Scenery:Terrain.cfg File - Revision history

129.240.228.21 at 11:13, 6 March 2007

2007-03-06T11:13:43Z

← Older revision		Revision as of 11:13, 6 March 2007
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	~~\section{~~Terrain configuration file}		==Terrain configuration file==

	This file is the main configuration for a terrain block. By		This file is the main configuration for a terrain block. By

129.240.228.21 at 11:13, 6 March 2007

2007-03-06T11:13:09Z

← Older revision		Revision as of 11:13, 6 March 2007
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	following example we look at a block of the Alps.		following example we look at a block of the Alps.

	~~\begin{verbatim}~~		<pre>
	# Common section		# Common section
	tile_size_n = 1920		tile_size_n = 1920
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	# Terrain generator section		# Terrain generator section
	tolerance = 1.5		tolerance = 1.5
	~~\end{verbatim}~~		</pre>

	~~\subsection{~~Terrain area section}		==Terrain area section==
	The first section describes the area of this terrain block. The		The first section describes the area of this terrain block. The
	\texttt{tile\_size} parameters determine the size of each tile in the		\texttt{tile\_size} parameters determine the size of each tile in the
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	equal and power of two.		equal and power of two.

	~~\subsection{~~Data input section}		==Data input section==
	The next section contains a few common parameters and a set of blocks		The next section contains a few common parameters and a set of blocks
	determining the input elevation data for terrain model.		determining the input elevation data for terrain model.
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	use SRTM data with 90m grid spacing, i.e the cell size is set to 90m.		use SRTM data with 90m grid spacing, i.e the cell size is set to 90m.

	~~\subsection{~~Data input blocks}		==Data input blocks==
	To create a terrain model we need at least one set of input elevation		To create a terrain model we need at least one set of input elevation
	data. These data sets are usually given as regular grids (raster) of		data. These data sets are usually given as regular grids (raster) of
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	\end{table}		\end{table}

	~~\subsubsection{~~Supported file formats}		===Supported file formats===
	The GeoGFX terrain generator supports a variety of input data		The GeoGFX terrain generator supports a variety of input data
	formats as shown in the following table.		formats as shown in the following table.
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	form, i.e \texttt{.hgt.gz} or \texttt{.dem.gz}.		form, i.e \texttt{.hgt.gz} or \texttt{.dem.gz}.

	~~\subsubsection{~~Projections}		===Projections===
	Some of the file formats have their projection data given in the data		Some of the file formats have their projection data given in the data
	file. However, some of the file formats contain no projection		file. However, some of the file formats contain no projection
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	an ASCIIGRID input file in UTM Zone 33 projection, WGS84 datum must be		an ASCIIGRID input file in UTM Zone 33 projection, WGS84 datum must be
	specified like this:		specified like this:
	~~\begin{verbatim}~~
			<pre>
	input_dir {		input_dir {
	path = /data/geodata/Norge/dted100m		path = /data/geodata/Norge/dted100m
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	coosys = +proj=utm +zone=33 +datum=WGS84		coosys = +proj=utm +zone=33 +datum=WGS84
	}		}
			</pre>

	~~\end{verbatim}~~
	Unprojected data (geographical lat/lon coordinates) in WGS84 datum		Unprojected data (geographical lat/lon coordinates) in WGS84 datum
	need no projection information.		need no projection information.

	~~\subsection{~~Terrain generator parameters}		==Terrain generator parameters==
	The last section is where you set the input for the terrain surface		The last section is where you set the input for the terrain surface
	generator. The only parameter here at the moment is the		generator. The only parameter here at the moment is the

129.240.228.21: New page: \section{Terrain configuration file} This file is the main configuration for a terrain block. By convention, this file is usually named \texttt{terrain.cfg}. In the following example we l...

2007-03-06T11:09:41Z

New page: \section{Terrain configuration file} This file is the main configuration for a terrain block. By convention, this file is usually named \texttt{terrain.cfg}. In the following example we l...

New page

\section{Terrain configuration file}

This file is the main configuration for a terrain block. By
convention, this file is usually named \texttt{terrain.cfg}. In the
following example we look at a block of the Alps.

\begin{verbatim}
# Common section
tile_size_n = 1920
tile_size_e = 1920
start_n = 43.5
start_e = 5.5
ref_lat = 50.0
num_tiles_n = 64
num_tiles_e = 64

# Data Reader section
img_cache_sz = 200
cell_size = 90
input_dir {
path = /exthd/geodata/srtm30
ext = .DEM.gz
pri = 0
}

input_dir {
path = /exthd/geodata/Alps/srtm
ext = .hgt
pri = 1
}

# Terrain generator section
tolerance = 1.5
\end{verbatim}

\subsection{Terrain area section}
The first section describes the area of this terrain block. The
\texttt{tile\_size} parameters determine the size of each tile in the
terrain, in meters. The size in east direction depends on the latitude
of the tile as described in the previous section, so this size is only
correct on the reference latitude given by \texttt{ref\_lat}.

Usually we recommend setting the tile size equal in east and north
directions. Usually we select a size which matches the highest
resolution textures available for the terrain block. In this example
we have 15m/pixel textures of 128$\times$128 pixels, which gives tile a size
of $15 \times 128 = 1920m$.

Next we have the lower left corner of the block given in decimal
degrees, in this case 43.5\degrees N and 5.5\degrees E. The reference
latitude \texttt{ref\_lat} is set to 50\degrees N.

The \texttt{num\_tiles} parameters determine the number of tiles in
each direction. As mentioned above, these values should normally be
equal and power of two.

\subsection{Data input section}
The next section contains a few common parameters and a set of blocks
determining the input elevation data for terrain model.

The first common parameter is \texttt{img\_cache\_size} which sets the
maximum amount of memory (in Mb) used by the data reader. If you have
a lot of memory you can set this quite high to increase the efficiency
of the data reader process.

The other common parameters is \texttt{cell\_size}. This parameter
determines the maximum resolution of the input data. In our case we
use SRTM data with 90m grid spacing, i.e the cell size is set to 90m.

\subsection{Data input blocks}
To create a terrain model we need at least one set of input elevation
data. These data sets are usually given as regular grids (raster) of
elevation values. Each data set is described by a \texttt{data\_dir}
block, enclosed in curly brackets, \texttt{\{} and \texttt{\}}.

In our example we have two input data sets, a coarse 1km grid taken
from the global SRTM30 data set, and the more detailed 90m grid, taken
from the main SRTM data set. \footnote{For more info on the SRTM data
sets, see \texttt{http://www2.jpl.nasa.gov/srtm/}}.

These data sets are prioritized with the \texttt{pri} parameter so
that the higher detailed SRTM data set has higher priority than the
SRTM30 data set. This means that if we have coverage from both data
sets in an area, the highest priority data set is used. The
\texttt{path} parameter is the full file path to the directory
containing the input data files, and the \texttt{ext} parameter is the
filename extension of the data files. All files in the directory with
this extension will be used.

The following table describes all valid parameters in a data set block.

\begin{table}[htbp]
\begin{center}
\begin{tabular}{ l p{6.5cm} }
\hline
\texttt{path = <file path>} & Full path to input data directory.\\
\texttt{ext = <n>} & File name extension of data files. (See below) \\
\texttt{pri = <n>} & Priority of data set. Higher values mean higher
priority.\\
\texttt{recursive = <true|false>} & If true, all subdirectories of
\texttt{path} will be checked for data files.\\
\texttt{coosys = <proj4 def.>} & Coordinate system and projection as a
used in the PROJ4 package (see below).\\\hline
\end{tabular}
\end{center}
\end{table}

\subsubsection{Supported file formats}
The GeoGFX terrain generator supports a variety of input data
formats as shown in the following table.
\begin{table}[htbp]
\begin{center}
\begin{tabular}{ l p{6.5cm} }
\hline
\texttt{.tif} & Either GeoTIFF or regular TIFF files with an ArcView
type ``world'' file, \texttt{.tfw}\\
\texttt{.asc} & ArcInfo ASCIIGRID format.\\
\texttt{.dt1} & DTED Level1 fomat.\\
\texttt{.hgt} & Raw SDTS format.\\
\texttt{.dem} & USGS DEM format or GTOPO30 DEM files.\\
\texttt{.ddf, tar, tgz} & USGS SDTS DEM file. These data sets can be
accessed directly from their tar archives for convenience.\\
\texttt{.bil} & Band-interleaved raw data files.\\\hline
\end{tabular}
\end{center}
\end{table}

Some of these data formats can also be stored in gzipped
form, i.e \texttt{.hgt.gz} or \texttt{.dem.gz}.

\subsubsection{Projections}
Some of the file formats have their projection data given in the data
file. However, some of the file formats contain no projection
information, so this must be specified in the data block. GeoGFX supports all projections and datums supported by the PROJ4
projection package (\texttt{http://proj.maptools.org/}). For example,
an ASCIIGRID input file in UTM Zone 33 projection, WGS84 datum must be
specified like this:
\begin{verbatim}
input_dir {
path = /data/geodata/Norge/dted100m
ext = .asc
coosys = +proj=utm +zone=33 +datum=WGS84
}

\end{verbatim}
Unprojected data (geographical lat/lon coordinates) in WGS84 datum
need no projection information.

\subsection{Terrain generator parameters}
The last section is where you set the input for the terrain surface
generator. The only parameter here at the moment is the
\texttt{tolerance} parameter. This is the maximum allowed vertical
distance between the generated terrain model and the original
data. I.e if you select 1.5m here, the maximum error in the surface
will be 1.5 meters relative to the input data set. The lower this
tolerance is, the larger the terrain file will be. It's usually wise
to set this at a number between 1 and 5 meters to keep file size down,
while still retaining good accuracy.

[[Category:Scenery]]