查找最近全球定位系统指向用户位置形成一个列表 [英] find nearest Gps point to the user location form a list
问题描述
我想做的事：用户选择，并开始在地图上目的地，然后从他们的坐标，我想说明从在地图上的位置列表中的最近点的位置。我有一个包含的可能位置的经度，纬度和名称的简单的SQLite数据库。
what i am trying to do: the user selects start and destination on a map and then from their coordinates i want to show the closest point location from a list of locations on map. i have a simple Sqlite database containing the longitude,latitude and name of the possible locations.
我做了一些研究，这是我发现了什么：
i did some research and this is what i found:
http://www.scribd.com/doc/ 2569355 /地理距离 - 搜索 - 与MySQL的
但这是为使用它与MySQL和某种空间搜索推广的。 是否有可能，我可以做同样的事情使用的Android API或外部库？
but this is meant for using it with mySql and some kind of spatial search extension. is there a possibility i can do something similar using android api or external libs?
public Point dialogFindClosestLocationToPoint(geometry.Point aStartPoint){
List<PointWithDistance> helperList=new ArrayList<PointWithDistance>();
try {
openDataBase();
Cursor c=getCursorQueryWithAllTheData();
if(c.moveToFirst())
do{
PointWithDistance helper=new PointWithDistance(c.getDouble(1),c.getDouble(2),c.getString(3));
int distance=returnDistanceBetween2Points(aStartPoint, helper);
if(distance<MAX_SEARCH_DISTANCE){
helper.setDistance(distance);
Log.i("values", helper.name);
helperList.add(helper);
}
}while (c.moveToNext());
Collections.sort(helperList,new PointComparator());
if(helperList!=null)
return helperList.get(0);
else return null;
}catch(SQLException sqle){
throw sqle;
}
finally{
close();
}
这是在code在PointComparator（）类：
this is the code in the PointComparator() class:
public int compare(PointWithDistance o1, PointWithDistance o2) {
return (o1.getDistance()<o2.getDistance() ? -1 : (o1.getDistance()==o2.getDistance() ? 0 : 1));
}
其中， PointWithDistance 是包含一个对象：土地增值税，长，距离远，名称
where PointWithDistance is a object that contains: lat, long , distance, name
但是这种解决方案并没有提供正确的返回信息...我意识到，这不正是可扩展性都非常缓慢。我需要将执行速度快与最高的1000行的数据库解决方案。
however this solution doesn't provide the right return info... and i realize that is it not scalable at all and very slow. i need a solution that will execute fast with a database with max of 1000 rows.
编辑：我有这个code在分类的错误，现在我把它改变了（应该是＆LT;代替>）
edit: my there was a mistake in this code in the sorting now i have it changed( should be < instead of >)
推荐答案
我一直在寻找的东西非常相似前段时间：
I was looking for something very similar some time ago:
<一个href="http://stackoverflow.com/questions/2034348/android-sqlite-sort-on-calculated-column-co-ordinates-distance">http://stackoverflow.com/questions/2034348/android-sqlite-sort-on-calculated-column-co-ordinates-distance
我是用我的服务器上一个MySQL查询，MySQL允许你创建一个虚拟列，进行计算和排序按距离，然后就可以设置最大结果返回或最大距离 - 它工作得很好：
I was using a MySQL lookup on my server, MySQL allows you to create a virtual column, performs the calculation and sorts by distance, and then you can set the max results returned or the max distance - it works very well:
Select Lat, Lon, acos(sin($lat)*sin(radians(Lat)) + cos($lat)*cos(radians(Lat))cos(radians(Lon)-$lon))$R As dist From MyTable ORDER BY dist DESC
我想执行相同的操作在我的应用程序 - 为了从用户的位置，让我展现最接近的人拉开距离拉所有的点。我结束了沿之一的线的解决方案建议去上面的链接，但实现它的可能不是最佳的解决方案，但适用于我想要的目的。
I wanted to perform the same operation in my app - pull all the points in order to distance from the users location allowing me to show the closest ones. I ended up going with the a solution along the lines of the one suggested on the link above but realise its probably not the optimal solution but works for the purpose I wanted.
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