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

Overview

This page is a living proposal for improving the scalability of the Tile Service.
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.
​OpenLayers. Layer. MapGuide
​#995 (add support for MapGuide OS layer type) - OpenLayers - Trac

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,
returning status codes of 200 ok or 404 Not Found respectively. This allows the server to
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
and management of the tile caches.

Cacheability by HTTP

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

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
to the Mapguide Server. This could done with a serverconfig.ini default and then an overriding parameter in the
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

WMS Cache headers - see above.

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.

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

TMS

TMS