grdproject - Forward and Inverse map transformation of 2-D grd files

grdprojectin_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]

grdprojectwill do one of two things depending whether-Ihas 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 thesearch_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 NaN. No space between the option flag and the associated arguments. Use upper case for the option flags and lower case for modifiers.in_grdfile2-D binary grd file to be transformed.-JSelects 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 appendingc,i, ormto the scale/width value. For map height, max dimension, or min dimension, appendh,+, or-to the width, respectively.CYLINDRICALPROJECTIONS:-Jclon0/lat0/scale(Cassini)-Jjlon0/scale(Miller)-Jmscale(Mercator - Greenwich and Equator as origin)-Jmlon0/lat0/scale(Mercator - Give meridian and standard paral- lel)-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 Car- ree))-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)AZIMUTHALPROJECTIONS:-Jalon0/lat0/scale(Lambert).-Jelon0/lat0/scale(Equidistant).-Jflon0/lat0/horizon/scale(Gnomonic).-Jglon0/lat0/scale(Orthographic).-Jslon0/lat0/[slat/]scale(General Stereographic)CONICPROJECTIONS:-Jblon0/lat0/lat1/lat2/scale(Albers)-Jdlon0/lat0/lat1/lat2/scale(Equidistant)-Jllon0/lat0/lat1/lat2/scale(Lambert)MISCELLANEOUSPROJECTIONS:-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-GEOGRAPHICALPROJECTIONS:-Jp[a]scale[/origin] (polar (theta,r) coordinates, optionalafor azimuths and offset theta [0])-Jxx-scale[l|ppow][/y-scale[l|ppow]][d] (Linear, log, and power scaling) More details can be found in thepsbasemapman pages.-Rxmin,xmax,ymin,andymaxspecify the Region of interest. For geographic regions, these limits correspond towest,east,south,andnorthand you may specify them in decimal degrees or in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Appendrif lower left and upper right map coordinates are given instead of wesn. The two shorthands-Rg-Rdstand 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; appendtto-JX|x), or absolute time of the form [date]T[clock] (appendTto-JX|x). At least one ofdateandclockmust be present; theTis always required. Thedatestring must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or yyyy[-Www[-d]] (ISO week calendar), while theclockstring 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).

-AForce 1:1 scaling, i.e., output (or input, see-I) data are in actual projected meters. To specify other units, appendk(km),m(mile),n(nautical mile),i(inch),c(cm), orp(points). Without-A, the output (or input, see-I) are in the units spec- ified by MEASURE_UNIT (but see-M).-CLet 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-Iis set) to (from) the projected coordinates, such as false eastings and northings for particular projection zones [0/0].-DSet the grid spacing for the new grid. Appendmfor minutes,cfor seconds.-ESet the resolution for the new grid in dots per inch.-FToggle between pixel and gridline registration [Default is same as input].-GSpecify the name of the output netCDF grd file.-IDo the Inverse transformation, from rectangular to geographical.-MAppendc,i, ormto 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.-NSet the number of grid nodes in the new grid.-SSet the search radius for the averaging procedure [Default avoids aliasing].-VSelects 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, rungrdprojectdbdb5.grd-R20/50/12/25-Jm0.25i-E300-F-Gdbdb5_merc.grd To inversely transform the file topo_tm.grd back onto a geographical grid, usegrdprojecttopo_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 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:grdprojecttopo_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)

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