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Add description of cliff generation; remove debugging printout.

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James.Hester 2018-12-31 11:16:16 +11:00
parent e8b87fcf74
commit 5586be95f5
2 changed files with 55 additions and 9 deletions
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54
README.howto
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@ -1,5 +1,6 @@
Original version by Alexei Novikov <anovikov@heron.itep.ru> Sep. 3, 1999
Updates by Curtis Olson <http://www.flightgear.org/~curt>
Cliff description by James Hester 2018
Overview
@ -120,3 +121,56 @@ tg-construct-client in rude mode. After a while scenery is ready.
That's all folks,
Alexei.
Addendum: Adding cliffs
=======================
Cliffs represent discontinuities in the height array described above. This
is problematic because:
(1) Most height grids will give an average height in the area around the
grid
(2) Interpolation between grid points to get the local height will convert
a cliff into a much more gentle slope.
To add cliffs into the scenery using OpenStreetMap data, the following
approach can be used:
(1) Extract cliffs from the OSM datafile using your favourite
tool, for example for all cliffs near Sydney, Australia:
osmosis --read-pbf australia-latest.osm.pbf --bounding-box top=-33 left=150
bottom=-35 right=152 completeWays=yes --lp --tf accept-ways 'natural=cliff'
--tf reject-relations --used-node --write-xml file='my_cliffs.osm'
(2) Convert the XML above to Shapefiles:
ogr2ogr -where "OGR_GEOMETRY='LineString'" -f 'ESRI shapefile' -lco SHPT=ARC
cs_cliffs my_cliffs.osm
(3) Run cliff-decode to place cliff information into the height grid working
directory created previously (<data>/cs_cliffs in the example below):
cliff-decode <work_base>/SRTM-3 <data>/cs_cliffs
(4) Optionally run rectify_height to fix grid heights. This is recommended
as otherwise cliffs will have uneven edges and bases as the grid points
vary in distance from the cliff:
rectify_height --work-dir=<work_base> --height-dir=SRTM-3 --min-lon=151.0
--max-lon=152.0 --min-lat=-34.0 --max-lat=-33.0 --min-dist=100
The min-dist parameter sets the distance from the cliff beyond which points
are trustworthy. 100m is the default.
(5) Place the cliffs into the scenery. This is identical to the process for
rivers and roads and uses the same cliff information from step (2):
ogr-decode --line-width 5 --area-type Rock <work_base>/Cliffs <data>/cs_cliffs"
Note that an area-type of Cliffs will allow custom cliff texturing, if this
effect is available. This command places a 5m wide strip of rock at the
position of the cliffs. One side of this strip will have a calculated elevation
at the top of the cliff, and the other will be at the bottom.
(6) Run tg-construct as usual, including 'Rock' or 'Cliffs' polygon types to
make sure that cliffs appear.

10
src/Lib/terragear/tg_chopper.cxx
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@ -24,15 +24,7 @@ tgPolygon tgChopper::Clip( const tgPolygon& subject,
result = tgPolygon::Intersect( subject, base);
// Debug: See if numbers of nodes have changed
if ( result.Contours() > 0 ) {
/*if (result.ContourSize(0) != subject.ContourSize(0)) {
tgRectangle rr = subject.GetBoundingBox();
SG_LOG(SG_GENERAL,SG_INFO,"---- Bucket ID " << b.gen_index() << " ------- " );
SG_LOG(SG_GENERAL,SG_INFO,"A contour has changed size");
SG_LOG(SG_GENERAL,SG_INFO,"Bounding box " << rr.getMin() << " , " << rr.getMax() );
SG_LOG(SG_GENERAL,SG_INFO,"Old size " << subject.ContourSize(0) << " New size " << result.ContourSize(0));
SG_LOG(SG_GENERAL,SG_INFO,"Old: First node " << subject.GetNode(0,0) << " New: First node " << result.GetNode(0,0));
SG_LOG(SG_GENERAL,SG_INFO,"Clipping rectangle: " << base.GetContour(0));
}*/
if ( subject.GetPreserve3D() ) {
result.InheritElevations( subject );
result.SetPreserve3D( true );