\subsubsection{DEM}
-This is a library of routines distributed as part of Flight Gear.
-This library has routines to parse the 3 arcsec DEM file format,
-approximate the regular grid of height data, with an irregular grid,
-and interpolate the elevation of any arbitrary point inside the grid.
+This library has routines to parse the 3 arcsec DEM file format, and
+output a square section corresponding to a specified tile.
-An irregular grid can often represent the same level detail as a
-regular grid with 4-6x fewer polygons. This is very desirable in a
-flight sim where both detail and rendering speed is very important.
+\subsubsection{Polygon}
-Another feature of an irregular grid is that it carries fewer
-artifacts that could provide negative training value to pilots. For
-instance a regular grid could give a pilot non-realistic cues for
-determining north/south/east/west.
+This lib contains routines to assign a unique id number to each
+polygon before it is clipped against tial boundaries. We can use this
+unique id later on to match up the edges of polygons across tile
+boundaries.
+This lib also contains routines to track and assign names (types) to
+each polygon so we can color it with the correct texture at run time.
\subsubsection{Triangle}
\subsection{Preprocessing tools}
The preprocessing tools are responsible for inputing raw world data,
-clipping it to the appropriate scenery tiles, outputing it into the
-workspace directory tree.
+clipping it to the appropriate scenery tiles, and outputing it into
+the workspace directory tree.
The scenery assembly and creation tools work on each tile
individually, so they expect all the relevant information for a tile
to already be there.
+\subsubsection{DemChop}
+
+This utility inputs 3 arcsec dem files, chops the data up along tile
+boundaries and outputs the result into the scenery workspace.
+
+\subsubsection{DemInfo}
+
+Reads the ``A'' record from a 3 arcsec DEM file and dumps some
+pertinent information.
+
+\subsubsection{DemRaw2ascii}
+
+This tool will input the 30 arcsec raw DEM format, split it up into 1
+x 1 degree sections, and output the result into the 3 arcsec format so
+it can be fed through the scenery pipeline. (Note to self, at some
+point, this could be updated to work like DemChop and output the tile
+chunks directly.)
+
\subsubsection{GenAirports}
This tools inputs an ascii specification of the airports of the world
that looks like the following:
\begin{verbatim}
-KORD Chicago O Hare International
- -087.917774 41.976778 13000 200 140 155154 14 R 668
- -087.902380 41.969040 10141 150 90 154154 09 R 668
- -087.903546 41.991918 10003 150 140 155154 14 L 668
- -087.889594 41.961618 8071 150 41 154154 04 R 668
- -087.903705 41.983954 7967 150 90 154154 09 L 668
- -087.905138 41.989606 7500 150 39 142144 04 L 668
- -087.900410 41.990086 5341 150 180 131131 18 x 668
+A KORD 41.979595 -087.904464 668 CYY Chicago O Hare International
+R 04L 41.989606 -087.905138 039.39 7500 150 AHYN NNNLYN NNNNNY
+R 04R 41.961618 -087.889594 041.40 8071 150 AHYN YNNNNY YNNNNY
+R 09L 41.983954 -087.903705 089.70 7967 150 AHYN YNNNNY YNNNNY
+R 09R 41.969040 -087.902380 089.88 10141 150 AHYN YNNNNY YNNNNY
+R 14L 41.991918 -087.903546 140.10 10003 150 AHYN YNNBYN YNNNNY
+R 14R 41.976778 -087.917774 140.08 13000 200 AHYN YNNBYN YNNNNY
+R 18 41.990086 -087.900410 180.00 5341 150 AMNN NNNNNN NNNNNN
\end{verbatim}
For each airport, a bounding polygon is generated, and written as a
center point, but the airport will need to be clipped out of the base
terrain from any tiles it might spill over into.
+Robin Peel (robin@cpwd.com) maintains this data base, primarily for
+use with X-Plane, but lets us use it too. His distribution contians a
+much more detailed description of the fields and formats.
+
\subsubsection{ShapeFile}
The ShapeFile tool will take the polygons from shapefiles (via GFC),
this. Each polygon that is written out (no matter what the source or
type) should have a unique id number assigned to it.
-\subsubsection{DemRaw2ascii}
-
-This tool will input the 30 arcsec raw DEM format, split it up into 1
-x 1 degree sections, and output the result into the 3 arcsec format so
-it can be fed through the scenery pipeline.
-
-\subsubsection{Dem2node}
-
-This tool takes the raw DEM files and calls routines from libDEM.a to
-create the irregular grid approximation of the original data. The
-elevation data is writen to the to the appropriate tile in the scenery
-work space.
-
\subsection{Scenery generation tools}
Issues:
-Combining height data, polygon data.
+\begin{itemize}
+\item Combining height data, polygon data.
-Triangulating / tri-stripping / tri-fanning.
+\item Triangulating / tri-stripping / tri-fanning.
-Matching vertices and normals along edges and at corners.
+\item Matching vertices and normals along edges and at corners.
-Resolving conflicts in data:
+\item Resolving conflicts in data:
overlapping polygon areas.
conflicting height data between airports and DEM data
+\end{itemize}
Here's the basic process to create scenery:
to the FGFS scenery format and copy them from the work space directory
tree into the final scenery directory tree.
+\subsubsection{Array}
+
+This library reads in the regular grid data written by the DemChop
+preprocessing tool. It has a fit routine which approximates the
+regular grid of height data with an irregular grid, and interpolate
+the elevation of any arbitrary point inside this grid.
+
+An irregular grid can often represent the same level detail as a
+regular grid with 4-6x fewer polygons. This is very desirable in a
+flight sim where both detail and rendering speed is very important.
+
+Another feature of an irregular grid is that it carries fewer
+artifacts that could provide negative training value to pilots. For
+instance a regular grid could give a pilot non-realistic cues for
+determining north/south/east/west.
+
+\subsubsection{Clipper}
+
+This library makes heavy use of ``the generic polygon clipper''. The
+polygons of each tile are clipped against the tile boundaries as well
+as any higher priority polygons for that tile. To do this the library
+processes the polygons from highest priority to lowest and
+incrimentally builds up an accumulation ``super-polygon''. This
+super-polygon is the union of all the polygons processed so far. As
+each polygon is processed, it is first clipped against this
+super-accumlation-polygon. What's left after the clip is the new
+shape of the polygon. This is the scheme for eliminating overlapping
+features on a priority basis. In the end we can create a base-terrain
+polygon out the remaining open areas of the tile that weren't covered
+by any other polygons. This way we end up with a set of ``puzzle''
+pieces that together form the complete tile with no overlaps and no
+gaps.
+
+
+% \subsubsection{Dem2node}
+%
+% This tool takes the raw DEM files and calls routines from libDEM.a to
+% create the irregular grid approximation of the original data. The
+% elevation data is writen to the to the appropriate tile in the scenery
+% work space.
+
% \subsubsection{Areas}
% \subsubsection{AssemTris}
-% \subsubsection{Clipper}
% \subsubsection{FixNode}
% \subsubsection{FixObj}
% \subsubsection{SplitTris}
\subsection{Miscellaneous Utilities}
-\subsubsection{DemInfo}
-
-Reads the ``A'' record from a 3 arcsec DEM file and dumps some
-pertinent information.
-
\subsubsection{tile-sizes.pl}
Generates the width of a 1/8 x 1/8 degree tile at various latitudes.
%------------------------------------------------------------------------
% $Log$
+% Revision 1.3 1999/03/13 21:42:37 curt
+% Updated to match current scenery generation tools progress.
+%
% Revision 1.2 1999/03/08 21:59:52 curt
% Updated based on current efforts.
%
projects / flightgear.git / commitdiff