nodejs-初探-简单的判定位置是否在市区API

看来nodejs还是越来越火了,WordPress也用上了nodejs抛弃了php,虽然php7比php5的效率高了一倍,然而在node,java等静态语言面前,还是不值一提.当然php还是有他的好处,开发迅速,修改便捷,适宜于调用api做应用层.另外由于node的封装性较低,node可以操作很多较为低级的操作,做路由,代理,解析头是相当方便,再加他不错的执行效率,我觉得用node做一些计算密集和I/O密集的方面还是很不错的.下面就是工作中遇到的,要判定用户坐标是否在市区的一个API,使用了判定点是否在多边形内的算法,大概思想是对每条边,判断点与这条边起始点与测试点的矢量A,这条边顺时针方向的法矢量B,测定AB夹角,如果是锐角,说明在顺时针这一边,那么如果对所有边测试点都在同一边,那么他就是在此多边形内.要求多边形数据是凸多边形.代码:

//Import libraries
var fs = require('fs');
var http = require('http');
var url = require('url');

//To accelerate,save data in memory
var cityCenterAreas = [];

//Util functions
function Point(x,y)
{
return {x:x,y:y};
}

function Vector(p1,p2)
{
return {x:p2.x-p1.x,y:p2.y-p1.y};
}

function getNormalVector(v)
{
return {x:v.y,y:-v.x};
}

function dotMetrix(v1,v2)
{
return v1.x*v2.x + v1.y*v2.y;
}

function isInCloseWiseSide(checkPoint,vectorStart,vectorEnd)
{
var edge = Vector(vectorStart,vectorEnd);
var test = Vector(vectorStart,checkPoint);
var normalEgde = getNormalVector(edge);
return dotMetrix(test,normalEgde) > 0;
}

function isAcceptedCity(cityId)
{
return cityCenterAreas[cityId.toString()] != undefined;
}

/*
Algorithm contributer:Needle
*/

function isCityCenter(cityId,x,y)
{
if(!isAcceptedCity(cityId))return false;
var testPoint = Point(parseFloat(x),parseFloat(y));
cityId = cityId.toString();
var cityPointsNum = cityCenterAreas[cityId].length;
for(var i = 0;i < cityPointsNum;i++)
{
if(i != cityPointsNum - 1)
{
if(!isInCloseWiseSide(testPoint,cityCenterAreas[cityId][i],cityCenterAreas[cityId][i+1]))break;
}
else
{
if(!isInCloseWiseSide(testPoint,cityCenterAreas[cityId][i],cityCenterAreas[cityId][0]))break;
}
}
return i == cityPointsNum;
}

//Load data from file
fs.readFile('data.json',function(err,data)
{
if(err) throw err;
cityCenterAreas = JSON.parse(data);
//Data ready and start server
http.createServer(function(request,response)
{
var getParams = url.parse(request.url,true).query;
if(getParams.cityId == undefined || getParams.longitude == undefined || getParams.latitude == undefined)
{
response.writeHead(200,"Ok",{'Content-Type':'application/json'});
response.end(JSON.stringify({code:"-1",msg:"Params missing!"}));
}
else
{
var body = "";
response.writeHead(200,"Ok",{'Content-Type':'application/json'});
if(isCityCenter(getParams.cityId,getParams.longitude,getParams.latitude))
{
body = "true";
}
else
{
body = "false"
}
response.end(JSON.stringify({code:"0",msg:"Request OK!",body:body}));
}
}).listen(8888);
});

数据文件data.json 储存了多个城市市区的边界点:

{
"3":[{"x":120.205558,"y":30.389502},
{"x":120.277506,"y":30.353748},
{"x":120.340954,"y":30.328548},
{"x":120.369103,"y":30.248793},
{"x":120.229258,"y":30.10217},
{"x":120.152775,"y":30.127811},
{"x":120.113133,"y":30.140023},
{"x":120.065961,"y":30.212971},
{"x":120.052015,"y":30.274715},
{"x":120.089742,"y":30.376214}],
"2":[{"x":116.508855,"y":40.002653},
{"x":116.554975,"y":39.875276},
{"x":116.555488,"y":39.850388},
{"x":116.459083,"y":39.79315},
{"x":116.426467,"y":39.77228},
{"x":116.282473,"y":39.783381},
{"x":116.219807,"y":39.930934},
{"x":116.231881,"y":40.000832},
{"x":116.363346,"y":40.028867}],
"1":[{"x":121.415521,"y":31.402529},
{"x":121.703582,"y":31.29301},
{"x":121.785719,"y":31.127397},
{"x":121.6654,"y":30.911909},
{"x":121.273467,"y":30.889172},
{"x":121.16374,"y":31.005578},
{"x":121.145331,"y":31.137435},
{"x":121.15206,"y":31.201511},
{"x":121.212999,"y":31.346972},
{"x":121.225924,"y":31.351814}],
"4":[{"x":113.41212,"y":23.141401},
{"x":113.37996,"y":23.10377},
{"x":113.353711,"y":23.073766},
{"x":113.228603,"y":23.05616},
{"x":113.204727,"y":23.156197},
{"x":113.228603,"y":23.05616},
{"x":113.410747,"y":23.145397}]
}