What I want to do is calculate a circle's radius by which the user is viewing the map.
I've written the solution so far as follows (which is true):
mMap.setOnCameraChangeListener(new GoogleMap.OnCameraChangeListener() {
#Override
public void onCameraChange(CameraPosition cameraPosition) {
String TAG = AppController.TAG;
LatLngBounds bounds = mMap.getProjection().getVisibleRegion().latLngBounds;
LatLng target = cameraPosition.target;
LatLng northEast = bounds.northeast;
LatLng southEast = bounds.southwest;
float[] results1 = new float[1];
float[] results2 = new float[1];
Location.distanceBetween(target.latitude, target.longitude, northEast.latitude, northEast.longitude, results1);
Location.distanceBetween(target.latitude, target.longitude, southEast.latitude, southEast.longitude, results2);
double distance = results1[0] > results2[0] ? results1[0] : results2[0];
Log.d(TAG, "onCameraChange:" + results1[0] + " " + results2[0]);
}
});
I'm facing two questions here:
1- First of all why the distane between the center and north east isn't equal to south west?
2- Is there any built in method to achieve the same result?
as you can see from the map above, the horizontal line (latitude) gets shorter the further away you get from the equator.
on the screen, the map is 'distorted' to flatten the curved surface of the earth, with +/- the same amount of longitude and latitude from the center of the view.
so unless you are taking measurements directly at the equator, you will have slight differences in the radius. for small distances, this is negligible.
if accuracy is not important, you can try using the smaller radius (if you want to draw a circle on the view that will not be partially hidden), or use the bigger radius (if you want to do calculations for places within that cicle).
I have a MapView called mMapView. I want to add a point graphic to the map. Here is what I did:
Point p1 = new Point(66.9969, 6.65428); //I took this coordinate from my GPS device for demonstration
Point p2 = (Point) GeometryEngine.project(
p1,
SpatialReference.create(4326),
mMapView.getSpatialReference());
Graphic graphic = new Graphic(
p2,
new SimpleMarkerSymbol(Color.RED, 10, SimpleMarkerSymbol.STYLE.DIAMOND));
mGraphicsLayer.addGraphic(graphic);//mGraphicsLayer is my GraphicsLayer on my MapView
When I ran my program the marker was not there on my MapView. But when I replaced mMapView.getSpatialReference() with SpatialReference.create(32637) the graphic appeared in exactly the right position I wanted. Why this is happening? I checked my MapView spatial reference id and latestid and and it is 102100 and 3857 respectively.
My guess is that the map doesn't yet have its spatial reference when you call project. It's hard to say because you didn't say where in the app your code snippet is. But if you put it in your Activity's onCreate method, the map's spatial reference is probably null still. Try an OnStatusChangedListener, like this:
mMapView.setOnStatusChangedListener(new OnStatusChangedListener() {
public void onStatusChanged(Object source, STATUS status) {
if (STATUS.INITIALIZED.equals(status)) {
mGraphicsLayer = new GraphicsLayer();
mMapView.addLayer(mGraphicsLayer);
Point p1 = new Point(66.9969, 6.65428);
Point p2 = (Point) GeometryEngine.project(
p1,
SpatialReference.create(4326),
mMapView.getSpatialReference());
Graphic graphic = new Graphic(
p2,
new SimpleMarkerSymbol(Color.RED, 10, SimpleMarkerSymbol.STYLE.DIAMOND));
mGraphicsLayer.addGraphic(graphic);
}
}
});
Another possibility is that your coordinates are not in latitude and longitude. As written, with lon = 66.9969 and lat = 6.65428, it should be in the ocean near India. If you meant lon = 6.65428 and lat = 66.9969, it would be in the ocean near Norway. If you didn't mean either of those locations, then your coordinates are either incorrect or not in latitude and longitude.
I'm using the computeOffset() from the SpericalUtil in the google maps android library. The computeOffset takes the parameters:
public static LatLng computeOffset(LatLng from, double distance, double heading)
with the original coordinates of the first two markers I can use the computeOffset to generate another line after inputing the distance and the heading. My goal is to make parallel lines at a certain distance apart. But as you can see below it looks pretty good when the lines are nearly north and south, but when you go towards east and west it looks to me like the distance between the two lines isn't the same value. The end points appear to be the right distance but offset. How can I make it so all the lines look like the first image no matter what direction?
public void onMarkerDragEnd(Marker marker) {
showDistance();
LatLng markerCPosition = SphericalUtil.computeOffset(mMarkerA.getPosition(), 50, 90);
mMarkerC = getMap().addMarker(new MarkerOptions().position(markerCPosition).draggable(true).visible(false));
LatLng markerDPosition = SphericalUtil.computeOffset(mMarkerB.getPosition(), 50, 90);
mMarkerD = getMap().addMarker(new MarkerOptions().position(markerDPosition).draggable(true).visible(false));
updatePolyline();
}
At the moment you're just shifting the points sideways using a constant angle (90 degrees). If I understand you correctly and you want both lines parallel to each other separated by some distance you need to take into account the heading of the original A-B line like so:
double heading = SphericalUtil.computeHeading(posA, posB);
LatLng markerCPosition = SphericalUtil.computeOffset(posA, 50, heading + 90);
LatLng markerDPosition = SphericalUtil.computeOffset(posB, 50, heading + 90);
I am trying to solve a problem with drawing a path from huge (100k+) set of GeoPoints to a MapView on Android.
Firstly I would like to say, I searched through StackOverflow a lot and haven't found an answer.The bottleneck of my code is not actually drawing into canvas, but Projection.toPixels(GeoPoint, Point) or Rect.contains(point.x, point.y) method..I am skipping points not visible on screen and also displaying only every nth point according to current zoom-level. When the map is zoomed-in I want to display as accurate path as possible so I skipping zero (or nearly to zero) points, so that when finding visible points I need to call the projection method for every single point in the collection. And that is what really takes a lot of time (not seconds, but map panning is not fluid and I am not testing it on HTC Wildfire:)). I tried caching calculated points, but since points be recalculated after every map pan/zoom it haven't helped
at all.
I thought about usage of some kind of prune and search algorithm instead of iterate the array, but I figured out the input data is not sorted (I can't throw away any branch stacked between two invisible points). That could I possible solve with simple sort at the beginning, but I am still not sure even the logarithmic count of getProjection() and Rect.contains(point.x, point.y) calls instead of linear would solve the performance problem.
Bellow is my current code. Please help me if you know how to make this better. Thanks a lot!
public void drawPath(MapView mv, Canvas canvas) {
displayed = false;
tmpPath.reset();
int zoomLevel = mapView.getZoomLevel();
int skippedPoints = (int) Math.pow(2, (Math.max((19 - zoomLevel), 0)));
int mPointsSize = mPoints.size();
int mPointsLastIndex = mPointsSize - 1;
int stop = mPointsLastIndex - skippedPoints;
mapView.getDrawingRect(currentMapBoundsRect);
Projection projection = mv.getProjection();
for (int i = 0; i < mPointsSize; i += skippedPoints) {
if (i > stop) {
break;
}
//HERE IS THE PROBLEM I THINK - THIS METHOD AND THE IF CONDITION BELOW
projection.toPixels(mPoints.get(i), point);
if (currentMapBoundsRect.contains(point.x, point.y)) {
if (!displayed) {
Point tmpPoint = new Point();
projection.toPixels(mPoints.get(Math.max(i - 1, 0)),
tmpPoint);
tmpPath.moveTo(tmpPoint.x, tmpPoint.y);
tmpPath.lineTo(point.x, point.y);
displayed = true;
} else {
tmpPath.lineTo(point.x, point.y);
}
} else if (displayed) {
tmpPath.lineTo(point.x, point.y);
displayed = false;
}
}
canvas.drawPath(tmpPath, this.pathPaint);
}
So I figured out how to make it all much faster!
I will post it here, somebody could possibly found it useful in the future.
It has emerged that usage of projection.toPixels() can really harm application performance. So I figured out that way better than take every single GeoPoint, convert it to Point and then check if it is contained in map viewport is, when I count actuall viewport radius of the map as following:
mapView.getGlobalVisibleRect(currentMapBoundsRect);
GeoPoint point1 = projection.fromPixels(currentMapBoundsRect.centerX(), currentMapBoundsRect.centerY());
GeoPoint point2 = projection.fromPixels(currentMapBoundsRect.left, currentMapBoundsRect.top);
float[] results2 = new float[3];
Location.distanceBetween(point1.getLatitudeE6()/1E6, point1.getLongitudeE6()/1E6, point2.getLatitudeE6()/1E6, point2.getLongitudeE6()/1E6, results2);
The radius is in results2[0]..
Then I can take every single GeoPoint and count the distance between it and the center of the map mapView.getMapCenter(). Then I can compare the radius with computed distance and decide whether ot not diplay the point.
So that's it, hope It will be helpful.
So I have a MapView with a lot of markers, most of which are concentrated in mile wide clusters. When zoomed the markers overlap and appear to only be one. What I want to achieve is at a certain zoom level replace the overlapping markers with a group marker that will display the density of markers and onClick will zoom to display all markers inside. I know I can do this with brute force distance measurements but there must be a more efficient way. Anyone have any solution or smart algorithms on how I can achieve this?
Um... assuming the markers are not grouped, layered or anything: why - before showing them - don't you create a grid of certain density and simply bin the markers into the cells of your grid?
If you then count that several markers fall into the same bin (grid cell) - you can group them. If you need slightly more clever grouping, you might also check the neighbouring cells.
Maybe it sounds a bit primitive but:
No n^2 algorithms
No assumption about ordering of the input
No need to additionally process markers which are not going to be shown
The code for the grid:
Note - I come from the C++ world (got here through [algorithm] tag) so I'll stick to the pseudo-C++. I do not know the API of the mapview. But I would be surprised if this couldn't be efficiently translated into whatever language/library you are using.
Input:
- list of markers
- the rectangle viewing window in world coordinates (section of world we are currently looking at)
In the simplest form, it would look something like this:
void draw(MarkerList mlist, View v) {
//binning:
list<Marker> grid[densityX][densityY]; //2D array with some configurable, fixed density
foreach(Marker m in mlist) {
if (m.within(v)) {
int2 binIdx;
binIdx.x=floor(densityX*(m.coord.x-v.x1)/(v.x2-v.x1));
binIdx.y=floor(densityY*(m.coord.y-v.y1)/(v.y2-v.y1));
grid[binIdx.x][binIdx.y].push(m); //just push the reference
}
//drawing:
for (int i=0; i<densityX; ++i)
for (int j=0; j<densityY; ++j) {
if (grid[i][j].size()>N) {
GroupMarker g;
g.add(grid[i][j]); //process the list of markers belonging to this cell
g.draw();
} else {
foreach (Marker m in grid[i][j])
m.draw()
}
}
}
The problem that might appear is that an unwanted grid split may appear within some clustered group, forming two GroupMarkers. To counter that, you may want to consider not just one grid cell, but also its neighbors in the "\drawing" section, and - if grouped - mark neighboring cells as visited.
The following pragmatic solution based on pixel distance really worked best for me:
http://www.appelsiini.net/2008/11/introduction-to-marker-clustering-with-google-maps
I converted Cygnus X1's answer to Java. Put this method in your custom Overlay and modify drawSingle() and drawGroup() to suit your needs. You improve performance too, like converting the ArrayLists to primitive arrays.
#Override
public void draw(Canvas canvas, MapView mapView, boolean shadow) {
// binning:
int densityX = 10;
int densityY = 10;
// 2D array with some configurable, fixed density
List<List<List<OverlayItem>>> grid = new ArrayList<List<List<OverlayItem>>>(
densityX);
for(int i = 0; i<densityX; i++){
ArrayList<List<OverlayItem>> column = new ArrayList<List<OverlayItem>>(densityY);
for(int j = 0; j < densityY; j++){
column.add(new ArrayList<OverlayItem>());
}
grid.add(column);
}
for (OverlayItem m : mOverlays) {
int binX;
int binY;
Projection proj = mapView.getProjection();
Point p = proj.toPixels(m.getPoint(), null);
if (isWithin(p, mapView)) {
double fractionX = ((double)p.x / (double)mapView.getWidth());
binX = (int) (Math.floor(densityX * fractionX));
double fractionY = ((double)p.y / (double)mapView.getHeight());
binY = (int) (Math
.floor(densityX * fractionY));
// Log.w("PointClusterer absolute", p.x+ ", "+p.y);
// Log.w("PointClusterer relative", fractionX+ ", "+fractionY);
// Log.w("PointClusterer portion", "Marker is in portion: " + binX
// + ", " + binY);
grid.get(binX).get(binY).add(m); // just push the reference
}
}
// drawing:
for (int i = 0; i < densityX; i++) {
for (int j = 0; j < densityY; j++) {
List<OverlayItem> markerList = grid.get(i).get(j);
if (markerList.size() > 1) {
drawGroup(canvas, mapView, markerList);
} else {
// draw single marker
drawSingle(canvas, mapView, markerList);
}
}
}
}
private void drawGroup(Canvas canvas, MapView mapView,
List<OverlayItem> markerList) {
GeoPoint point = markerList.get(0).getPoint();
Point ptScreenCoord = new Point();
mapView.getProjection().toPixels(point, ptScreenCoord);
Paint paint = new Paint();
paint.setTextAlign(Paint.Align.CENTER);
paint.setTextSize(30);
paint.setAntiAlias(true);
paint.setARGB(150, 0, 0, 0);
// show text to the right of the icon
canvas.drawText("GROUP", ptScreenCoord.x, ptScreenCoord.y + 30, paint);
}
private void drawSingle(Canvas canvas, MapView mapView,
List<OverlayItem> markerList) {
for (OverlayItem item : markerList) {
GeoPoint point = item.getPoint();
Point ptScreenCoord = new Point();
mapView.getProjection().toPixels(point, ptScreenCoord);
Paint paint = new Paint();
paint.setTextAlign(Paint.Align.CENTER);
paint.setTextSize(30);
paint.setAntiAlias(true);
paint.setARGB(150, 0, 0, 0);
// show text to the right of the icon
canvas.drawText("SINGLE", ptScreenCoord.x, ptScreenCoord.y + 30,
paint);
}
}
public static boolean isWithin(Point p, MapView mapView) {
return (p.x > 0 & p.x < mapView.getWidth() & p.y > 0 & p.y < mapView
.getHeight());
}
}
Assuming your markers are grouped together in an ItemizedOverlay you could create a method which was called when the map was zoomed. This would compare pixel co-ordinates of each marker to see if they overlap and set a flag. Then in the draw method you could draw either the grouped marker or individuals;
Something like:
//this would need to be wired to be called when the mapview is zoomed
//it sets the drawgrouped flag if co-ordinates are close together
Boolean drawGrouped=false;
public void onMapZoom(MapView mapView){
//loop thru overlay items
Integer i,l=this.size();
OverlayItem item;
Integer deltaX=null,deltaY=null;
Projection proj = mapView.getProjection();
Point p=new Point();
Integer x=null,y=null;
Integer tolerance = 10; //if co-ordinates less than this draw grouped icon
for(i=0;i<l;i++){
//get the item
item=this.getItem(i);
//convert the overlays position to pixels
proj.toPixels(item.getPoint(), p);
proj.toPixels(item.getPoint(), p);
//compare co-ordinates
if(i==0){
x=p.x;
y=p.y;
continue;
}
deltaX=Math.abs(p.x-x);
deltaY=Math.abs(p.y-y);
//if the co-ordinates are too far apart dont draw grouped
if(deltaX>tolerance || deltaY>tolerance){
drawGrouped=false;
return;
}
x=p.x;
y=p.y;
}
//all co-ords are within the tolerance
drawGrouped=true;
}
public void draw(android.graphics.Canvas canvas, MapView mapView, boolean shadow){
if(drawGrouped==true){
//draw the grouped icon *needs to be optimised to only do it once
drawGrouped(canvas,mapView,shadow);
return;
}
//not grouped do regular drawing
super.draw(canvas, mapView, shadow);
}
What you are looking for is usually called clustering. There are common techniques to do this, you can refer, for example, to this SO question, it leads to this post.
The basic idea is to divide the map on squares based on the current zoom level (you can cache calculations based on the zoom level to avoid recalculation when the user starts zooming), and to group them based which square they belong to. So you end up having some sort of grouping based on zoom level, ie for level 1-5 just draw the markers, for level 5-8 group them in squares of 20 miles, for 9-10 in squares of 50 miles, and so on.
Here is another relevant question on SO that you may want to take a look, not sure about the performance of this though: Android Maps Point Clustering
If your markers are grouped, you'll have a fair idea at what zoom level you should be displaying individual markers or the group marker e.g. zoom level > 17 then display individual markers, otherwise display the group marker. I used code something like this in my ItemizedOverlay to change my markers:
#Override
public void draw(Canvas canvas, MapView mapv, boolean shadow)
{
int zoom = mapv.getZoomLevel();
switch(zoom)
{
case 19:
setMarkersForZoomLevel19();
break;
case 18:
setMarkersForZoomLevel18();
break;
case 17:
setMarkersForZoomLevel17();
break;
case 16:
setMarkersForZoomLevel16();
break;
default:
// Hide the markers or remove the overlay from the map view.
mapv.getOverlays().clear();
}
area.drawArea(canvas, mapv);
// Putting this call here rather than at the beginning, ensures that
// the Overlay items are drawn over the top of canvas stuff e.g. route lines.
super.draw(canvas, mapv, false);
}
private void setMarkersForZoomLevel19()
{
for (JourneyOverlayItem item : mOverlays)
{
item.setMarker(areaPointIcon48);
}
}
If its possible to have the individual markers in a collection, you could easily get the largest and smallest latitude and longitude and the difference between them will give you the latitude and longitude span (this could then be used to zoom to the span to show the group of markers). Divide the spans by 2 and you should have the centre point for placing the group marker.
This is the approach that I used. However, it's O(n^2).
The pins must be sorted based on prominent.
Pick pin with the highest prominent. Look at all pins around it. Absorb pins near that pin.
Then move on to the next highest prominent pin. Do the same. Repeat.
Simple.
Things get complicated if you move the map around, zooming in, zooming out, and you want to ensure that the new pins are not being redrawn. So you check each cluster if they have to split during zoom in, and then you check each cluster if they have to merge during zoom out. Then you remove pins that's gone and add new pins. For every pin you add, you check whether they should join a cluster or form their own cluster.