇关于在mysql中计算哪些点（纬度，经度）在一定距离内？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！