Hi everyone,

I have a problem that I can't solve and I was wondering if anyone
might be able to help.  I am trying to write a php script that will
take a lat/lng point and calculate the bbox for the enclosing tile and
the pixel coordinates to that lat/lng from the upper left corner of
the tile.  I already know how to do this in javascript using the
google map api (i'll paste the javascript below, but I can't figure
out how to do it in php without the api.  I want to do this because I
am using a WMS getFeatureInfo query to query my map, but I would like
to be able to run those queries outside of the map api on the server
side.

I've searched all over the web, and I just can't find something that
helps me figure this problem out. Is there any way you might be able
to lead me in the right direction?  This for a non-profit site that
maps roadless areas in US forest service land.  You can see it here:
http://roadlessland.org (some of you have already seen this)

thanks so much,
nelson

Here is the javascript that I am currently using:

        var z;  // zoom level at which to calculate the tile

        var proj = map.getCurrentMapType().getProjection();
        var pt = proj.fromLatLngToPixel(latlng,z);

        var tile_coord_x = Math.floor(pt.x/256);
        var tile_coord_y = Math.floor(pt.y/256);
        var a = new GPoint(tile_coord_x,tile_coord_y);
        var lULP = new GPoint(a.x*256,(a.y+1)*256);
        var lLRP = new GPoint((a.x+1)*256,a.y*256);

        var lUL =
G_NORMAL_MAP.getProjection().fromPixelToLatLng(lULP,z,false);
        var lLR =
G_NORMAL_MAP.getProjection().fromPixelToLatLng(lLRP,z,false);

        var lBbox=lUL.x+","+lUL.y+","+lLR.x+","+lLR.y;

//      The bbox coordinates:
        var bbox = lBbox;

//      Get the pixel coordinates of the lat/lng point

        var local_x = pt.x % 256;
        var local_y = pt.y % 256;

        var coords = 'x='+local_x+'&y='+local_y;

Read also here : http://cfis.savagexi.com/articles/2006/05/03/google-maps-deconstructed
The big magic it is in the projection formulas, Google uses a
different Mercator projection for each zoom level, after you will
define projection formulas you will can easily convert long/lat to
pixels(measure unit in projection used) for a given zoom level and
then to calculate the enclosing tile and of course top and left pixel
from 0,0 of tile.

On Jan 17, 9:58 pm, nelsong <nelson.g...@gmail.com> wrote:

On Jan 18, 8:51 am, vasile cotovanu <vasile.cotov...@gmail.com> wrote:

huh ????

The only difference is the shift amount (zoom parameter).

    http://www.polyarc.us/buildurl.js

Look at the LToX & LToY functions. Ignore the "w" parameter which is
the UTM zone.  I stripped out the UTM projection stuff used by
TerraServer.

Thanks all,

The article on deconstructing google maps was interesting, but still a
bit far from what I needed to accomplish.  I found the coordtotile.php
function separately, and I realized that it had what I needed (
http://mapki.com/coordtotile.2.phps - also found here:
http://mapki.com/wiki/Lat/Lon_To_Tile )

After some work I figured out how to get the info I needed out of it
by adding a short function.  For anyone interested, I will paste it
below.  This is a function that will spit out a wms query string (bbox
and xy coordinates) given a lat/lng pair and a google zoom.  Just add
this to the end of coordtotile.2.php - then use the function
get_query_string($lat,$lng,$z).  The only caveat is that coordtotile.
2.php does not seem to work well with zooms less than 8 (I imagine it
has something to do with crossing the zero longintude line, but I
didn't investigate further.)

Also, for anyone interested, coordtotile.2.php must have been
developed before google map switched their zoom around, because I had
to add -25 to the zoom so that the results match with current google
map zooms.

best,
nelson

<?
function get_query_string($lat,$lng,$z) {
$z = 25 - $z;
$tile = new Tile($lat,$lng,$z);

$tilelng = $tile->getTileLatLong();
$tilelng = $tilelng->x;
$tilelat = $tile->getTileLatLong();
$tilelat = $tilelat->y;

$tilelat2 = $tilelat;
$tilelng2 = $tilelng;
$lat2 = $lat;
$lng2 = $lng;

while($tilelat2 == $tilelat) {
$lat2 = $lat2 - .001;
$tile = new Tile($lat2,$lng2,$z);
$tilelat2 = $tile->getTileLatLong();
$tilelat2 = $tilelat2->y;

while($tilelng2 == $tilelng) {
$lng2 = $lng2 + .001;
$tile = new Tile($lat2,$lng2,$z);
$tilelng2 = $tile->getTileLatLong();
$tilelng2 = $tilelng2->x;

$thgt = $tilelat - $tilelat2;
$twdt = $tilelng2 - $tilelng;
$xpt = round(($lng-$tilelng)*256/$twdt);
$ypt = round(($tilelat-$lat)*256/$thgt);

$bbox =  $tilelng.','.$tilelat2.','.$tilelng2.','.$tilelat;
$pt_coords =  '&x='.$xpt.'&y='.$ypt;
$query = 'bbox='.$bbox.$pt_coords;
return $query;

?>

On Jan 18, 8:40 am, bratliff <bratl...@umich.edu> wrote: