3D coverages in WMS

[Dimitar Misev]

WMS doesn't seem to support 3D coverages? It would be useful to allow them in some way, perhaps by a mandatory rasql style. E.g. consider this example:

Change detection by putting NDVI indexes of different dates in each band of the output; tyrol_6 is a landsat cube with 6 time slices:

	for c in (tyrol_6) return encode(
	{
		red:   (((c.nir - c.red) / (c.nir + c.red))[ansi("2015-08-20")] * 255);
		green: (((c.nir - c.red) / (c.nir + c.red))[ansi("2015-07-19")] * 255);
		blue:  (((c.nir - c.red) / (c.nir + c.red))[ansi("2015-06-17")] * 255)
	}, 
	"png")

rasql fragment:

    { (($Iterator[*:*,*:*,5].3 - $Iterator[*:*,*:*,5].2) / ($Iterator[*:*,*:*,5].3 - -$Iterator[*:*,*:*,5].2)) * 255, (($Iterator[*:*,*:*,3].3 - $Iterator[*:*,*:*,3].2) / ($Iterator[*:*,*:*,3].3 - -$Iterator[*:*,*:*,3].2)) * 255, (($Iterator[*:*,*:*,1].3 - $Iterator[*:*,*:*,1].2) / ($Iterator[*:*,*:*,1].3 - -$Iterator[*:*,*:*,1].2)) * 255 }