# mark own positions in tiles of a slippy map

Hi Community,

while playing with the osm i start to code an php script that loads all necessary tiles of an slippymap. Now i got a Problem to draw Locationspoints (mark own Position). I get the the Position from my Android Smartphone that uses GPS. A own Logger app writes lat and lon Data in a CSV File.

For Example:

Step 1:
I load the tile in Zoomlevel 16 of lat=50.31142830848694 and lon=7.553218603134155. I get the Tilenumber with

``````
\$xtile = floor(((\$lon + 180) / 360) * pow(2, \$zoom));
\$ytile = floor((1 - log(tan(deg2rad(\$lat)) + 1 / cos(deg2rad(\$lat))) / pi()) /2 * pow(2, \$zoom));

``````

Step 2: (Here i got my Problem)
Now a want to mark the Point of lat=50.31142830848694 and lon=7.553218603134155 in the loaded Tile of the Slippymap.
I do it like this:

``````
\$n = pow(2, \$zoom);
\$lon_deg = \$xtile / \$n * 360.0 - 180.0;
\$lat_deg = rad2deg(atan(sinh(pi() * (1 - 2 * \$ytile / \$n))));

\$lat_diff = (\$lat-\$lat_deg);
\$lon_diff = (\$lon-\$lon_deg);

// 1Pixel = 2.387 Metre in Zoomlevel 16
\$scaleToPixel = 2.387;
\$x = intval(abs(\$lat * 6378137) / \$scaleToPixel);
\$y = intval(abs(\$lon * 6378137) / \$scaleToPixel);

imagefilledellipse(\$image, \$y, \$x, 2, 2, \$color);

``````

But the drawed Points arent exactly on the Position lat=50.31142830848694 and lon=7.553218603134155.

Here you can see it:
http://www.create-your-site.de/versatz.png

I think that happens because my calculation is bad…

If anyone can help me it can save the Day 