gdal_grid - Creates regular grid from the scattered data.
gdal_grid [-ot {Byte/Int16/UInt16/UInt32/Int32/Float32/Float64/
CInt16/CInt32/CFloat32/CFloat64}]
[-of format] [-co "NAME=VALUE"]
[-zfield field_name] [-z_increase increase_value] [-z_multiply multiply_value]
[-a_srs srs_def] [-spat xmin ymin xmax ymax]
[-clipsrc <xmin ymin xmax ymax>|WKT|datasource|spat_extent]
[-clipsrcsql sql_statement] [-clipsrclayer layer]
[-clipsrcwhere expression]
[-l layername]* [-where expression] [-sql select_statement]
[-txe xmin xmax] [-tye ymin ymax] [-outsize xsize ysize]
[-a algorithm[:parameter1=value1]*] [-q]
<src_datasource> <dst_filename>
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.
Starting with GDAL 1.10, it is possible to set the
GDAL_NUM_THREADS configuration option to parallelize the processing.
The value to specify is the number of worker threads, or ALL_CPUS to
use all the cores/CPUs of the computer.
- -ot
type:
- For the output bands to be of the indicated data type.
- -of
format:
- Select the output format. Starting with GDAL 2.3, if not specified, the
format is guessed from the extension (previously was 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. No reprojection is done.
- -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).
- -z_increase
increase_value:
- Addition to the attribute field on the features to be used to get a Z
value from. The addition should be the same unit as Z value. The result
value will be Z value + Z increase value. The default value is 0.
- -z_multiply
multiply_value:
- This is multiplication ratio for Z field. This can be used for shift from
e.g. foot to meters or from elevation to deep. The result value will be (Z
value + Z increase value) * Z multiply value. The default value is 1.
- -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 contained within the
bounding box described by (xmin, ymin) - (xmax, ymax).
- -clipsrc
[xmin ymin xmax ymax]|WKT|datasource|spat_extent:
- Adds a spatial filter to select only features contained within the
specified bounding box (expressed in source SRS), WKT geometry (POLYGON or
MULTIPOLYGON), from a datasource or to the spatial extent of the
-spat option if you use the spat_extent keyword. When
specifying a datasource, you will generally want to use it in combination
of the -clipsrclayer, -clipsrcwhere or -clipsrcsql
options.
- -clipsrcsql
sql_statement:
- Select desired geometries using an SQL query instead.
- -clipsrclayer
layername:
- Select the named layer from the source clip datasource.
- -clipsrcwhere
expression:
- Restrict desired geometries based on attribute query.
- -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.
- -q:
- Suppress progress monitor and other non-error output.
- src_datasource:
- Any OGR supported readable datasource.
- dst_filename:
- The GDAL supported output file.
There are number of interpolation algorithms to choose from.
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 radii 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 radii are non-zero). Default is
0.
- nodata:
- NODATA marker to fill empty points (default 0.0).
(Since GDAL 2.1) Inverse distance to a power with nearest neighbor
searching, ideal when max_points is used. It has following parameters:
- power:
- Weighting power (default 2.0).
- smoothing:
- Smoothing parameter (default 0.0).
- radius:
- The radius of the search circle, which should be non-zero. Default is
1.0.
- max_points:
- Maximum number of data points to use. Do not search for more points than
this number. Found points will be ranked from nearest to furthest distance
when weighting. Default is 12.
- min_points:
- Minimum number of data points to use. If less amount of points found the
grid node is considered empty and will be filled with NODATA marker.
Default is 0.
- nodata:
- NODATA marker to fill empty points (default 0.0).
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 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).
(Since GDAL 2.1) Linear interpolation algorithm.
The Linear method performs linear interpolation by computing a
Delaunay triangulation of the point cloud, finding in which triangle of the
triangulation the point is, and by doing linear interpolation from its
barycentric coordinates within the triangle. If the point is not in any
triangle, depending on the radius, the algorithm will use the value of the
nearest point or the nodata value.
It has following parameters:
- radius:
- In case the point to be interpolated does not fit into a triangle of the
Delaunay triangulation, use that maximum distance to search a nearest
neighbour, or use nodata otherwise. If set to -1, the search distance is
infinite. If set to 0, nodata value will be always used. Default is
-1.
- nodata:
- NODATA marker to fill empty points (default 0.0).
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.
- count:
- A number of data points found in grid node search ellipse.
- average_distance:
- An average distance between the grid node (center of the search ellipse)
and all of the data points found in grid node search ellipse.
- average_distance_pts:
- An average distance between the data points found in grid node search
ellipse. The distance between each pair of points within ellipse is
calculated and average of all distances is set as a grid node value.
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 radii are non-zero). Default is
0.
- nodata:
- NODATA marker to fill empty points (default 0.0).
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.
Starting with GDAL 2.1, this utility is also callable from C with
GDALGrid().
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 previous 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. The GDAL_NUM_THREADS is also set to parallelize
the computation.
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 --config GDAL_NUM_THREADS ALL_CPUS
Andrey Kiselev dron@ak4719.spb.edu