How To Load Markers Dynamically For Current Position In Android Google-maps?
Solution 1:
You could use getMapCenter and just add or subtract the latitude span or longitude span (divided by 2 of course) to find the bounds.
Solution 2:
Where are those place-marks coming from? If they are coming from a web service, check if the web service supports spatial queries. If its a basic point in extent (rectangular envelope) you could do something like this:
Note: (xmin, ymin -> xmax, ymax) are the bounds of your rectangle (extent).
defis_point_in_rect(px, py, xmin, ymin, xmax, ymax):
if px >= xmin and px <= xmax:
if py >= ymin and py <= ymax:
returnTrueelse:
returnFalseThis is something very simple. You can even use the Google Maps Data API to store your place-marks and that has a mechanism to execute spatial queries.
If your data is on Google App Engine, then you could use GeoPt based queries or you could roll your own spatial index. Check out http://code.google.com/p/geomodel/
Solution 3:
I'm doing something similar to yourself but I'm using a server. The reason I'm doing so is for computational reasons. When the application first starts a HTTP request is sent to a php script which contains a MySQL query. The php script recieves the users current lat / long and gives back in a JSON all points within 1KM of the current location. The application then parses that JSON into a local MySQL database and does stuff with it.
To send the HTTP request and parse the JSON into a database I'm doing the following..
//http posttry{
HttpClienthttpclient=newDefaultHttpClient();
HttpPosthttppost=newHttpPost("http://URL");
httppost.setEntity(newUrlEncodedFormEntity(parameters));
HttpResponseresponse= httpclient.execute(httppost);
HttpEntityentity= response.getEntity();
InputStreamis= entity.getContent();
//convert response to stringBufferedReaderreader=newBufferedReader(newInputStreamReader(is,"iso-8859-1"),8);
StringBuildersb=newStringBuilder();
Stringline=null;
while ((line = reader.readLine()) != null) {
sb.append(line + "\n");
}
is.close();
result=sb.toString();
}catch(Exception e){
newAlertDialog.Builder(this)
.setTitle("Woops!")
.setMessage("Getlocations:It appears the server is not reachable. Check your connectivity and try again.")
.setPositiveButton("Ok", newDialogInterface.OnClickListener() {
publicvoidonClick(DialogInterface dialog,
int which) {
//User wants to start activity..
}
})
.show();
Log.e("log_tag", "Error in connection or convert "+e.toString());
}
//parse json datatry{
System.out.println("parsing data");
JSONArrayjArray=newJSONArray(result);
if(icount != 0){
try{
SQLiteDatabasedb= tweets.getWritableDatabase();
db.delete(TABLE_NAME,null,null);
}finally {
tweets.close();
}
}
//TODO: Change this to numfor(int i=0;i<jArray.length() && q < 1;i++){
System.out.println("ARRAY LENGTH " + jArray.length());
q++;
JSONObjectjson_data= jArray.getJSONObject(i);
System.out.println("Getting Info");
Doublelat= json_data.getDouble("lat");
Doublelng= json_data.getDouble("lng");
Stringlink= json_data.getString("link");
Stringmessage= json_data.getString("message");
Stringsname= json_data.getString("sname");
Stringname= json_data.getString("name");
//Add each entry to SQL database...
System.out.println("Adding table row!");
try{
addloc(name,sname,message,link,lat,lng);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
tweets.close();
}
count();
}
}catch(JSONException e){
newAlertDialog.Builder(this)
.setTitle("Woops!")
.setMessage("Getlocations: It appears something went wrong processing the information.")
.setPositiveButton("Ok", newDialogInterface.OnClickListener() {
publicvoidonClick(DialogInterface dialog,
int which) {
//User wants to start activity..
}
})
.show();
Log.e("log_tag", "Error parsing data "+e.toString());
}
For this to work all you need is a short php file which takes the Lat / lng Something like...
<?php
mysql_connect("host","user","pass");
mysql_select_db("database");
$lat = $_REQUEST['currlat'];
$lng = $_REQUEST['currlng'];
$q=mysql_query("QUERY") ordie(mysql_error());
if (mysql_num_rows($q) == 0) {
echo"No rows found, nothing to print so am exiting";
exit;
}
if(!q){
echo"NO RESULT";
exit;
}
while($e=mysql_fetch_assoc($q))
$output[]=$e;
print(json_encode($output));
mysql_close();
?>That'll take in the values and print results in JSON.
//edit: To get the lat / lng in the first place I'm using the GPS.
Hope this helps.
Solution 4:
The answer would depend on where your markers are coming from. Are they stored within the Android device itself or are they coming from a web server? Either way, if you need to represent thousands of locations symultaneously you might need to implement some form of clustering, which can be done on the client or on the server, if markers come from the web.
See, for example this server side clusterer (2 different versions):
http://maps.forum.nu/server_side_clusterer
http://maps.forum.nu/server_side_clusterer/index2.php
or a client side clusterer:
http://gmaps-utility-library.googlecode.com/svn/trunk/markerclusterer/1.0/
Another alternative would be to use custom tiles, (like Google does), but depending on your exact needs it may be overkill.
Post a Comment for "How To Load Markers Dynamically For Current Position In Android Google-maps?"