Using Geowebcache tiles stored in s3 from Google Maps for Flash

Last week I was in a code sprint for my next project on a very nice cottage. During the sprint I set up a Geoserver instance with Geowebcache to generate tiles from the World Database on Protected Areas. The tiles will be stored in S3 and distributed with CloudFront as the main goal is speed worldwide. The tiles will be used in a set of Maps in Flash around the project.

The biggest issue came when trying to generate a class to load the tiles from the default folder structure created by Geowebcache. I know I could have created my own tile folder structure generator for Geowebcache by creating my own BlobStore and modifying the FilePathGenerator to fir my needs, buuut i am not a Java lover and thought that it might be some good reasons why the good people at Geowebcache had use the current one.

The problem is that the structure is not very obvious, and I can imagine that it is because you dont want to have too many files within one single folder or you will start hitting the file system limits.

In order to use Google Maps for Flash you need to convert a request based on Zoom, X and Y tile coordinates, into a URL from where to get the tiles

If you use Geowebcache for accessing your tiles this is not a problem, use their gmap service and it will deliver your tile from wherever is in the file system. The issue is that I uploaded my whole geowebcache into S3 so I needed from the Flash client to know where to look for a x,y,z tile. With the help of Craig Mills we ported the code on Geowebcache to AS3.

The trickiest part was figuring out that Geowebcache starts its tiles from bottom left, while Google starts from top left. Dont know why they made this decission, but it is a bit of a pain. So tile z:1,x:0,y:0 in google is z:1,x:0,y:1 in geowebcache.

I thought it might be useful for someone that has similar needs so I have uploaded my classes here in case someone needs them.

Just a bit more information. I use the following command to trigger the tiling process:

curl -u geowebcache:secured -d “threadCount=01&type=reseed&gridSetId=EPSG:900913&format=image/png&zoomStart=00&zoomStop=08&minX=&minY=&maxX=&maxY=” http://localhost:8080/geowebcache/rest/seed/ppe:ppeblue

Remove the empty tiles generated (by looking if they are smaller than 663bytes)

find . -size -663c -type f -exec rm -f ‘{}’ \;

Remove the empty folders

find . -empty -type d -exec rm -rf ‘{}’ \;

And finally upload (well, sync) to S3

s3cmd sync —guess-mime-type —delete-removed —force —no-progress —acl-public /var/tiles/gwc/ppe_ppeblue/ s3://mybuket/ppe_ppeblue/