[ka-Map-dev] purpose of tile.php

[Tim Schaub]

I'm interested to get some feedback on this.  I can imagine three broad categories of use cases that determine how tile.php should be used.  I'm making changes to my ka-Map to handle these three cases.  I'd be happy to contribute if people agreed that it would be of general use.  If anybody can see another case that is not treated here, or if there is a problem with the way I've suggested handling these, please let me know.
 
Use cases:
 
1) Static Data/Infrequent Updates - file or database data that is updated infrequently
 
Here tile.php is used only in pre-rendering the cache.  Client side scripts could be modified so that pre-rendered tiles are accessed directly (if cache is web-accessible) - bypassing tile.php.  Whenever mapfile or data changes, cache is flushed and regenerated.
 
 
2) Static Data/Frequent Updates - file or database data that is updated frequently
 
Here tile.php is called all the time.  A version number could be used to determine when tiles should be re-rendered.
 
 
3) Dynamic Data - data derived from queries generated by the client
 
When the client generates a query (SELECT fields FROM table WHERE date > somedate - for example) tile.php could be used to do mapfile variable substitution.  In this way, if someone wants to customize their client interface to have some forms that generate queries, they don't have to customize the ka-Map core.  This can all be handled by placing %variables% in the mapfile and sending those variables to tile.php.
 
 
The client side scripts could be modified to determine when to use tile.php based on layer metadata.  A tag like "TILE_SOURCE" for example could have three possible values:
 
1) <CACHE_URL> - path to web accessible cache.  This corresponds to use case #1.  Image is requested  by client directly, without going through tile.php.
 
2) "AUTO" - default value.  Tile.php decides whether or not to render a tile.  This is how things currently work.  This would correspond with use case #2 if a version number were appended to the query to determine when to update an existing tile (bug 1041).
 
3) "FORCE_REDRAW" - always render new tile.  With variable substitution added to tile.php, this would handle use case #3.  Suggested patches in bug 1290 and 1303.
 
 
Thanks for any feedback,
Tim
 

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