grdcontour(1) contouring of 2-D gridded data sets


grdcontour grdfile -Ccont_int -Jparameters [ -A[-][anot_int][ffont_size][aangle][/r/g/b][o|t]] ] [ -Btickinfo ] [ -Ddumpfile ] [ -Eazimuth/elevation ] [ -Ggap/width ] [ -K ] [ -Llow/high ] [ -M[flag] ] [ -N[[-]unit] ] [ -O ] [ -P ] [ -Qcut ] [ -Rwest/east/south/north[r] ] [ -Ssmoothfactor ] [ -T[+|-][gap/length][:LH] ] [ -U[/dx/dy/][label] ] [ -V ] [ -W[+][type]pen ] [ -Xx-shift ] [ -Yy-shift ] [ -Z[factor[/shift]][p] ] [ -ccopies ] [ -bo[s[n]] ]


grdcontour reads a 2-D gridded file and produces a contour map by tracing each contour through the grid. As an option, the x/y/z positions of the contour lines may be dumped to a single multisegment file or many separate files. PostScript code is generated and sent to standard output. Various options that affect the plotting are available.

        No space between the option flag and the associated arguments. Use upper case for the option flags and lower case for modifiers.
2-D gridded data set to be contoured
The contours to be drawn may be specified in one of three possible ways:
If cont_int has the suffix ".cpt" and can be opened as a file, it is assumed to be a color palette table. The color boundaries are then used as contour levels. If the cpt-file has anotation flags in the last column then those contours will be anotated. By default all contours are labeled; use -A- to disable all anotations.
If cont_int is a file but not a cpt-file, it is expected to contain contour levels in column 1 and a C(ontour) OR A(nnotate) in col 2. The levels marked C (or c) are contoured, the levels marked A (or a) are contoured and annotated. Optionally, a third column may be present and contain the fixed anotation angle for this contour level.
If no file is found, then cont_int is interpreted as a constant contour interval. If -A is set and -C is not, then the contour interval is set equal to the specified anotation interval.
If a file is given and -T is set, then only contours marked with upper case C or A will have tickmarks.
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 .gmtdefaults, but this can be overridden on the command line by appending the c, i, or m to the scale/width value.


-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard 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 origin)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)


-Jalon0/lat0/scale (Lambert).
-Jelon0/lat0/scale (Equidistant).
-Jflon0/lat0/horizon/scale (Gnomonic).
-Jglon0/lat0/scale (Orthographic).
-Jslon0/lat0/[slat/]scale (General Stereographic)


-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert)


-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)


-Jp[a]scale[/origin] (polar (theta,r) coordinates, optional a for azimuths and 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.


No space between the option flag and the associated arguments.
anot_int is annotation interval in data units. Ignored if contour levels are given in a file. [Default is no annotations]. Several options can be set to modify the form of the annotation. Give - to disable all anotations. Append ffont_size to change font size [9], append /r/g/b to change color of text fill box [PAGE_COLOR], append aangle to fix annotation angle [Default follows contour], append o to draw the outline of the surrounding text box [Default is no outline], or append t to use a transparent label box [Default is opaque].
Sets map boundary tickmark intervals. See psbasemap for details.
Dump the (x,y,z) coordinates of each contour to separate files, one for each contour segment. The files will be named dumpfile_cont_segment[_i].xyz (or .b is -b is selected), where cont is the contour value and segment is a running segment number for each contour interval (for closed contours we append _i.) If the prefix is given as '-' the file names are instead C#_i (interior) or C#_e (external) plus extension, and # is just a running number. This allows us to make short file names that will work with GNU utilities under DOS. However, when -M is used in conjunction with -D a single multisegment file is created instead.
Sets the viewpoint's azimuth and elevation for perspective view [180/90]'
gap is distance between each annotation along the same contour. width is number of points over which to estimate the best fitting slope for contour labels [Default is 10c/10 or 4i/10].
More PostScript code will be appended later [Default terminates the plot system].
Limit range: Do not draw contours for data values below low or above high.
When used in conjunction with -D a single multisegment file is created, and each contour section is preceeded by a header record whose first column is flag followed by the contour level.
Appends unit to all contour labels (assuming -A is set). If no name is specified, the unit given in the grdfile will be used. If unit starts with a leading - then there will be no space between contour value and the unit. [Default is no unit].
Selects binary output. Append s for single precision [Default is double].
Selects Portrait plotting mode [GMT Default is Landscape, see gmtdefaults to change this].
Do not draw contours with less than cut number of points [Draw all contours].
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. [Default is region defined in the grd file].
Used to resample the contour lines at roughly every (gridbox_size/smoothfactor) interval.
Will draw tickmarks pointing in the downward direction every gap along the innermost closed contours. Append gap and tickmark length or use defaults [0.5c/0.1c or 0.2i/0.04i]. User may choose to tick only local highs or local lows by specifying -T+ or -T-, respectively. Appending :LH will plot the characters L and H at the center of closed innermost contours (local lows and highs). L and H can be any single character (e.g., LH, -+, etc.) If a file is given by -C and -T is set, then only contours marked with upper case C or A will have tickmarks [and anotation].
Draw Unix System time stamp on plot. User may specify where the lower left corner of the stamp should fall on the page relative to lower left corner of plot. Optionally, append a label, or c (which will plot the command string.). The GMT parameters UNIX_TIME and UNIX_TIME_POS can affect the appearance; see the gmtdefaults man page for details.
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"].
type, if present, can be 'a' for annotated contours or 'c' for regular contours [Default]. pen sets the attributes for the particular line. Default values for annotated contours: width = 3, color = black, texture = solid. Regular contours have default width = 1. If the + flag is specified then the color of the contour lines are taken from the cpt file (see -C).
-X -Y
Shift origin of plot by (x-shift,y-shift). Prepend a for absolute coordinates; the default (r) will reset plot origin.
Use to subtract shift from the data and multiply the results by factor before contouring starts [1/0]. (Numbers in A, -C, -L refer to values after this scaling has occurred.) Append p to indicate that this grid file contains z-values that are periodic in 360 degrees (e.g., phase data, angular distributions) and that special precautions must be taken when determining 0-contours.
Specifies the number of plot copies. [Default is 1]
Selects binary output. Append s for single precision [Default is double].


To contour the file hawaii_grav.grd every 25 mGal on a Mercator map at 0.5 inch/degree, annotate every 50 mGal (using fontsize = 10), using 1 degree tickmarks, and draw 30 minute gridlines, try

grdcontour hawaii_grav.grd -Jm0.5i -C25 -A50f10 -B1g30m >

To contour the file image.grd using the levels in the file cont.d on a linear projection at 0.1 cm/x-unit and 50 cm/y-unit, using 20 (x) and 0.1 (y) tickmarks, smooth the contours a bit, use "RMS Misfit" as plot-title, use a thick red pen for annotated contours, and a thin, dashed, blue pen for the rest, try

grdcontour image.grd -Jx0.1c/50.0c -Ccont.d -S4 -B20/0.1:."RMS Misfit": -Wa5/255/0/0 -Wc1/0/0/255ta | lp


The text-outline box has not been implemented for perspective view plots. Anotations will plot correctly, but contours will go right through the text.
The labeling of local highs and lows may plot outside the innermost contour since only the mean value of the contour coordinates is used to position the label.
The size of the white box beneath contour anotations is augmented by dx and dy which are set to 50% and 5% of ANOT_OFFSET, respectively. You must thus change this value in .gmtdefaults to affect the box size.
There are too many options.