grdproject(1) GMT grdproject(1)
NAME
grdproject - Forward and inverse map transformation of grids
SYNOPSIS
grdproject in_grdfile -Gout_grdfile -Jparameters [ -C[dx/dy] ] [
-Dxinc[unit][+e|n][/yinc[unit][*+e|n]] ] [ -Edpi ] [
-F[c|i|p|e|f|k|M|n|u] ] [ -I ] [ -Mc|i|p ] [ -Rregion ] [ -V[level]
] [ -nflags ] [ -r ]
Note: No space is allowed between the option flag and the associated
arguments.
DESCRIPTION
grdproject will do one of two things depending whether -I has been set.
If set, it will transform a gridded data set from a rectangular coordi-
nate system onto a geographical system by resampling the surface at the
new nodes. If not set, it will project a geographical gridded data set
onto a rectangular grid. To obtain the value at each new node, its
location is inversely projected back onto the input grid after which a
value is interpolated between the surrounding input grid values. By
default bi-cubic interpolation is used. Aliasing is avoided by also
forward projecting the input grid nodes. If two or more nodes are pro-
jected onto the same new node, their average will dominate in the cal-
culation of the new node value. Interpolation and aliasing is con-
trolled with the -n option. The new node spacing may be determined in
one of several ways by specifying the grid spacing, number of nodes, or
resolution. Nodes not constrained by input data are set to NaN.
The -R option can be used to select a map region larger or smaller than
that implied by the extent of the grid file.
REQUIRED ARGUMENTS
in_grdfile
2-D binary grid file to be transformed. (See GRID FILE FORMATS
below.)
-Gout_grdfile
Specify the name of the output grid file. (See GRID FILE FORMATS
below.)
-Jparameters (more a|)
Select map projection.
OPTIONAL ARGUMENTS
-C[dx/dy]
Let projected coordinates be relative to projection center
[Default is relative to lower left corner]. Optionally, add off-
sets in the projected units to be added (or subtracted when -I
is set) to (from) the projected coordinates, such as false east-
ings and northings for particular projection zones [0/0].
-Dxinc[unit][+e|n][/yinc[unit][+e|n]]
Set the grid spacing for the new grid. Append m for arc minute,
s for arc second. If neither -D nor -E are set then we select
the same number of output nodes as there are input nodes.
-Edpi Set the resolution for the new grid in dots per inch.
-F[c|i|p|e|f|k|M|n|u]
Force 1:1 scaling, i.e., output (or input, see -I) data are in
actual projected meters [e]. To specify other units, append f
(foot), k (km), M (statute mile), n (nautical mile), u (US sur-
vey foot), i (inch), c (cm), or p (point). Without -F, the out-
put (or input, see -I) are in the units specified by
PROJ_LENGTH_UNIT (but see -M).
-I Do the Inverse transformation, from rectangular to geographical.
-Mc|i|p
Append c, i, or p to indicate that cm, inch, or point should be
the projected measure unit [Default is set by PROJ_LENGTH_UNIT
in gmt.conf]. Cannot be used with -F.
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
Specify the region of interest. You may ask to project only a
subset of the grid by specifying a smaller input w/e/s/n region
[Default is the region given by the grid file].
-V[level] (more a|)
Select verbosity level [c].
-n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more a|)
Select interpolation mode for grids.
-r (more a|)
Set pixel node registration [gridline].
-^ or just -
Print a short message about the syntax of the command, then
exits (NOTE: on Windows just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion of any module-specific option (but not the GMT common
options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation
of all options, then exits.
GRID FILE FORMATS
By default GMT writes out grid as single precision floats in a
COARDS-complaint netCDF file format. However, GMT is able to produce
grid files in many other commonly used grid file formats and also
facilitates so called apackinga of grids, writing out floating point
data as 1- or 2-byte integers. (more a|)
EXAMPLES
To transform the geographical grid dbdb5.nc onto a pixel Mercator grid
at 300 dpi, run
gmt grdproject dbdb5.nc -R20/50/12/25 -Jm0.25i -E300 -r -Gdbdb5_merc.nc
To inversely transform the file topo_tm.nc back onto a geographical
grid, use
gmt grdproject topo_tm.nc -R-80/-70/20/40 -Jt-75/1:500000 -I -D5m -V -Gtopo.nc
This assumes, of course, that the coordinates in topo_tm.nc were cre-
ated with the same projection parameters.
To inversely transform the file topo_utm.nc (which is in UTM meters)
back to a geographical grid we specify a one-to-one mapping with meter
as the measure unit:
gmt grdproject topo_utm.nc -R203/205/60/65 -Ju5/1:1 -I -Mm -Gtopo.nc -V
To inversely transform the file data.nc (which is in Mercator meters
with Greenwich as the central longitude and a false easting of -4 and
produced on the ellipse WGS-72) back to a geographical grid we specify
a one-to-one mapping with meter as the measure unit:
gmt grdproject data.nc -Jm/1:1 -I -F -C-4/0 -Gdata_geo.nc -V --PROJ_ELLIPSOID=WGS-72
RESTRICTIONS
The boundaries of a projected (rectangular) data set will not necessar-
ily give rectangular geographical boundaries (Mercator is one excep-
tion). In those cases some nodes may be unconstrained (set to NaN). To
get a full grid back, your input grid may have to cover a larger area
than you are interested in.
SEE ALSO
gmt(1), gmt.conf(5), mapproject(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 grdproject(1)
gmt5 5.4.2 - Generated Thu Jun 29 07:42:20 CDT 2017