## NAME

          grdcontour - contouring of 2-D gridded data sets

## SYNOPSIS

          grdcontour grdfile -Ccont_int -Jparameters [ -A[-
          ][anot_int][ffont_size][aangle][/r/g/b][o]] ] [ -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] ]

## DESCRIPTION

          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.

          grdfile
               2-D gridded data set to be contoured

          -C   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 no contours are labeled; use -A to anotate all contours.
               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.

          -J   Selects the map projection. Scale is cm/degree, 1:xxxxx, or width
               in cm (upper case modifier).

               CYLINDRICAL PROJECTIONS:

               -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)

               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 (Linear projection for polar (theta,r) coordinates)
               -Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and power
               scaling)
               More details can be found in the psbasemap manpages.

## OPTIONS

          No space between the option flag and the associated arguments.

          -A   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], and append o to draw the outline of the
               surrounding text box [Default is no outline].

          -B   Sets map boundary tickmark intervals. See psbasemap for details.

          -D   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.)
               However, when -M is used in conjunction with -D a single
               multisegment file is created instead.

          -E   Sets the viewpoint's azimuth and elevation for perspective view
               [180/90]

          -G   gap is distance in cm 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].

          -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.

          -M   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.

          -N   Appends unit to all contour labels (assuming -A is set).  If no
               name is specified, the unit given in the grdfile will be used
               [Default is no unit].

          -O   Selects Overlay plot mode [Default initializes a new plot
               system].

          -P   Selects Portrait plotting mode [GMT Default is Landscape, see
               gmtdefaults to change this].

          -Q   Do not draw contours with less than cut number of points [Draw
               all contours].

          -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.  [Default is region
               defined in the grd file].

          -S   Used to resample the contour lines at roughly every
               (gridbox_size/smoothfactor) interval.

          -T   Will draw tickmarks pointing in the downward direction every gap
               along the innermost closed contours.  Append gap and tickmark
               length (in cm) or use defaults [0.5c/0.1c].  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].

          -U   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 in cm [Default is (-2c/-2c)].
               Optionally, append a label, or c (which will plot the command
               string.)

          -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
               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) cm  [Default is
               (a2.5c,a2.5c) for new plots, (0,0) for overlays].  Prepend a for
               absolute coordinates; the default (r) will reset plot origin.

          -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 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.

          -c   Specifies the number of plot copies. [Default is 1]

          -bo  Selects binary output.  Append s for single precision [Default is
               double].

## EXAMPLES

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

          grdcontour hawaii_grav.grd -Jm1.5c -C25 -A50f10 -B1g30m >
          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, try

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

## BUGS

          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.
          There are too many options.

## SEE ALSO

          gmt, psbasemap, grdimage, grdview, pscontour