[[PageOutline]]

This page is part of the [wiki:Future MapGuide Future] section, where ideas are proposed and refined 
before being turned into RFCs (or discarded).  Visit the [wiki:Future] page to view more!

= Overview =

This page is a living proposal for improving the scalability of the Tile Service. [[BR]]
Mapguide supports tiled maps via both WMS and it's own Tile Service using GETTILETIMAGE.

Recently support was added in Openlayers & Fusion to access the Tile Service via an API.[[BR]]
[http://dev.openlayers.org/apidocs/files/OpenLayers/Layer/MapGuide-js.html OpenLayers. Layer. MapGuide][[BR]]
[http://trac.openlayers.org/ticket/995 #995 (add support for MapGuide OS layer type) - OpenLayers - Trac][[BR]]


= API Ideas =

'''SETTILEIMAGE''' would allow the tile cache to seeded without needing to have remote access to the server file system.

'''GETTILEPARAMS''' would return a list of scale ranges, tile sizes and bounds for a given tile cache.

'''GETTILECACHE''' would return a 'map' of the tile cache, listing which tiles exist and which ones haven't yet been created

'''HAVETILEIMAGE''' would enable a server to poll another server(s) in the cluster, [[BR]]
returning status codes of 200 ok or 404 Not Found respectively. This allows the server to[[BR]]
check the tile cache without triggering a tile render on the polled server.

These would enable more extensive API based management of a cluster of Mapguide servers, via accurate seeding[[BR]]
and management of the tile caches. 

= Cacheability by HTTP =

[wiki:MapGuideRfc11] added support for a '''Stateless Http GETTILEIMAGE request''', however, these tiles are served [[BR]]
without any cache headers which means they can only be proxied using a custom 'aggressive' proxy service. [[BR]]

[ticket:467 Add proper cache headers & file date to GETTILEIMAGE response]. 

One of the the issues to be resolved is how long to set the cache headers to cache the tiles before checking back [[BR]]
to the Mapguide Server. This could done with a serverconfig.ini default and then an overriding parameter in the [[BR]]
ResourceHeader. 

== API additions to MgTileService ==

To support HTTP cacheability we need to be able to do the following via the MgTileService:

 a) Get timestamp information about a generated tile (to be able to apply expiry dates)

 b) "Peek" at the timestamp for a tile that may or may not be generated (to be able to compare against dates from if-modified-since headers)

An API addition to MgTileService like the one below should be able to support the above scenarios.

{{{

class MG_MAPGUIDE_API MgTileService : MgService
{
PUBLISHED_API:
   /// Returns the timestamp of when the tile for the specified map/group/row/col was generated. Returns NULL if no such tile exists
   ///
   MgDateTime* GetTileCreationDate(MgMap* map, CREFSTRING baseMapLayerGroupName, INT32 tileColumn, INT32 tileRow);

   /// Returns the timestamp of when the tile for the specified map/group/row/col/scale was generated. Returns NULL if no such tile exists
   ///
   MgDateTime* GetTileCreationDate(MgResourceIdentifier* mapDefinition, CREFSTRING baseMapLayerGroupName, INT32 tileColumn, INT32 tileRow, INT32 scaleIndex);

   /// Returns the specified base map tile for the given map.  If a cached tile
   /// image exists it will return it, otherwise the tile is rendered and added
   /// to the cache.
   MgTile* GetTile(MgMap* map, CREFSTRING baseMapLayerGroupName, INT32 tileColumn, INT32 tileRow);

   /// Returns the specified base map tile for the given map.  If a cached tile
   /// image exists it will return it, otherwise the tile is rendered and added
   /// to the cache.
   ///
   MgTile* GetTile(MgResourceIdentifier* mapDefinition, CREFSTRING baseMapLayerGroupName, INT32 tileColumn, INT32 tileRow, INT32 scaleIndex);
};
}}}

MgTile is defined like so.

{{{
class MG_MAPGUIDE_API MgTile : public MgSerializable
{
PUBLISHED_API:
    /// Returns the tile image
    ///
    MgByteReader* GetImage();

    /// Returns the date this tile was created
    ///
    MgDateTime* GetCreationDate();
};

}}}

== MapAgent modifications ==

TBD

= WMS =

[ticket:286 WMS Cache headers] - see above.

[ticket:285 Publish MapDefinitions via WMS] Currently only layers are exposed via WMS, maps could be as well.  

The WMS service doesn't currently use the tile cache, which means every WMS request is rendered. [[BR]]

Linking the WMS service up to utilize the tile cache would dramatically improve the performance [[BR]]
and capacity of WMS with Mapguide.[[BR]]

= TMS = 

[wiki:GoogleSoC2007#TileMapServicePublishing TMS]