170 lines
No EOL
6.8 KiB
Text
170 lines
No EOL
6.8 KiB
Text
Original version by Alexei Novikov <anovikov@heron.itep.ru> Sep. 3, 1999
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Updates by Curtis Olson <http://www.flightgear.org/~curt>
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Cliff description by James Hester 2018
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Overview
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========
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The scenery creation process has 3 basic steps. 1. Fetch the raw
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data. 2. Preprocess this data into an intermediate form. 3.
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Assemble the intermediate data into the final scenery tiles.
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There are a couple basic types of data used to create scenery. 1. DEM
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data which is typically a set of elevation points on a regular grid.
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2. Polygonal data such as landmass outlines, lakes, urban areas,
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glaciers, etc. 3. Other more specialized data such as airport
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runways and taxiways, lighthouse locations, etc.
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Preparation and Preprocessing
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============================
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1) DEM data.
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As the first step you have to download DEM for the area you need. (You
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can get them from USGS site).
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Then you have to chop files that we got into the tiles used for the
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scenery generation. You should use hgtchop for this. As we already have
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a number of files I'm using the following Perl script
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#--------------------------------------------------------------------------
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#!/usr/bin/perl
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my @files=glob("./*.hgt");
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my $size=@files;
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for (my $i=0;$i<$size;$i++) {
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system("hgtchop $files[$i] /home/anovikov/w020n90/Work/SRTM-3");
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}
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#--------------------------------------------------------------------------
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Here you can change /home/anovikov/w020n90 to whatever you like but keep
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in mind that we will use that directory for our scenery generation.
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The 3 arcsec DEMs (which are available for the USA) should go in
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.../Work/DEM-3/
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That's all with the DEM files. If yu want to have a blibloagraphy on
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them see f.e. http://www.geo.ed.ac.uk/geoinfo/dem.send
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2) Airport Data
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Next thing is to generate airports data. You need to have default.apt
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from the fgfs-base package and genapts compiled. Usage is genapts
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/path/to/appt_file /work/dir (in our example
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genapts .../RawData/AirNa/default.apt.gz .../Work/Airports/
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3) Landmass Data
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You can just download it from Curtis FTP site
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ftp://kenai.me.umn.edu/pub/fgfs/RawData/Global-Landmass/
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or generate it by yourself. If you download data from Curtis site then
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you should extract it in the .../Work/Global-Landmass
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If you are generating it by yourself you have to ask Curtis how he is
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doing that.
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4) Landuse Data. (Curtis, you asked me for this).
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If you have a CD-ROM with DCW then you are lucky, if not you need to go
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to ESRI WWW site (http://www.esri.com/data/online/index.html), "Select
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by Geographic Area" - "Esri Thematic Data" (Go!) then
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Select a Theme - Natural Landscape Zones, Select a Region - Continent
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you need and download data. Please read the license agreement first.
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Then comes the tricky part. (You will need to modify the code)
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I included one file you have to change as an attachment . You have to
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put it in /FlightGear/Tools/Lib/Polygon/ rebuild the libPolygon and
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then change the shape-decode. Go to /FlightGear/Tools/Prep/ShapeFile/
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open main.cxx and either comment out line # 357 or add || area ==
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DefaultArea at line #279.
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Then you have to rebuild the shape-decode. Now we are ready to generate
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the landuse data.
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./shapedecode /name/of_the_file_from_esri /work_dir/work.states
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(in my case it is ./shapedecode /users/anovikov/fgfs_data/aalandsc
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/home/anovikov/w020n90/work.states).
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5) Hydro and Urban data.
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Origianlly I was using the same ESRI web server but this is kind of very
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tricky part that I will not tell you. (I was writing about the way to do
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it in the mailing list)
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I think that one can get data from Coastline Extractor using "Rivers
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from WDBII" but I'm not 100% sure.
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If you have acess to DCW then you just run shapedecode on the
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corresponding files puting hydro data in the directory work.hydro and
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urban data in the directory work.urban.
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As Curtis changed the directory structure in the last CVS versions you
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have to look in BuildTiles/Main/main.cxx first and modify the directory
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names accordingly. (FE 30 arc-sec files should be in work_base/DEM-30/
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Now we finished with data preparation and we can start generating
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scenery but first we need to change the resolution of the data from the
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default values ( if we are working with 30 arc sec DEMs). You have to
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find line
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double error = 200.0 in Construct/Main/main.cxx and change initial error
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to smth like 10. Then you need to rebuild everything in that directory.
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I generally hate using tg-launch-clients and tg-launch-server so I'm
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doing everyting (almost) by hand. So I start from Construct/Parallel
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launch tg-construct-server on the computer with data on local disk and
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then slogin to other computers ( with data mounted over nfs) and run
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tg-construct-client in rude mode. After a while scenery is ready.
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That's all folks,
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Alexei.
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Addendum: Adding cliffs
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=======================
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Cliffs represent discontinuities in the height array described above. This
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is problematic because:
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(1) Most height grids will give an average height in the area around the
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grid
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(2) Interpolation between grid points to get the local height will convert
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a cliff into a much more gentle slope.
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To add cliffs into the scenery using OpenStreetMap data, the following
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approach can be used:
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(1) Extract cliffs from the OSM datafile using your favourite
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tool, for example for all cliffs near Sydney, Australia:
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osmosis --read-pbf australia-latest.osm.pbf --bounding-box top=-33 left=150
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bottom=-35 right=152 completeWays=yes --lp --tf accept-ways 'natural=cliff'
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--tf reject-relations --used-node --write-xml file='my_cliffs.osm'
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(2) Convert the XML above to Shapefiles:
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ogr2ogr -where "OGR_GEOMETRY='LineString'" -f 'ESRI shapefile' -lco SHPT=ARC
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cs_cliffs my_cliffs.osm
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(3) Run cliff-decode to place cliff information into the height grid working
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directory created previously (<data>/cs_cliffs in the example below):
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cliff-decode <work_base>/SRTM-3 <data>/cs_cliffs
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(4) Optionally run rectify_height to fix grid heights. This is recommended
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as otherwise cliffs will have uneven edges and bases as the grid points
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vary in distance from the cliff:
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rectify_height --work-dir=<work_base> --height-dir=SRTM-3 --min-lon=151.0
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--max-lon=152.0 --min-lat=-34.0 --max-lat=-33.0 --min-dist=100
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The min-dist parameter sets the distance from the cliff beyond which points
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are trustworthy. 100m is the default.
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(5) Place the cliffs into the scenery. This is identical to the process for
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rivers and roads and uses the same cliff information from step (2):
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ogr-decode --line-width 5 --area-type Rock <work_base>/Cliffs <data>/cs_cliffs"
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Note that an area-type of Cliffs will allow custom cliff texturing, if this
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effect is available. This command places a 5m wide strip of rock at the
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position of the cliffs. One side of this strip will have a calculated elevation
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at the top of the cliff, and the other will be at the bottom.
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(6) Run tg-construct as usual, including 'Rock' or 'Cliffs' polygon types to
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make sure that cliffs appear. |