[mapserver-users] Order of layers

[Marek Bąk]

Dear All,

I'm working on project  for which maps in different scales are delivered 
by customer. Higher scale means more details but less coverage. Output 
can have glitches but it cannot have any gaps (it should works in 
similar way like in opencpn - high detailed maps shadow less detailed 
but at the same moment you can enable and disable groups of layers). So 
having layers like that:

LAYER (GROUP "WATER", NAME "WATERBIG", COMPOP src-over)

LAYER (GROUP "LAND", NAME "LANDBIG", COMPOP src-over)

LAYER (GROUP "TREES", NAME "TREESBIG", COMPOP src-over)

LAYER (GROUP "WATER", NAME "WATERMID", COMPOP src-over)

LAYER (GROUP "LAND", NAME "LANDMID", COMPOP src-over)

LAYER (GROUP "TREES", NAME "TREESMID", COMPOP src-over)

LAYER (GROUP "WATER", NAME "WATERSMALL", COMPOP src-over)

LAYER (GROUP "LAND", NAME "LANDSMALL", COMPOP src-over)

LAYER (GROUP "TREES", NAME "TREESSMALL", COMPOP src-over)

I'd have output in which:

MID replaces BIG within its EXTENT (completely both transparent and 
non-transparent pixels)

SMALL replaces BIG and MID within its EXTENT (completely both 
transparent and non-transparent pixels)

But I'm having problem to force reset some EXTENT to transparent color. 
Someting like:

LAYER (GROUP "WATER", NAME "WATERBIG", COMPOP src-over)

LAYER (GROUP "LAND", NAME "LANDBIG", COMPOP src-over)

LAYER (GROUP "TREES", NAME "TREESBIG", COMPOP src-over)

LAYER (GROUP "RESET", NAME "RESETMID", COMPOP ??? - what to put here to 
have precalcuated EXTENT (not whole buffer) of render buffer to reset to 
transparent

LAYER (GROUP "WATER", NAME "WATERMID", COMPOP src-over)

LAYER (GROUP "LAND", NAME "LANDMID", COMPOP src-over)

LAYER (GROUP "TREES", NAME "TREESMID", COMPOP src-over)

Is it possible to achieve with MapServer using GROUP attribute and some 
kind reset extent layer?


Regards,

Marek