NAME
grdproject - Forward and Inverse map transformation of 2-D
grd files
SYNOPSIS
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 ]
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 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 sim-
ple 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.
in_grdfile
2-D binary grd file to be transformed.
-J Selects the map projection. Scale is UNIT/degree,
1:xxxxx, or width in UNIT (upper case modifier). UNIT
is cm, inch, or m, depending on the MEASURE_UNIT set-
ting in .gmtdefaults, but this can be overridden on the
command line by appending the c, i, or m to the
scale/width value.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and stan-
dard parallel)
-Joalon0/lat0/azimuth/scale (Oblique Mercator - point
and azimuth)
-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, with Equator
as y = 0)
-Jtlon0/lat0/scale (TM - Transverse Mercator, set ori-
gin)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0/scale (Lambert).
-Jelon0/lat0/scale (Equidistant).
-Jflon0/lat0/horizon/scale (Gnomonic).
-Jglon0/lat0/scale (Orthographic).
-Jslon0/lat0/scale (General Stereographic)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert)
MISCELLANEOUS PROJECTIONS:
-Jhlon0/scale (Hammer)
-Jilon0/scale (Sinusoidal)
-Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
-Jnlon0/scale (Robinson)
-Jrlon0/scale (Winkel Tripel)
-Jvlon0/scale (Van der Grinten)
-Jwlon0/scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jpscale[/origin] (polar (theta,r) coordinates, option-
ally offset theta [0])
-Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and
power scaling)
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.
OPTIONS
-D Set the grid spacing for the new grid. Append m for
minutes, c for seconds.
-E Set the resolution for the new grid in dots pr inch.
-F Toggle between pixel and gridline registration [Default
is same as input].
-G Specify the name of the output netCDF grd file.
-I Do the Inverse transformation, from rectangular to geo-
graphical.
-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 [Default is set in .gmtdefaults].
-N Set the number of grid nodes in the new grid.
-S Set the search radius for the averaging procedure
[Default avoids aliasing].
-V Selects verbose mode, which will send progress reports
to stderr [Default runs "silently"].
EXAMPLES
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 geo-
graphical grid try
grdproject topo_tm.grd -R-80/-70/20/40 -Jt-75/1:500000 -I
-D5m -V -Gtopo.grd
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
RESTRICTIONS
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.
SEE ALSO
gmt(l), gmtdefaults(l), mapproject(l)