Using .map file as a raster layer source

[szekerest]

It would be useful to make the possibility to use a .map file as a data source 
of a raster layer in another .map file. I've attached a modified mapraster.c 
that ensures this feature.

The main benefits of this enhancement are:

1. High number of maps could be joined into a single map. The maps could be 
organized hierarchically.
2. Tileindex support can be used to filter the maps to be drawn.
3. With the code attached there's no need to create temporary images in the 
filesystem as with WMS layers

Any comments would be appreciated,

Tamas Szekeres

[szekerest]

modified mapraster.c for achieving this functionality

[fwarmerdam]

Tamas, 

This is an interesting addition, but I am a bit uncertain whether it is a 
good general addition to MapServer.  Once concern I have is about the fact
that sub-maps can generally not be influenced by the calling map except for
setting of the target extent. Are we likely to find people wanting more control
than this, and needing to build mechanisms to satisfy it?  Does this capability
really give us something we wouldn't otherwise have? 

A few details:
 o The patch does not address RGB, RGBA or other types of render results.  It
   seems that it assumes the result of the drawMap() is an 8bit GD image result.
   At the very least it ought to error out gracefully for other return results.

 o We would really need appropriate user documentation in order to incorporate
   this as a supported feature. 

Contrats on a cool hack!  (I mean hack in the most positive sense).