http://www.vsoftonline.com/blog/?page_id=58

[ Header ]
Field			Size		Comment
-----			----		-------
magic			4			"GRGN" (0x47 0x52 0x47 0x4E)
varMaj			1			1 (v1.6 v1.7)
verMin			1			7
{ v1.7
	Field			Size		Comment
	-----			----		-------
	width			4			x size of the map (int)
	height			4			y size of the map (int)
	zoom			4			zoom, default 10.0f (float)
	numTexture		4			number of textures (int)
	maxTexName		4			maximum size of the texture names (int)
	{ * numTexture
		[ Texture ] sizeof=maxTexName
		Field		Size			Comment
		-----		----			-------
		name		maxTexName		texture name (nul terminated string)
	}
	numLightmap		4			number of lightmaps
	lmapWidth		4			??? lightmap x grid size (must be 8) (int)
	lmapHeight		4			??? lightmap y grid size (must be 8) (int)
	lmapPf			4			??? lightmap 'cells per grid'? (must be 1) (int)
	{ v1.7
		{ * numLightmap
			[ CLMInfo ] sizeof=0x100
			Field			Size		Comment
			-----			----		-------
			brightness		1*lmapWidth*lmapHeight		unsigned brightness values of the grid (must be 8x8) (uchar[8][8])
			color			3*lmapWidth*lmapHeight		RGB/BGR(?) colors of the grid (must be 8x8) (uchar[3][8][8])
		}
	}
	{ v1.6
		{ * numLightmap
			[ LMIndex ] sizeof=0x10
			Field		Size		Comment
			-----		----		-------
			a			4			(ulong)
			r			4			(ulong)
			g			4			(ulong)
			b			4			(ulong)
		}
		colorchannel		4		??? number of color channels? (int)
		{ * colorchannel
			[ ColorChannel ] sizeof=0x28
			Field		Size		Comment
			-----		----		-------
			buffer		40			(uchar[40])
		}
	}
	numSurface		4		number of surfaces
	{ * numSurface
		[ GndSurfaceFmt ] sizeof=0x28
		Field			Size		Comment
		-----			----		-------
		u[0]			4			south west u texture coordinate (float)
		u[1]			4			south east u texture coordinate (float)
		u[2]			4			north west u texture coordinate (float)
		u[3]			4			north east u texture coordinate (float)
		v[0]			4			south west v texture coordinate (float)
		v[1]			4			south east v texture coordinate (float)
		v[2]			4			north west v texture coordinate (float)
		v[3]			4			north east v texture coordinate (float)
		textureId		2			texture index (-1 for noone) (short)
		lightmapId		2			lightmap index (-1 for noone) (ushort)
		color			4			color (COLOR bgra)
	}
	{ * width*height
		{ v1.7
			[ GndCellFmt17 ] sizeof=0x1C
			Field				Size		Comment
			-----				----		-------
			height[0]			4			southWestDepth (float)
			height[1]			4			southEastDepth (float)
			height[2]			4			northWestDepth (float)
			height[3]			4			northEastDepth (float)
			topSurfaceId		4			top surface index (-1 for noone) (int)
			frontSurfaceId		4			front surface index (-1 for noone) (int)
			rightSurfaceId		4			right surface index (-1 for noone) (int)
		}
		{ v1.6
			[ GndCellFmt16 ] sizeof=0x16
			Field				Size		Comment
			-----				----		-------
			height[0]			4			southWestDepth (float)
			height[1]			4			southEastDepth (float)
			height[2]			4			northWestDepth (float)
			height[3]			4			northEastDepth (float)
			topSurfaceId		4			top surface index (-1 for noone) (short)
			frontSurfaceId		4			front surface index (-1 for noone) (short)
			rightSurfaceId		4			right surface index (-1 for noone) (short)
		}
	}
}



------------------------------------
-- alpha ---------------------------
------------------------------------
[ Header ]

Field			Size		Comment
-----			----		-------
numTexture		4			number of textures
width			4			x size of the map
height			4			y size of the map
{ *numTexture
	[ Texture ] sizeof=80
	Field		Size		Comment
	-----		----		-------
	name		80			texture name
}
{ * width*height
	[ Cell ] sizeof=0x84
	Field				Size		Comment
	-----				----		-------
	texture_up			4			texture index (-1 for noone) (int)
	texture_front		4			texture index (-1 for noone) (int)
	texture_left		4			texture index (-1 for noone) (int)
	height[0]			4			southWestDepth (float)
	height[1]			4			southEastDepth (float)
	height[2]			4			northWestDepth (float)
	height[3]			4			northEastDepth (float)
	color				4			color
	u[0]				4			south west u texture coordinate (float)
	u[1]				4			south east u texture coordinate (float)
	u[2]				4			north west u texture coordinate (float)
	u[3]				4			north east u texture coordinate (float)
	v[0]				4			south west v texture coordinate (float)
	v[1]				4			south east v texture coordinate (float)
	v[2]				4			north west v texture coordinate (float)
	v[3]				4			north east v texture coordinate (float)
	???					68			???
}