GRDCONTOUR(1) Generic Mapping Tools GRDCONTOUR(1)NAMEgrdcontour - Contouring of 2-D gridded data sets
SYNOPSISgrdcontour grdfile -Ccont_int -Jparameters [ -A[-|annot_int][labelinfo]
] [ -B[p|s]parameters ] [ -Ddumpfile ] [ -Eazimuth/elevation ] [
-F[l|r] ] [ -G[d|f|n|l|L|x|X]params ] [ -K ] [ -Llow/high ] [ -O ] [ -P
] [ -Qcut ] [ -Rwest/east/south/north[r] ] [ -Ssmoothfactor ] [
-T[+|-][gap/length][:LH] ] [ -U[just/dx/dy/][c|label] ] [ -V ] [
-W[+][type]pen ] [ -X[a|c|r][x-shift[u]] ] [ -Y[a|c|r][y-shift[u]] ] [
-Z[factor[/shift]][p] ] [ -ccopies ] [ -bo[s|S|d|D[ncol]|c[var1/...]] ]
[ -m[flag] ]
DESCRIPTIONgrdcontour reads a 2-D grid 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 out‐
put. Various options that affect the plotting are available.
grdfile
2-D gridded data set to be contoured. (See GRID FILE FORMATS
below).
-C The contours to be drawn may be specified in one of three possi‐
ble ways:
(1) 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
annotation flags in the last column then those contours will be
annotated. By default all contours are labeled; use -A- to dis‐
able all annotations.
(2) 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 annotation
angle for this contour level.
(3) If no file is found, then cont_int is interpreted as a con‐
stant contour interval. If -A is set and -C is not, then the
contour interval is set equal to the specified annotation inter‐
val.
If a file is given and -T is set, then only contours marked with
upper case C or A will have tickmarks. In all cases the contour
values have the same units as the grid.
-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. When central meridian is optional,
default is center of longitude range on -R option. Default
standard parallel is the equator. For map height, max dimen‐
sion, or min dimension, append h, +, or - to the width, respec‐
tively.
More details can be found in the psbasemap man pages.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
-Jj[lon0/]scale (Miller)
-Jm[lon0/[lat0/]]scale (Mercator)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard paral‐
lel)
-Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and
azimuth)
-Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and
pole)
-Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
-Jtlon0/[lat0/]scale (TM - Transverse Mercator)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
-Jpoly/[lon0/[lat0/]]scale ((American) Polyconic)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
-Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
-Jflon0/lat0[/horizon]/scale (Gnomonic)
-Jglon0/lat0[/horizon]/scale (Orthographic)
-Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale
(General Perspective).
-Jslon0/lat0[/horizon]/scale (General Stereographic)
MISCELLANEOUS PROJECTIONS:
-Jh[lon0/]scale (Hammer)
-Ji[lon0/]scale (Sinusoidal)
-Jkf[lon0/]scale (Eckert IV)
-Jk[s][lon0/]scale (Eckert VI)
-Jn[lon0/]scale (Robinson)
-Jr[lon0/]scale (Winkel Tripel)
-Jv[lon0/]scale (Van der Grinten)
-Jw[lon0/]scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
-Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log,
and power scaling)
OPTIONS
No space between the option flag and the associated arguments.
-A annot_int is annotation interval in data units; it is ignored if
contour levels are given in a file. [Default is no annota‐
tions]. Append - to disable all annotations implied by -C.
The optional labelinfo controls the specifics of the label for‐
matting and consists of a concatenated string made up of any of
the following control arguments:
+aangle
For annotations at a fixed angle, +an for line-normal, or
+ap for line-parallel [Default]. By appending the u or d
we get annotations whose top face the next upper or lower
annotation, respectively.
+cdx[/dy]
Sets the clearance between label and optional text box.
Append c|i|m|p to specify the unit or % to indicate a
percentage of the label font size [15%].
+d Turns on debug which will draw helper points and lines to
illustrate the workings of the quoted line setup.
+ffont Sets the desired font [Default ANNOT_FONT_PRIMARY].
+g[color]
Selects opaque text boxes [Default is transparent];
optionally specify the color [Default is PAGE_COLOR].
(See SPECIFYING COLOR below).
+jjust Sets label justification [Default is MC]. Ignored when
-SqN|n+|-1 is used.
+kcolor
Sets color of text labels [Default is COLOR_BACKGROUND].
(See SPECIFYING COLOR below).
+ndx[/dy]
Nudges the placement of labels by the specified amount
(append c|i|m|p to specify the units). Increments are
considered in the coordinate system defined by the orien‐
tation of the line; use +N to force increments in the
plot x/y coordinates system [no nudging].
+o Selects rounded rectangular text box [Default is rectan‐
gular]. Not applicable for curved text (+v) and only
makes sense for opaque text boxes.
+p[pen]
Draws the outline of text boxsets [Default is no out‐
line]; optionally specify pen for outline [Default is
width = 0.25p, color = black, texture = solid]. (See
SPECIFYING PENS below).
+rmin_rad
Will not place labels where the line's radius of curva‐
ture is less than min_rad [Default is 0].
+ssize Sets the desired font size in points [Default is 9].
+uunit Appends unit to all line labels. If unit starts with a
leading hyphen (-) then there will be no space between
label value and the unit. If z is appended we use the
unit specified in the grid file. [Default is no unit].
+v Specifies curved labels following the path [Default is
straight labels].
+w Specifies how many (x, y) points will be used to estimate
label angles [Default is 10].
+=prefix
Prepends prefix to all line labels. If prefix starts
with a leading hyphen (-) then there will be no space
between label value and the prefix. [Default is no pre‐
fix].
-B Sets map boundary annotation and tickmark intervals; see the
psbasemap man page for all the details.
-D Dump the (x,y,z) coordinates of each contour to separate files,
one for each contour segment. The files will be named dump‐
file_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 cre‐
ated instead.
-E Sets the viewpoint's azimuth and elevation (for perspective
view) [180/90]. For frames used for animation, you may want to
append + to fix the center of your data domain (or specify a
particular world coordinate point with +wlon0/lat[/z]) which
will project to the center of your page size (or specify the
coordinates of the projected view point with +vx0/y0).
-F Force dumped contours to be oriented so that higher z-values are
to the left (-Fl [Default]) or right (-Fr) as we move along the
contour [Default is arbitrary orientation]. Requires -D.
-G Controls the placement of labels along the contours. Choose
among five controlling algorithms:
-Gddist[c|i|m|p] or -GDdist[d|e|k|m|n]
For lower case d, give distances between labels on the
plot in your preferred measurement unit c (cm), i (inch),
m (meter), or p (points), while for upper case D, specify
distances in map units and append the unit; choose among
e (m), k (km), m (mile), n (nautical mile), or d (spheri‐
cal degree). [Default is 10c or 4i].
-Gfffile.d
Reads the ascii file ffile.d and places labels at loca‐
tions in the file that matches locations along the con‐
tours. Inexact matches and points outside the region are
skipped.
-Gl|Lline1[,line2,...]
Give the coordinates of the end points for one or more
comma-separated straight line segments. Labels will be
placed where these lines intersect the contours. The for‐
mat of each line specification is
start_lon/start_lat/stop_lon/stop_lat. Both
start_lon/start_lat and stop_lon/stop_lat can be replaced
by a 2-character key that uses the justification format
employed in pstext to indicate a point on the map, given
as [LCR][BMT]. In addition, you may use Z+ and Z- which
correspond to the locations of the global max and min
locations in the grid, respectively. -GL will interpret
the point pairs as defining great circles [Default is
straight line].
-Gn|Nn_label
Specifies the number of equidistant labels for contours
line [1]. Upper case -GN starts labeling exactly at the
start of the line [Default centers them along the line].
-GN-1 places one justified label at start, while -GN+1
places one justified label at the end of contours.
Optionally, append /min_dist[c|i|m|p] to enforce that a
minimum distance separation between successive labels is
enforced.
-Gx|Xxfile.d
Reads the multi-segment file xfile.d and places labels at
the intersections between the contours and the lines inx‐
file.d. -GX will resample the lines first along great-
circle arcs.
In addition, you may optionally append +rradius[c|i|m|p] to set
a minimum label separation in the x-y plane [no limitation].
-K More PostScript code will be appended later [Default terminates
the plot system].
-L Limit range: Do not draw contours for data values below low or
above high.
-O Selects Overlay plot mode [Default initializes a new plot sys‐
tem].
-P Selects Portrait plotting mode [Default is Landscape, see gmtde‐
faults to change this].
-Q Do not draw contours with less than cut number of points [Draw
all contours].
-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 w/e/s/n.
The two shorthands -Rg and -Rd stand for global domain (0/360
and -180/+180 in longitude respectively, with -90/+90 in lati‐
tude). Alternatively, specify the name of an existing grid file
and the -R settings (and grid spacing, if applicable) are copied
from the grid. For calendar time coordinates you may either
give (a) relative time (relative to the selected TIME_EPOCH and
in the selected TIME_UNIT; append t to -JX|x), or (b) 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 delim‐
iters and their type and positions must be exactly as indicated
(however, input, output and plot formats are customizable; see
gmtdefaults). [Default is region defined in the grid file].
-S Used to resample the contour lines at roughly every (grid‐
box_size/smoothfactor) interval.
-T 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 con‐
tours marked with upper case C or A will have tickmarks [and
annotation].
-U Draw Unix System time stamp on plot. By adding just/dx/dy/, the
user may specify the justification of the stamp and where the
stamp should fall on the page relative to lower left corner of
the plot. For example, BL/0/0 will align the lower left corner
of the time stamp with the lower left corner of the plot.
Optionally, append a label, or c (which will plot the command
string.). The GMT parameters UNIX_TIME, UNIX_TIME_POS, and
UNIX_TIME_FORMAT can affect the appearance; see the gmtdefaults
man page for details. The time string will be in the locale set
by the environment variable TZ (generally local time).
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-W type, if present, can be a for annotated contours or c for regu‐
lar contours [Default]. pen sets the attributes for the partic‐
ular line. Default values for annotated contours: width =
0.75p, color = black, texture = solid. Regular contours have
default width = 0.25p. (See SPECIFYING PENS below). If the +
flag is specified then the color of the contour lines are taken
from the cpt file (see -C).
-X -Y Shift plot origin relative to the current origin by (x-shift,y-
shift) and optionally append the length unit (c, i, m, p). You
can prepend a to shift the origin back to the original position
after plotting, or prepend r [Default] to reset the current
origin to the new location. If -O is used then the default (x-
shift,y-shift) is (0,0), otherwise it is (r1i, r1i) or (r2.5c,
r2.5c). Alternatively, give c to align the center coordinate (x
or y) of the plot with the center of the page based on current
page size.
-Z 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 scaling and translation have occurred.)
Append p to indicate that this grid file contains z-values that
are periodic in 360 degrees (e.g., phase data, angular distribu‐
tions) and that special precautions must be taken when determin‐
ing 0-contours.
-bo Selects binary output. Append s for single precision [Default
is d (double)]. Uppercase S or D will force byte-swapping.
Optionally, append ncol, the number of desired columns in your
binary output file.
-c Specifies the number of plot copies. [Default is 1].
-f Special formatting of input and/or output columns (time or geo‐
graphical data). Specify i or o to make this apply only to
input or output [Default applies to both]. Give one or more
columns (or column ranges) separated by commas. Append T (abso‐
lute calendar time), t (relative time in chosen TIME_UNIT since
TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
to each column or column range item. Shorthand -f[i|o]g means
-f[i|o]0x,1y (geographic coordinates).
-m When used in conjunction with -D a single multisegment file is
created, and each contour section is preceded by a header record
whose first column is flag followed by the contour level.
SPECIFYING PENS
pen The attributes of lines and symbol outlines as defined by pen is
a comma delimetered list of width, color and texture, each of
which is optional. width can be indicated as a measure (points,
centimeters, inches) or as faint, thin[ner|nest], thick[er|est],
fat[ter|test], or obese. color specifies a gray shade or color
(see SPECIFYING COLOR below). texture is a combination of
dashes `-' and dots `.'.
SPECIFYING COLOR
color The color of lines, areas and patterns can be specified by a
valid color name; by a gray shade (in the range 0-255); by a
decimal color code (r/g/b, each in range 0-255; h-s-v, ranges
0-360, 0-1, 0-1; or c/m/y/k, each in range 0-1); or by a hexa‐
decimal color code (#rrggbb, as used in HTML). See the gmtcol‐
ors manpage for more information and a full list of color names.
ASCII FORMAT PRECISION
The ASCII output formats of numerical data are controlled by parameters
in your .gmtdefaults4 file. Longitude and latitude are formatted
according to OUTPUT_DEGREE_FORMAT, whereas other values are formatted
according to D_FORMAT. Be aware that the format in effect can lead to
loss of precision in the output, which can lead to various problems
downstream. If you find the output is not written with enough preci‐
sion, consider switching to binary output (-bo if available) or specify
more decimals using the D_FORMAT setting.
FILE FORMATS
GMT is able to recognize many of the commonly used grid file formats,
as well as the precision, scale and offset of the values contained in
the grid file. When GMT needs a little help with that, you can add the
suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of
the grid type and precision, and scale and offset are optional scale
factor and offset to be applied to all grid values, and nan is the
value used to indicate missing data. See grdreformat(1) and Section
4.17 of the GMT Technical Reference and Cookbook for more information.
When reading a netCDF file that contains multiple grids, GMT will read,
by default, the first 2-dimensional grid that can find in that file. To
coax GMT into reading another multi-dimensional variable in the grid
file, append ?varname to the file name, where varname is the name of
the variable. Note that you may need to escape the special meaning of ?
in your shell program by putting a backslash in front of it, or by
placing the filename and suffix between quotes or double quotes. See
grdreformat(1) and Section 4.18 of the GMT Technical Reference and
Cookbook for more information, particularly on how to read splices of
3-, 4-, or 5-dimensional grids.
EXAMPLES
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:
grdcontour hawaii_grav.grd -Jm 0.5i -C 25 -A 50+s10 -B 1g30m >
hawaii_grav.ps
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, and send the output to the default printer:
grdcontour image.grd -Jx 0.1c/50.0c -C cont.d -S 4 -B 20/0.1:."RMS Mis‐
fit": -Wa thick,red -Wc thinnest,blue,- | lp
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.
SEE ALSOGMT(1), gmtdefaults(1), gmtcolors(5), psbasemap(1), grdimage(1), grd‐
view(1), pscontour(1)GMT 4.5.14 1 Nov 2015 GRDCONTOUR(1)
