grdproject - Forward and Inverse map transformation of 2-D grd files
grdproject in_grdfile -Jparameters -Rwest/east/south/north[r] [
-A[k|m|n|i|c|p] ] [ -C[dx/dy] ] [ -Ddx[m|c][/dy[m|c]] ] [ -Edpi ] [ -F
] [ -Gout_grdfile ] [ -I ] [ -Mc|i|m|p ] [ -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 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. The new nodes are filled based on a simple
weighted average of nearby points. Aliasing is avoided by using sensi-
ble values for the search_radius. The new node spacing may be deter-
mined in one of several ways by specifying the grid spacing, number of
nodes, or resolution. Nodes not constrained by input data are set to
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 UNIT/degree, 1:xxxxx, or
width in UNIT (upper case modifier). UNIT is cm, inch, or m,
depending on the MEASURE_UNIT setting in .gmtdefaults4, but this
can be overridden on the command line by appending c, i, or m to
the scale/width value. For map height, max dimension, or min
dimension, append h, +, or - to the width, respectively.
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard paral-
-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
-Jqlon0/scale (Equidistant Cylindrical Projection (Plate Car-
-Jtlon0/scale (TM - Transverse Mercator, with Equator as y = 0)
-Jtlon0/lat0/scale (TM - Transverse Mercator, set origin)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)
-Jslon0/lat0/[slat/]scale (General Stereographic)
-Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
-Jrlon0/scale (Winkel Tripel)
-Jvlon0/scale (Van der Grinten)
-Jp[a]scale[/origin] (polar (theta,r) coordinates, optional a
for azimuths and offset theta )
-Jxx-scale[l|ppow][/y-scale[l|ppow]][d] (Linear, log, and power
More details can be found in the psbasemap man pages.
-R xmin, xmax, ymin, and ymax specify the Region of interest. For
geographic regions, these limits correspond to west, east,
south, and north and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
and upper right map coordinates are given instead of wesn. The
two shorthands -Rg -Rd stand for global domain (0/360 or
-180/+180 in longitude respectively, with -90/+90 in latitude).
For calendar time coordinates you may either give relative time
(relative to the selected TIME_EPOCH and in the selected
TIME_UNIT; append t to -JX|x), or absolute time of the form
[date]T[clock] (append T to -JX|x). At least one of date and
clock must be present; the T is always required. The date string
must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
yyyy[-Www[-d]] (ISO week calendar), while the clock string must
be of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be as indicated (however, input/output
and plotting formats are flexible).
-A Force 1:1 scaling, i.e., output (or input, see -I) data are in
actual projected meters. To specify other units, append k (km),
m (mile),n (nautical mile), i (inch), c (cm), or p (points).
Without -A, the output (or input, see -I) are in the units spec-
ified by MEASURE_UNIT (but see -M).
-C Let projected coordinates be relative to projection center
[Default is relative to lower left corner]. Optionally, add
offsets in the projected units to be added (or subtracted when
-I is set) to (from) the projected coordinates, such as false
eastings and northings for particular projection zones [0/0].
-D Set the grid spacing for the new grid. Append m for minutes, c
-E Set the resolution for the new grid in dots per inch.
-F Toggle between pixel and gridline registration [Default is same
-G Specify the name of the output netCDF grd file.
-I Do the Inverse transformation, from rectangular to geographical.
-M Append c, i, or m to indicate that cm, inch, or meter should be
the projected measure unit [Default is set by MEASURE_UNIT in
.gmtdefaults4]. Cannot be used with -A.
-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 cre-
ated with the same projection parameters.
To inversely transform the file topo_utm.grd (which is in UTM meters)
back to a geographical grid we specify a one-to-one mapping with meter
as the measure unit:
grdproject topo_utm.grd -R203/205/60/65 -Ju5/1:1 -I -Mm -V -Gtopo.grd
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 interrested in.
gmt(l), gmtdefaults(l), mapproject(l)
GMT4.0 1 Oct 2004 GRDPROJECT(l)
Man(1) output converted with