frmt_various.html

gdal库的学习文档

.HD. <p>

The NDF driver only supports 8bit data.  The only supported projection is
UTM.  NDF version 1 (NDF_VERSION=0.00) and NDF version 2 are both supported.
<p>

NOTE: Implemented as <tt>gdal/frmts/raw/ndfdataset.cpp</tt>.<p>

See Also: <a href="http://landsat.usgs.gov/documents/NLAPSII.pdf">NLAPS
Data Format Specification</a>.<p>					

<h2><a name="GMT">GMT -- GMT Compatible netCDF</a></h2>

GDAL has limited support for reading and writing netCDF <i>grid</i> files. 
NetCDF files that are not recognised as grids (they lack variables called
dimension, and z) will be silently ignored by this driver.  This driver is
primarily intended to provide a mechanism for grid interchange with the 
<a href="http://gmt.soest.hawaii.edu/">GMT</a> package.  The 
netCDF driver should be used for more general netCDF datasets.<p>

The units information in the file will be ignored, but x_range, and
y_range information will be read to get georeferenced extents of the raster.
All netCDF data types should be supported for reading.

Newly created files (with a type of <tt>GMT</tt>) will always have
units of "meters" for x, y and z but the x_range, y_range and z_range should 
be correct.  Note that netCDF does not have an unsigned byte data type, so 
8bit rasters will generally need to be converted to Int16 for export to 
GMT.<p>

NetCDF support in GDAL is optional, and not compiled in by default.  <p>

NOTE: Implemented as <tt>gdal/frmts/netcdf/gmtdataset.cpp</tt>.<p>

See Also: <a href="http://www.unidata.ucar.edu/packages/netcdf/">Unidata NetCDF Page</a><p>

<h2><a name="netCDF">netCDF -- Network Common Data Format</a></h2>

GDAL has limited support for reading general netCDF files.<p>

NetCDF support in GDAL is optional, and not compiled in by default.<p>

NOTE: Implemented as <tt>gdal/frmts/netcdf/netcdfdataset.cpp</tt>.<p>

See Also: <a href="http://www.unidata.ucar.edu/packages/netcdf/">Unidata NetCDF Page</a><p>

<h2><a name="PAux">PAux -- PCI .aux Labelled Raw Format</a></h2>

GDAL includes a partial implementation of the PCI .aux labelled raw raster 
file for read, write and creation.  To open a PCI labelled file, select the
raw data file itself.  The .aux file (which must have a common base name) will
be checked for automatically. <p>

The format type for creating new files is <tt>PAux</tt>.  All PCI data types
(8U, 16U, 16S, and 32R) are supported.  Currently georeferencing, projections, 
and other metadata is ignored.<p>

NOTE: Implemented as <tt>gdal/frmts/raw/pauxdataset.cpp</tt>.<p>

See Also: <a href="http://www.pcigeomatics.com/cgi-bin/pcihlp/GDB|Supported+File+Formats|Raw+Binary+Image+Format+(RAW)|Raw+.aux+Format">PCI's .aux Format
Description</a><p>

<h2><a name="PCRaster">PCRaster raster file format</a></h2>
<p>GDAL includes support for reading and writing PCRaster raster files. PCRaster is a dynamic modelling system for distributed simulation models. The main applications of PCRaster are found in environmental modelling: geography, hydrology, ecology to name a few. Examples include rainfall-runoff models, vegetation competition models and slope stability models.</p>

<p>The driver reads all types of PCRaster maps: booleans, nominal, ordinals, scalar, directional and ldd. The same cell representation used to store values in the file is used to store the values in memory.</p>

<p>The driver detects whether the source of the GDAL raster is a PCRaster file. When such a raster is written to a file the value scale of the original raster will be used. The driver <b>always</b> writes values using UINT1, INT4 or REAL4 cell representations, depending on the value scale:</p>

<table>
  <thead>
    <tr>
      <th>Value scale</th>
      <th>Cell representation</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>VS_BOOLEAN</td>
      <td>CR_UINT1</td>
    </tr>
    <tr>
      <td>VS_NOMINAL</td>
      <td>CR_INT4</td>
    </tr>
    <tr>
      <td>VS_ORDINAL</td>
      <td>CR_INT4</td>
    </tr>
    <tr>
      <td>VS_SCALAR</td>
      <td>CR_REAL4</td>
    </tr>
    <tr>
      <td>VS_DIRECTION</td>
      <td>CR_REAL4</td>
    </tr>
    <tr>
      <td>VS_LDD</td>
      <td>CR_UINT1</td>
    </tr>
  </tbody>
</table>

<p>For rasters from other sources than a PCRaster raster file a value scale and cell representation is determined according to the folowing rules:</p>

<table>
  <thead>
    <tr>
      <th>Source type</th>
      <th>Target value scale</th>
      <th>Target cell representation</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>GDT_Byte</td>
      <td>VS_BOOLEAN</td>
      <td>CR_UINT1</td>
    </tr>
    <!--
    <tr>
      <td>GDT_UInt16</td>
      <td>VS_NOMINAL</td>
      <td>CR_UINT1</td>
    </tr>
    <tr>
      <td>GDT_UInt32</td>
      <td>VS_NOMINAL</td>
      <td>CR_UINT1</td>
    </tr>
    <tr>
      <td>GDT_Int16</td>
      <td>VS_NOMINAL</td>
      <td>CR_INT4</td>
    </tr>
    -->

    <tr>
      <td>GDT_Int32</td>
      <td>VS_NOMINAL</td>
      <td>CR_INT4</td>
    </tr>
    <tr>
      <td>GDT_Float32</td>
      <td>VS_SCALAR</td>
      <td>CR_REAL4</td>
    </tr>
    <tr>
      <td>GDT_Float64</td>
      <td>VS_SCALAR</td>
      <td>CR_REAL4</td>
    </tr>
  </tbody>
</table>

<p>The driver can convert values from one supported cell representation to another. It cannot convert to unsupported cell representations. For example, it is not possible to write a PCRaster raster file from values which are used as CR_INT2 (GDT_Int16).

<p>NOTE: Implemented as <tt>gdal/frmts/pcraster/pcrasterdataset.cpp</tt>.</p>

See also: <a href="http://pcraster.geog.uu.nl">PCRaster website at Utrecht University</a> and <a href="http://www.pcraster.nl">PCRaster Environmental Software company website</a>.

<h2><a name="PNG">PNG -- Portable Network Graphics</a></h2>

GDAL includes support for reading, and creating .png files.  Greyscale, 
pseudo-colored, Paletted, RGB and RGBA PNG files are supported as well as 
precisions of eight and sixteen bits per sample.<p>

PNG files are linearly compressed, so random reading of large PNG files can
be very inefficient (resulting in many restarts of decompression from the
start of the file).<p>

Text chunks are translated into metadata, typically with multiple lines per
item.  <a href="#WLD">World files</a> with the extensions of .wld, .tfw or
.tifw will be read.  Single transparency values in greyscale files will be
recognised as a nodata value in GDAL.  Transparent index in paletted images
are preserved when the color table is read. <p>

PNG files can be created with a type of PNG, using the CreateCopy() method, 
requiring a prototype to read from.  Writing includes support for the
various image types, and will preserve transparency/nodata values.  
Georeferencing .wld files are written if option WORLFFILE setted.  All
pixel types other than 16bit unsigned will be written as eight bit.<p>

Creation Options:<p>

<ul>

<li> <b>WORLDFILE=YES</b>: Force the generation of an associated ESRI world
file (with the extension .wld). See <a href="#WLD">World File</a> section for
details.
<p>
</ul>

NOTE: Implemented as <tt>gdal/frmts/png/pngdataset.cpp</tt>.<p> 

PNG support is implemented based on the libpng reference library.  
More information is available at <a href="http://www.libpng.org/pub/png">
http://www.libpng.org/pub/png</a>.<p>

<h2><a name="PNM">PNM -- Netpbm (.pgm, .ppm)</a></h2>

GDAL includes support for reading, and creating .pgm (greyscale), and
.ppm (RGB color) files compatible with the Netpbm tools.  Only the binary
(raw) formats are supported.<p>

Netpbm files can be created with a type of PNM.<p>

Creation Options:<p>

<ul>

<li> <b>MAXVAL=n</b>: Force setting the maximum color value to <B>n</B>
in the output PNM file. May be useful if you plannig use the output files with
software which is not liberal to this value.<p>
</ul>

NOTE: Implemented as <tt>gdal/frmts/raw/pnmdataset.cpp</tt>. 

<h2><a name="SAR_CEOS">SAR_CEOS -- CEOS SAR Image</a></h2>

This is a read-only reader for CEOS SAR image files.  To use, select
the main imagery file.<p>

This driver works with most Radarsat and ERS data
products, including single look complex products; however, it is unlikely
to work for non-Radar CEOS products.  The simpler <a href="#CEOS">CEOS</a>
driver is often appropriate for these.<p>

This driver will attempt to read 15 lat/long GCPS by sampling the per-scanline
CEOS superstructure information.  It also captures various pieces of metadata
from various header files, including:<p>

<pre>
  CEOS_LOGICAL_VOLUME_ID=EERS-1-SAR-MLD  
  CEOS_PROCESSING_FACILITY=APP         
  CEOS_PROCESSING_AGENCY=CCRS    
  CEOS_PROCESSING_COUNTRY=CANADA      
  CEOS_SOFTWARE_ID=APP 1.62    
  CEOS_ACQUISITION_TIME=19911029162818919               
  CEOS_SENSOR_CLOCK_ANGLE=  90.000
  CEOS_ELLIPSOID=IUGG_75         
  CEOS_SEMI_MAJOR=    6378.1400000
  CEOS_SEMI_MINOR=    6356.7550000
</pre>

The SAR_CEOS driver also includes some support for SIR-C and PALSAR 
polarimetric data.  The SIR-C format contains an image in compressed
scattering matrix form, described 
<a href="http://southport.jpl.nasa.gov/software/dcomp/dcomp.html">here</a>.  
GDAL decompresses the data as it is read in.  The PALSAR format
contains bands that correspond almost exactly to elements of the 3x3
Hermitian covariance matrix-
see the <a href="http://www.ersdac.or.jp/palsar/palsar_E.html">
ERSDAC-VX-CEOS-004A.pdf</a> document for a complete description (pixel 
storage is described on page 193). GDAL converts these to complex floating
point covariance matrix bands as they are read in.  The convention used
to represent the covariance matrix in terms of the scattering matrix
elements HH, HV (=VH), and VV is indicated below. Note that the 
non-diagonal elements of the matrix are complex values, while the diagonal
values are real (though represented as complex bands).<p> 

<ul>
<li> Band 1: Covariance_11 (Float32) = HH*conj(HH)
<li> Band 2: Covariance_12 (CFloat32) = sqrt(2)*HH*conj(HV)
<li> Band 3: Covariance_13 (CFloat32) = HH*conj(VV)
<li> Band 4: Covariance_22 (Float32) = 2*HV*conj(HV)
<li> Band 5: Covariance_23 (CFloat32) = sqrt(2)*HV*conj(VV)
<li> Band 6: Covariance_33 (Float32) = VV*conj(VV)
</ul>


The identities of the bands are also reflected in the metadata.  <p>

NOTE: Implemented as <tt>gdal/frmts/ceos2/sar_ceosdataset.cpp</tt>.<p>

<h2><a name="SDTS">SDTS -- USGS SDTS DEM</a></h2>

GDAL includes support for reading USGS SDTS formatted DEMs.  USGS DEMs are
always returned with a data type of signed sixteen bit integer, or 32bit float.
Projection and georeferencing information is also returned.<p>

SDTS datasets consist of a number of files.  Each DEM should have one file
with a name like XXXCATD.DDF.  This should be selected to open
the dataset.<p>

The elevation units of DEMs may be feet or meters.  The GetType() method on a 
band will attempt to return if the units are Feet ("ft") or Meters ("m").

NOTE: Implemented as <tt>gdal/frmts/sdts/sdtsdataset.cpp</tt>.<p>

<h2><a name="SGI">SGI - SGI Image Format</a></h2>

The SGI driver currently supports the reading of SGI Image files.<p>

The driver currently supports 1, 2, 3, and 4 band images. The driver 
currently supports "8 bit per channel value" images. The driver supports 
both uncompressed and run-length encoded (RLE) images.<p>

The GDAL SGI Driver was based on Paul Bourke's SGI image read code.<p>

The driver does not currently have any image creation capabilities.<p>

See Also:<p>

<ul>
<li> <a href="http://astronomy.swin.edu.au/~pbourke/dataformats/sgirgb/">Paul Bourke's SGI Image Read Code</a>
<li> <a href="ftp://ftp.sgi.com/graphics/SGIIMAGESPEC">SGI Image File Format Document </a>
</ul>

NOTE: Implemented as <tt>gdal/frmts/sgi/sgidataset.cpp</tt>.<p>

<h2><a name="WLD">WLD -- ESRI World File</a></h2>

A world file file is a plain ASCII text file consisting of six values separated
by newlines.  The format is: <br>

<pre>
 pixel X size
 rotation about the Y axis (usually 0.0)
 rotation about the X axis (usually 0.0)
 negative pixel Y size
 X coordinate of upper left pixel center
 Y coordinate of upper left pixel center
</pre>

For example: <br>

<pre>
60.0000000000
0.0000000000
0.0000000000
-60.0000000000
440750.0000000000
3751290.0000000000
</pre>

You can construct that file simply by using your favorite text editor.<p>

World file usually has suffix .wld, but sometimes it may has .tfw, tifw, .jgw
or other suffixes depending on the image file it comes with.<p>

<h2><a name="XPM">XPM - X11 Pixmap</a></h2>

GDAL includes support for reading and writing XPM (X11 Pixmap Format) 
image files.  These are colormapped one band images primarily used for 
simple graphics purposes in X11 applications.  It has been incorporated in
GDAL primarily to ease translation of GDAL images into a form useable with
the GTK toolkit.<p>

The XPM support does not support georeferecing (not available from XPM files)
nor does it support XPM files with more than one character per pixel.  New
XPM files must be colormapped or greyscale, and colortables will be reduced
to about 70 colors automatically.<p>

NOTE: Implemented as <tt>gdal/frmts/xpm/xpmdataset.cpp</tt>.<p>

<hr>
<p>
<a href="formats_list.html">Full list of GDAL Raster Formats</a>
</p>

<p>
$Id: frmt_various.html 10147 2006-10-24 17:36:47Z fwarmerdam $
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