Google Maps HeatMap now correctly reprojected

I posted some weeks ago my first experiment on HeatMaps over Google Maps for Flash. It was well received by the community of google maps developers and several asked for the code. I did not published it ten because there were still some things I did not understand and somehow were just magic and I had to tweak. The biggest problem was that the heatmap actually was not correctly overlaying in the map, it was clearly a Projection problem. I was plotting the coordinates in an image without reprojecting them to the Mercator projection used by google Maps.

Ok, now I have solved this by using the GoogleMapUtility.php class in the server after getting the latitudes and longitudes of my points from the database.

The final result can be viewed here (source view enabled)

Launch demo Heat Map

This is how the map would look like without reprojection:

And this is how it looks projected:

If you are overlaying a little heatmap over a small area, a city for example, you dont have to worry about reprojecting as there is not much difference. But like in this case, there is no other way.

The projection takes place on the server on this method:

public function getMercatorCoords() {
    $conn = pg_connect($this->conn_string);
    $query = "select latitude,longitude from my_table";
    $result = pg_query($conn, $query);

    $dataX = array();
    $dataY = array();

    while ($row = pg_fetch_row($result)) {
        $lat = $row[0];
        $lng = $row[1];
        $po = GoogleMapUtility::toZoomedPixelCoords($lat,$lng,0);
    
        $dataY[] = $po->y;
        $dataX[] = $po->x;
    }
    $res = array();
    $res["dataX"] = $dataX;
    $res["dataY"] = $dataY;
    return $res;
}

The GoogleMapUtility.php class can be found here. I am not sure who developed it but is widely available all over the web.

In this class I set the Tile Size to be 360, but it could had been more or less anything as long as in the Flex side then you use the same size for creating the Sprite (check the flex source code for more details).

What I would really like is to be able to do this reprojection on Flex as normally I just transfer coordinates to the client and then represent it in different ways, heatmap, grids, markers, etc.

I will try to port the GoogleMapUtility class soon to AS3 and publish it here.

I am using this code already in the widget I am developing for GBIF. It is only a small area and I dont have much data, but I am happy with it.