我是 javascript 新手，正在使用 google maps API for javascript。
这是学校的任务，我们获得了一个工作脚本和一些 php 代码来显示地图、获取位置、更新位置等。
我们的任务是实现一个凸包算法。
这些是我遇到的问题：
- 一些对象的数据结构
- 计算完船体线后如何在地图上显示它们
这是代码；
function convexHull(){
console.log("convexHull()");
console.log(obj.length);
//check if there are more than one user, otherwise convex hull calculation would be useless
if(obj.length > 0){
//lists with x-positions and y-positions
var pos_x = [];
var pos_y = [];
//fill the lists
for(var i = 0;i < obj.length; i++){
pos_y.push(parseFloat(obj[i][1]));
pos_x.push(parseFloat(obj[i][2]));
console.log("point " + i + ": lat = " + pos_y[i] + ", lon = " + pos_x[i]);
}
//find lowest point index
var low_index = 0
for(var i = 1;i < obj.length; i++){
if(pos_y[i] < pos_y[low_index]){
low_index = i
}
}
var angle_list = []
//make list of angles linked to index, the lowest point will not be in this list
for(var i = 0;i < obj.length; i++){
if(i != low_index){
var opos = pos_y[i] - pos_y[low_index];
var adj = pos_x[i] - pos_x[low_index];
//opos will always be positive, since the point with index low_index is the lowest point
if(adj > 0){
var new_angle = Math.atan(opos/adj);
var list_item = {index:i, angle:new_angle};
angle_list.push(list_item);
}
if(adj < 0){
var new_angle = Math.atan(opos/adj)+ Math.PI;
var list_item = {index:i, angle:new_angle};
angle_list.push(list_item);
}
if(adj == 0){ //if adj = 0, angle is 90 degrees
var new_angle = 90;
var list_item = {index:i, angle:new_angle};
angle_list.push(list_item);
}
}
}
//sort angle_list by ascending angles
angle_list = angle_list.sort(function(a,b){return a.angle - b.angle;});
for(var i=0;i< angle_list.length;i++){
console.log("angle = " + angle_list[i].angle + ", index = " + angle_list[i].index);
}
//GRAHAM ALGORITHM STARTS HERE
//this list will hold all indexes of convex points
var final_list = [];
//put the lowest point in the angle_list
var list_item = {index:low_index, angle:0};
angle_list.unshift(list_item);
//NEW STUFF HERE
//eerst het beginpunt met laagste y-coor invoegen
//english: inserting the starting point [lowest y coordinate]
final_list.unshift(angle_list[0]);
for(var i=2;i<angle_list.length;i++){
var value = (((pos_x[angle_list[i-1].index]-pos_x[angle_list[i-2].index])*(pos_y[angle_list[(i)].index]-pos_y[angle_list[i-2].index]))-((pos_y[angle_list[i-1].index]-pos_y[angle_list[i-2].index])*(pos_x[angle_list[(i)].index]-pos_x[angle_list[i-2].index])));
//left turn, this is good
if(value > 0){
console.log("left turn");
final_list.push(angle_list[i-1]);
}
//right turn, this is not good
if(value < 0){
console.log("right turn");
continue;
}
//points lie on a line
if(value == 0){
final_list.push(angle_list[i-1]);
console.log("colinear");
}
}
}
setTimeout(function(){convexHull();}, 5000);
console.log(final_list);//this is what the console outputs: [Object, Object, Object, Object, Object] I don't understand why it has this structure!
return final_list;
}
function DrawHull(final_list){
for(var i = 0; i < final_list.length-1; i++){
console.log(parseFloat(obj[final_list[i]]));
var p1 = new L.LatLng(parseFloat(obj[final_list[i]][1]),parseFloat(obj[final_list[i]][2]));
var p2 = new L.LatLng(parseFloat(obj[final_list[i+1]][1]),parseFloat(obj[final_list[i+1]][2]));
var pointList = [p1, p2];
polylines.push(new L.polyline(pointList, {
color: 'yellow',
weight: 10,
opacity: 0.5,
smoothFactor: 1
}).addTo(mymap));
}
}
我的主要看起来像这样；
getLocation();
var mymap = L.map('mapid').setView([51.0336851,3.7019778], 13);
L.tileLayer('https://api.tiles.mapbox.com/v4/{id}/{z}/{x}/{y}.png?access_token={accessToken}', {
attribution: 'Map data © <a href="http://openstreetmap.org">OpenStreetMap</a> contributors, <a href="http://creativecommons.org/licenses/by-sa/2.0/">CC-BY-SA</a>, Imagery © <a href="http://mapbox.com">Mapbox</a>',
maxZoom: 18,
id: 'mapbox.streets',
accessToken: //I deleted this, I figured it should stay private
}).addTo(mymap);
DrawHull(convexHull()); //These two funcions and this line are the only things I wrote with my classmate [and his code is based on some code he found on the web and adjusted to our needs]
基本上我首先想知道的是为什么 var final_list 有一个结构 [Object, Object, Object, Object, Object] （控制台输出的内容）
因为我收到此错误： Uncaught TypeError: Cannot read property 'length' of undefined at DrawHull
我认为我以正确的方式实现了该算法，但我无法对其进行测试。
如果您需要更多信息，请不要犹豫，也欢迎提出如何使这个问题变得更好的提示[这是我的第一个问题！因此，请考虑到这一点，并在提供建设性反馈的同时保持友善]