Map Tile Layers and Map Tile Sources Storage of Map Image Tiles Coordinate System for Map Tiles

Oracle Maps 8-9 As shown in Figure 8–4 , when the map tile server receives a request for a map tile, it searches for the tile in the cache storage system. If the tile is cached, the map tile server sends the tile to the client. If the tile is not cached, the map tile server fetches the tile, saves in the cache, and sends it to the client. You can use the MapViewer administration tool to manage the map tile server.

8.2.1 Map Tile Server Concepts

This section explains map tile server concepts that you need to know to be able to use Oracle Maps effectively.

8.2.1.1 Map Tile Layers and Map Tile Sources

All map tile layers are managed by the map tile server. The map tile server fetches and stores the map image tiles that belong to the map tile layer and returns map image tiles to the client. The map tile server can manage multiple map tile layers. Each map tile layer can have multiple predefined zoom levels. Each zoom level is assigned a zoom level number ranging from 0 to n-1, where n is the total number of zoom levels. Zoom level 0 is the most zoomed out level and zoom level n-1 is the most zoomed in level. The map is evenly divided into same-sized small map image tiles on each zoom level. Clients specify a map tile by its zoom level and tile mesh code. A map tile layer can come from two different types of sources: ■ Internal MapViewer base maps rendered by the MapViewer map rendering engine. A MapViewer base map consists of a set of predefined themes and must be predefined in the database view USER_SDO_MAPS. ■ Maps rendered by an external Web map services providers. An external Web map services provider is a server that renders and serves maps upon client requests over the web. If you properly configure an adapter that can fetch maps from the external map services provider, the map tile server can fetch and cache map tiles generated by the external map services provider. A MapViewer instance other than the MapViewer inside which the map tile server is running is also considered an external map services provider.

8.2.1.2 Storage of Map Image Tiles

Oracle Maps uses the local file system to store cached image tiles. You can customize the path that is used for this storage as part of the map tile server configuration settings.

8.2.1.3 Coordinate System for Map Tiles

Map images are cached and managed by the map tile server as small same-size rectangular image tiles. Currently we support tiling on any two-dimensional Cartesian coordinate system. A geodetic coordinate system can also be supported when it is mapped as if it is a Cartesian coordinate system, where longitude and latitude are treated simply as two perpendicular axes, as shown in Figure 8–5 . 8-10 Oracle Fusion Middleware Users Guide for Oracle MapViewer Figure 8–5 Tiling with a LongitudeLatitude Coordinate System On each zoom level, the map tiles are created by equally dividing the whole map coordinate system along the two dimensions X and Y, which in Figure 8–5 represent latitude and longitude. The map tile server needs this dimensional information of the map coordinate system in order to create map image tiles, and therefore you must include this information in the map tile layer configuration settings. The whole map coordinate system can be represented by a rectangle, and its boundary is specified by Xmin, Ymin and Xmax, Ymax, where Xmin is the minimum X value allowed in the coordinate system, Ymin is the minimum Y value allowed, Xmax is the maximum X value allowed and Ymax is the maximum Y value allowed. In Figure 8–5 , Xmin is –180, Ymin is –90, Xmax is 180, and Ymax is 90. You must also specify the spatial referencing ID SRID of the coordinate system to enable the map tile server to calculate map scales.

8.2.1.4 Tile Mesh Codes