Structure of Land/WaterMaskPolygons

This is a layered structure and some header information. In the BGLHeader, there are many common parts with the Vector based Textured Polygons.

ヘッダー情報も含めた階層構造です。 BGLHeader はVector based Textured Polygonsと共通部分が多いです。

BGLHeader
TDFTerrainFileHeader
LWMFileHeader
LWMIndexHeader
LWMIndexEntry
LWMCellID

LWM Data Area

LWMPoly2

LWMPoint

【LWM Data Area】

There are two types of LWM polygons : AreaFill and AreaDrawPolygons A polygon later in the stream can overwrite a prior polygon. All polygons are followed by wAttrib, iHeight and iFraction.

LWMのポリゴン形式は２種類あります : AreaFill , AreaDrawPolygons 後ろに行くほど描画上で優先される特性をもっています。 それぞれにwAttrib,iHeight,iFractionという属性があります。

wAttrib = 0(water), 1(land), 2(flatten)
iHeight = (height in meters)
iFraction=(height multiplied by 128)

The height will be iHeight + (iFraction / 128).

【LWMPoly2(AreaDrawPolygons)】
LWMPoly2 = Number of point is 1 to 62
LWMPoly2Ex = Number of point is from 63 to 317

【LWMPoint(AreaDrawPolygons)】
x=0-255, y=0-255
The northwest corner is the starting point : (0,0)

【dwAttrib/wAttribについて】
Use dwAttrib to a Cell.
Use wAttrib to an Area.

0=water, 1=Land, 2=Flatten, 3=Transparent
(1=Land以外は必ずiHeightiFractionがある)

Setting value of original LWM

flt	AreaFill/ wAttrib=2(Flatten)
	AreaDrawPolygons/ wAttrib=2(Flatten)
hyp	AreaFill/ wAttrib=0(Water)
	AreaDrawPolygons/ wAttrib=3(Transparent)