164 lines
5.7 KiB
Text
164 lines
5.7 KiB
Text
TerraGear Scenery Tools README
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==============================
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TerraGear is a collection of tools for building scenery for the
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FlightGear project. Generally, the process is done in two steps:
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1. Preprocess the original raw data. This chops up the data into
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the FG tiling scheme and saves it in a simple, intermediate
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format.
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2. Collect all the different pieces of intermediate data and
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assemble them into a 3d model of the terrain.
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There is currently no graphical front end for these tools so you will
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need to run them from the command line. Be prepaired, when building
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scenery on a world wide scale, be prepaired to burn through multiple
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gigabytes of disk space and days or weeks of crunching. Building
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smaller chunks is much more doable though.
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Building the Tools
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==================
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These tools are primarily compiled and tested under Unix with the gnu
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compilers. I believe they also build and run on windows with Cygwin.
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If anyone has patches for supporting other platforms, I will be happy
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to incorporate them.
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The process for building these tools is very similar to building the
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main FG source code.
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1. If you are using the CVS version of the source, run the
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"autogen.sh" script. If you downloaded the source tarball, then
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don't.
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2. Run the "configure" script, with optional arguments for setting
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the install prefix, etc..
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3. Run "make"
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4. Run "make install"
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Preprocessing Terrain
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=====================
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TerraGear supports several terrain data sources:
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1. 30-arcsec SRTM based terrain data covering the world (recommended
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over other 30-arcsec data sources):
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ftp://edcsgs9.cr.usgs.gov/pub/data/srtm/SRTM30/
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I don't recall the details at the moment for processing this data.
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Probably similar to the processing of the GLOBE data.
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2. 30-arcsec world wide data: GLOBE project:
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http://www.ngdc.noaa.gov/seg/topo/globe.shtml
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a) First convert the "bin" DEM format to "ascii" DEM format using
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"Prep/DemRaw2ascii/raw2ascii"
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b) Then process the resulting files with "Prep/DemChop/demchop"
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3. 30-arcsec world wide data: GTOPO30 data:
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http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html
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a) First convert the "bin" DEM format to "ascii" DEM format using
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"Prep/DemRaw2ascii/raw2ascii"
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b) Then process the resulting files with "Prep/DemChop/demchop"
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4. SRTM (1 and 3-arcsec nearly world wide coverage):
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ftp://edcsgs9.cr.usgs.gov/pub/data/srtm/
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a) Chop up the .zip files using "Prep/DemChop/hgtchop"
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5. 3-arcsec ASCII DEM files:
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Generally, I recommend using the SRTM data over this older data
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set, however in places like Alaska, there is no SRTM coverage so
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this data is better than the 30 arcsec data.
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http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
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a) Create the .arr.gz files using the "Prep/DemChop/demchop" utility.
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The result for any of these terrain sources should be a "work" tree
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with a .arr.gz file for each FG tile.
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6. After you create the .arr.gz files you have to create a
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corresponding .fit.gz file for each of these. This is a data
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reduction step which fits a set of polygons to the raw terrain with
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a set of constraints on the maximum error allowed relative to the
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original data set, and a max/min number of allowed nodes in the
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fitted set. The provided tools use a scheme that produces an
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adaptive fit which means fewer polygons in smooth flat areas, and
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more polygons in complex rough areas. The end result is a *much*
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better fit with fewer polygons than you could achieve by just keeping
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every "nth" point from the original array.
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To walk through an entire tree of .arr.gz files and produce the
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corresponding .fit.gz files, use the "Prep/TerraFit/terrafit.py"
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utility. Please ignore the old "ArrayFit" tools which use a stupid
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algorithm and are basically useless in comparison to TerraFit.
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You should now have a large tree of .arr.gz files with a corresponding
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.fit.gz file for each .arr.gz file. It's worth double checking the
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contents of your directory and counting all files of each type to make
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sure you do have a one to one match and didn't miss anything.
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Generating Airports
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===================
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Robin Peel maintains a world wide database of airports and navaids for
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the X-Plane and FlightGear projects:
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http://www.x-plane.org/users/robinp/
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Robin's apt.dat needs to be run through two scripts
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cat apt.dat | ./xp2simpleapt.pl > basic.dat
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cat apt.dat | ./xp2runway.pl > runways.dat
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Compress these and copy them to $FG_ROOT/data/Airports
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Now run the runways.dat through the getapt utility:
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genapts --input=runways.dat --work=$FG_WORK_DIR
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Note: this creates a last_apt file which shows you the airport genapts
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is currently working on.
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- if genapts crashes (which is possible if you try to run through the
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entire runways.dat file) you can look at last_apt to see where to start
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up again.
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- You can start in midstream using the --start-id=KABC option to genapts.
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- If you get a consistant crash on a particular airport, you probably
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found a bug in genapts, or there is some degenerate information at that
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airport (40 mile long runways, 2 runways spaced miles apart, etc.)
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Often you can fix the data and proceed. Sometimes you can "nudge"
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things around to get past a genapts bug. For instance, if you crahs
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consistantly on a valid looking runway, try nudging the heading or
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position by a least significant digit. Sometimes we can get numerical
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problems with the polygon cliper and this often works around it.
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Other considerations:
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- Airport generation pre-depends on terrain data being preped and ready
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so airport surfaces can be built properly.
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- If you prep new terrain data, you should probably rerun the airport
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generation step.
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