grdproject - Forward and Inverse map transformation of 2-D grd files
grdproject in_grdfile -Jparameters -Rwest/east/south/north[r] [
-Ddx[m|c][/dy[m|c]] ] [ -Edpi ] [ -F ] [ -Gout_grdfile ] [ -I ] [ -M[m]
] [ -Nnx/ny ] [ -Ssearch_radius ] [ -V ]
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
coordinate 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. The new nodes are filled based on a
simple weighted average of nearby points. Aliasing is avoided by
using sensible values for the search_radius. 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.
No space between the option flag and the associated arguments.
Use upper case for the option flags and lower case for modifiers.
2-D binary grd file to be transformed.
-J Selects the map projection. Scale is inch/degree, 1:xxxxx, or
width in inch (upper case modifier).
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard
-Joalon0/lat0/azimuth/scale (Oblique Mercator - point and
-Joblon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
-Jqlon0/scale (Equidistant Cylindrical Projection (Plate Carree))
-Jtlon0/scale (TM - Transverse Mercator)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)
-Jslon0/lat0/scale (General Stereographic)
-Jklon0/scale (Eckert VI)
-Jrlon0/scale (Winkel Tripel)
-Jpscale (Linear projection for polar (theta,r) coordinates)
-Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and power
More details can be found in the psbasemap manpages.
-R west, east, south, and north specify the Region of interest. To
specify boundaries in degrees and minutes [and seconds], use the
dd:mm[:ss] format. Append r if lower left and upper right map
coordinates are given instead of wesn.
-D Set the grid spacing for the new grid. Append m for minutes, c
-E Set the resolution for the new grid in dots pr inch.
-F Force pixel registration [Default is grid registration].
-G Specify the name of the output netCDF grd file.
-I Do the Inverse transformation, from rectangular to geographical.
-M Let transformed coordinates be relative to projection center
[Default is relative to lower left corner]. Append m to indicate
that meters should be the measure unit [inch].
-N Set the number of grid nodes in the new grid.
-S Set the search radius for the averaging procedure [Default
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
To transform the geographical grid dbdb5.grd onto a pixel Mercator
grid at 300 dpi, run
grdproject dbdb5.grd -R20/50/12/25 -Jm0.25i -E300 -F -Gdbdb5_merc.grd
To inversely transform the file topo_tm.grd back onto a geographical
grdproject topo_tm.grd -R-80/-70/20/40 -Jt-75/1:500000 -I -D5m -V
This assumes, of course, that the coordinates in topo_tm.grd were
created with the same projection parameters.
To inversely transform the file topo_utm.grd (which is in UTM meters)
back onto a geographical grid we specify a one-to-one mapping with
meter as the measure unit:
grdproject topo_utm.grd -R203/05/60/65 -Ju5/1:1 -I -Mm -V -Gtopo.grd
The boundaries of a projected (rectangular) data set will not
necessarily give rectangular geographical boundaries (Mercator is one
exception). 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 interrested in.
gmt, gmtdefaults, mapproject
Man(1) output converted with