NAME
gdal_grid - gdal_grid creates regular grid from the scattered data
SYNOPSIS
Usage: gdal_grid [--help-general] [--formats]
[-ot {Byte/Int16/UInt16/UInt32/Int32/Float32/Float64/
CInt16/CInt32/CFloat32/CFloat64}]
[-of format] [-co "NAME=VALUE"]
[-zfield field_name]
[-a_srs srs_def] [-spat xmin ymin xmax ymax]
[-l layername]* [-where expression] [-sql select_statement]
[-txe xmin xmax] [-tye ymin ymax] [-outsize xsize ysize]
[-a algorithm[:parameter1=value1]*] [-quiet]
<src_datasource> <dst_filename>
DESCRIPTION
This program creates regular grid (raster) from the scattered data read
from the OGR datasource. Input data will be interpolated to fill grid
nodes with values, you can choose from various interpolation methods.
-ot type:
For the output bands to be of the indicated data type.
-of format:
Select the output format. The default is GeoTIFF (GTiff). Use the
short format name.
-txe xmin xmax:
Set georeferenced X extents of output file to be created.
-tye ymin ymax:
Set georeferenced Y extents of output file to be created.
-outsize xsize ysize:
Set the size of the output file in pixels and lines.
-a_srs srs_def:
Override the projection for the output file. The srs_def may be any
of the usual GDAL/OGR forms, complete WKT, PROJ.4, EPSG:n or a file
containing the WKT.
-zfield field_name:
Identifies an attribute field on the features to be used to get a Z
value from. This value overrides Z value read from feature geometry
record (naturally, if you have a Z value in geometry, otherwise you
have no choice and should specify a field name containing Z value).
-a [algorithm[:parameter1=value1][:parameter2=value2]...]:
Set the interpolation algorithm or data metric name and
(optionally) its parameters. See INTERPOLATION ALGORITHMS and DATA
METRICS sections for further discussion of available options.
-spat xmin ymin xmax ymax:
Adds a spatial filter to select only features intersecting the
bounding box described by (xmin, ymin) - (xmax, ymax).
-l layername:
Indicates the layer(s) from the datasource that will be used for
input features. May be specified multiple times, but at least one
layer name or a -sql option must be specified.
-where expression:
An optional SQL WHERE style query expression to be applied to
select features to process from the input layer(s).
-sql select_statement:
An SQL statement to be evaluated against the datasource to produce
a virtual layer of features to be processed.
-co NAME=VALUE:
Passes a creation option to the output format driver. Multiple -co
options may be listed. See format specific documentation for legal
creation options for each format.
-quiet:
Suppress progress monitor and other non-error output.
src_datasource:
Any OGR supported readable datasource.
dst_filename:
The GDAL supported output file.
INTERPOLATION ALGORITHMS
There are number of interpolation algorithms to choose from.
invdist
Inverse distance to a power. This is default algorithm. It has
following parameters:
power:
Weighting power (default 2.0).
smoothing:
Smoothing parameter (default 0.0).
radius1:
The first radius (X axis if rotation angle is 0) of search ellipse.
Set this parameter to zero to use whole point array. Default is
0.0.
radius2:
The second radius (Y axis if rotation angle is 0) of search
ellipse. Set this parameter to zero to use whole point array.
Default is 0.0.
angle:
Angle of search ellipse rotation in degrees (counter clockwise,
default 0.0).
max_points:
Maximum number of data points to use. Do not search for more points
than this number. This is only used if search ellipse is set (both
radiuses are non-zero). Zero means that all found points should be
used. Default is 0.
min_points:
Minimum number of data points to use. If less amount of points
found the grid node considered empty and will be filled with NODATA
marker. This is only used if search ellipse is set (both radiuses
are non-zero). Default is 0.
nodata:
NODATA marker to fill empty points (default 0.0).
average
Moving average algorithm. It has following parameters:
radius1:
The first radius (X axis if rotation angle is 0) of search ellipse.
Set this parameter to zero to use whole point array. Default is
0.0.
radius2:
The second radius (Y axis if rotation angle is 0) of search
ellipse. Set this parameter to zero to use whole point array.
Default is 0.0.
angle:
Angle of search ellipse rotation in degrees (counter clockwise,
default 0.0).
min_points:
Minimum number of data points to use. If less amount of points
found the grid node considered empty and will be filled with NODATA
marker. Default is 0.
nodata:
NODATA marker to fill empty points (default 0.0).
Note, that it is essential to set search ellipse for moving average
method. It is a window that will be averaged when computing grid nodes
values.
nearest
Nearest neighbor algorithm. It has following parameters:
radius1:
The first radius (X axis if rotation angle is 0) of search ellipse.
Set this parameter to zero to use whole point array. Default is
0.0.
radius2:
The second radius (Y axis if rotation angle is 0) of search
ellipse. Set this parameter to zero to use whole point array.
Default is 0.0.
angle:
Angle of search ellipse rotation in degrees (counter clockwise,
default 0.0).
nodata:
NODATA marker to fill empty points (default 0.0).
DATA METRICS
Besides the interpolation functionality gdal_grid can be used to
compute some data metrics using the specified window and output grid
geometry. These metrics are:
minimum:
Minimum value found in grid node search ellipse.
maximum:
Maximum value found in grid node search ellipse.
range:
A difference between the minimum and maximum values found in grid
node search ellipse.
All the metrics have the same set of options:
radius1:
The first radius (X axis if rotation angle is 0) of search ellipse.
Set this parameter to zero to use whole point array. Default is
0.0.
radius2:
The second radius (Y axis if rotation angle is 0) of search
ellipse. Set this parameter to zero to use whole point array.
Default is 0.0.
angle:
Angle of search ellipse rotation in degrees (counter clockwise,
default 0.0).
min_points:
Minimum number of data points to use. If less amount of points
found the grid node considered empty and will be filled with NODATA
marker. This is only used if search ellipse is set (both radiuses
are non-zero). Default is 0.
nodata:
NODATA marker to fill empty points (default 0.0).
READING COMMA SEPARATED VALUES
Often you have a text file with a list of comma separated XYZ values to
work with (so called CSV file). You can easily use that kind of data
source in gdal_grid. All you need is create a virtual dataset header
(VRT) for you CSV file and use it as input datasource for gdal_grid.
You can find details on VRT format at Virtual Format description page.
Here is a small example. Let we have a CSV file called dem.csv
containing
Easting,Northing,Elevation
86943.4,891957,139.13
87124.3,892075,135.01
86962.4,892321,182.04
87077.6,891995,135.01
For above data we will create dem.vrt header with the following
content:
<OGRVRTDataSource>
<OGRVRTLayer name="dem">
<SrcDataSource>dem.csv</SrcDataSource>
<GeometryType>wkbPoint</GeometryType>
<GeometryField encoding="PointFromColumns" x="Easting" y="Northing" z="Elevation"/>
</OGRVRTLayer>
</OGRVRTDataSource>
This description specifies so called 2.5D geometry with three
coordinates X, Y and Z. Z value will be used for interpolation. Now you
can use dem.vrt with all OGR programs (start with ogrinfo to test that
everything works fine). The datasource will contain single layer called
dem filled with point features constructed from values in CSV file.
Using this technique you can handle CSV files with more than three
columns, switch columns, etc.
If your CSV file does not contain column headers then it can be handled
in the following way:
<GeometryField encoding="PointFromColumns" x="field_1" y="field_2" z="field_3"/>
Comma Separated Value description page contains details on CSV format
supported by GDAL/OGR.
EXAMPLE
The following would create raster TIFF file from VRT datasource
described in READING COMMA SEPARATED VALUES section using the inverse
distance to a power method. Values to interpolate will be read from Z
value of geometry record.
gdal_grid -a invdist:power=2.0:smoothing=1.0 -txe 85000 89000 -tye 894000 890000 -outsize 400 400 -of GTiff -ot Float64 -l dem dem.vrt dem.tiff
The next command does the same thing as the previos one, but reads
values to interpolate from the attribute field specified with -zfield
option instead of geometry record. So in this case X and Y coordinates
are being taken from geometry and Z is being taken from the Elevation
field.
gdal_grid -zfield "Elevation" -a invdist:power=2.0:smoothing=1.0 -txe 85000 89000 -tye 894000 890000 -outsize 400 400 -of GTiff -ot Float64 -l dem dem.vrt dem.tiff
AUTHORS
Andrey Kiselev <dron@ak4719.spb.edu>