Provided by: gmt-common_5.4.3+dfsg-1_all bug


       grdcontour - Make contour map using a grid


       grdcontour grid  -C[+]cont_int|cpt
        -Jparameters  [  -A[-|[+]annot_int][labelinfo] ] [  -B[p|s]parameters ] [  -Dtemplate ] [
       -F[l|r] ] [  -G[d|f|n|l|L|x|X]params ] [  -Jz|Zparameters ] [  -K ] [  -Llow/high ] [   -O
       ]  [   -P  ] [  -Qcut ] [  -Rwest/east/south/north[/zmin/zmax][+r] ] [  -Ssmoothfactor ] [
       -T[+|-][+dgap[/length]][+l[labels]] ]  [   -U[stamp]  ]  [   -V[level]  ]  [   -W[type]pen
       ][+c[l|f]]  [  -Xx_offset ] [  -Yy_offset ] [  -Z[+sfactor][+oshift][+p] ] [ -bobinary ] [
       -donodata ] [ -eregexp ] [ -fflags ] [ -ho[n] ] [ -pflags ] [ -ttransp ]

       Note: No space is allowed between the option flag and the associated arguments.


       grdcontour reads a 2-D grid file and produces  a  contour  map  by  tracing  each  contour
       through  the  grid.  PostScript  code  is  generated  and sent to standard output. Various
       options that affect the plotting are available. Alternatively, the x/y/z positions of  the
       contour  lines  may  be  saved  to  one  or  more  output files (or stdout) and no plot is


       grid   2-D gridded data set to be contoured. (See GRID FILE FORMATS below).

              The contours to be drawn may be specified in one of three possible ways:

              1. If cont_int has the suffix “.cpt” and can be opened as a file, it is assumed  to
                 be  a  CPT. The color boundaries are then used as contour levels. If the CPT has
                 annotation flags in the last column then those contours will  be  annotated.  By
                 default all contours are labeled; use -A- to disable all annotations.

              2. If cont_int is a file but not a CPT, 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 constant contour
                 interval. However, if prepended with the + sign the cont_int is taken as meaning
                 draw  that single contour. The -A option offers the same possibility so they may
                 be used  together  to  plot  a  single  annotated  contour  and  another  single
                 non-annotated  contour,  as in ‘… -A+10 -C+5’ that plots an annotated 10 contour
                 and an non-annotated 5 contour.  If -A is set and -C is not,  then  the  contour
                 interval is set equal to the specified annotation interval.

              If  a file is given and -T is set, then only contours marked with upper case C or A
              will have tick-marks. In all cases the contour values have the same  units  as  the

       -Jparameters (more …)
              Select map projection.


              annot_int is annotation interval in data units; it is ignored if contour levels are
              given in a file. [Default is no annotations]. Append - to disable  all  annotations
              implied by -C. Alternatively prepend + to the annotation interval to plot that as a
              single contour.  The  optional  labelinfo  controls  the  specifics  of  the  label
              formatting  and  consists  of a concatenated string made up of any of the following
              control arguments:

                 For  annotations  at  a  fixed  angle,  +an  for  contour-normal,  or  +ap   for
                 contour-parallel  [Default].   For  +ap, you may optionally append u for up-hill
                 and d for down-hill cartographic annotations.

                 Sets the clearance between label and optional text box. Append c|i|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 contour line setup.

          +e     Delay the plotting of the text. This is used to build a clip path based  on  the
                 text,  then  lay  down  other  overlays  while that clip path is in effect, then
                 turning of clipping with psclip -Cs which finally plots the original text.

          +ffont Sets the desired font [Default FONT_ANNOT_PRIMARY with its size changed to 9p].

                 Selects opaque text boxes [Default is transparent]; optionally specify the color
                 [Default is PS_PAGE_COLOR].

          +jjust Sets label justification [Default is MC].

                 Nudges  the placement of labels by the specified amount (append c|i|p to specify
                 the units). Increments are considered in the coordinate system  defined  by  the
                 orientation  of  the  contour;  use  +N  to  force  increments  in  the plot x/y
                 coordinates system [no nudging]. Not allowed with +v.

          +o     Selects rounded rectangular text box [Default is rectangular].   Not  applicable
                 for curved text (+v) and only makes sense for opaque text boxes.

                 Draws  the outline of text boxes [Default is no outline]; optionally specify pen
                 for outline [Default is width = 0.25p, color = black, style = solid].

                 Will not place labels where the contours’s radius  of  curvature  is  less  than
                 min_rad [Default is 0].

                 Saves contour label x, y, angle, and text to file [Contour_labels.txt].

          +uunit Appends  unit  to all contour labels. [Default is no unit].  If z is appended we
                 use the z-unit from the grdfile.

          +v     Specifies curved labels following the contour [Default is straight labels].

          +w     Specifies  how  many  (x,y)  points  will  be  used  to  estimate  label  angles

                 Prepends prefix to all contour labels. [Default is no prefix].

       -B[p|s]parameters (more …)
              Set map boundary frame and axes attributes.

              Dump  contours  as  data  line  segments; no plotting takes place.  Append filename
              template which may contain C-format specifiers.  If no filename template  is  given
              we  write  all  lines  to  stdout.  If filename has no specifiers then we write all
              lines to a single file.  If a float format (e.g., %6.2f) is found we substitute the
              contour  z-value.   If  an  integer  format  (e.g.,  %06d) is found we substitute a
              running segment count.  If an char format (%c) is found we substitute C  or  O  for
              closed  and  open  contours.   The 1-3 specifiers may be combined and appear in any
              order to produce the the desired number of output files (e.g., just  %c  gives  two
              files,  just  %f  would.  separate segments into one file per contour level, and %d
              would write all segments.  to individual files; see manual page for more examples.

              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.

          The required argument controls the placement of labels along the quoted  lines.  Choose
          among five controlling algorithms:

          ddist[c|i|p] or Ddist[d|e|f|k|m|M|n|s]
                 For  lower  case  d, give distances between labels on the plot in your preferred
                 measurement unit c (cm), i (inch), or  p  (points),  while  for  upper  case  D,
                 specify  distances  in  map  units  and  append  the unit; choose among e (m), f
                 (foot), k (km), M (mile), n (nautical mile) or u (US survey foot),  and  d  (arc
                 degree),  m  (arc  minute),  or  s  (arc  second). [Default is 10c or 4i]. As an
                 option, you can append /fraction which is used to place the very first label for
                 each  contour  when the cumulative along-contour distance equals fraction * dist

                 Reads the ASCII file ffile.d and places labels at locations  in  the  file  that
                 matches locations along the quoted lines. Inexact matches and points outside the
                 region are skipped.

                 Give start and stop coordinates for one or more  comma-separated  straight  line
                 segments.  Labels  will  be placed where these lines intersect the quoted lines.
                 The format of each line specification is start/stop, where start  and  stop  are
                 either  a  specified  point  lon/lat  or  a  2-character  XY  key  that uses the
                 justification format employed in pstext to indicate a point on the map, given as
                 [LCR][BMT].   In  addition,  you  can  use Z-, Z+ to mean the global minimum and
                 maximum locations in the grid. L will interpret  the  point  pairs  as  defining
                 great circles [Default is straight line].

                 Specifies the number of equidistant labels for quoted lines line [1]. Upper case
                 N starts labeling exactly at the start of the line [Default centers  them  along
                 the  line].  N-1  places  one  justified  label  at  start, while N+1 places one
                 justified label at the end of quoted lines. Optionally, append  /min_dist[c|i|p]
                 to  enforce  that  a  minimum  distance  separation between successive labels is

                 Reads the multisegment file xfile.d  and  places  labels  at  the  intersections
                 between  the  quoted  lines  and the lines in xfile.d. X will resample the lines
                 first along great-circle arcs.

          In addition,  you  may  optionally  append  +rradius[c|i|p]  to  set  a  minimum  label
          separation in the x-y plane [no limitation].

       -Jz|Zparameters (more …)
              Set z-axis scaling; same syntax as -Jx.

       -K (more …)
              Do not finalize the PostScript plot.

              Limit range: Do not draw contours for data values below low or above high.

       -O (more …)
              Append to existing PostScript plot.

       -P (more …)
              Select “Portrait” plot orientation.

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

       -Rxmin/xmax/ymin/ymax[+r][+uunit] (more …)
              Specify the region of interest.

       For  perspective view p, optionally append /zmin/zmax. (more …) [Default is region defined
       in the grid file].

              Used to resample the contour lines  at  roughly  every  (gridbox_size/smoothfactor)

              Will  draw  tick  marks  pointing  in  the  downward  direction every gap along the
              innermost closed contours. Append +dgap and optionally  tick  mark  length  (append
              units  as  c, i, or p) or use defaults [15p/3p]. User may choose to tick only local
              highs or local lows by specifying -T+ or  -T-,  respectively.  Append  +llabels  to
              annotate the centers of closed innermost contours (i.e., the local lows and highs).
              If no labels is appended we use - and  +  as  the  labels.  Appending  exactly  two
              characters, e.g., +lLH, will plot the two characters (here, L and H) as labels. For
              more elaborate labels, separate the low and hight label strings with a comma (e.g.,
              +llo,hi).  If  a  file is given by -C and -T is set, then only contours marked with
              upper case C or A will have tick marks [and annotations].

       -U[[just]/dx/dy/][c|label] (more …)
              Draw GMT time stamp logo on plot.

       -V[level] (more …)
              Select verbosity level [c].

       -W[type]pen[+c[l|f]] (more …)
              type, if present, can be a  for  annotated  contours  or  c  for  regular  contours
              [Default].  The  pen  sets  the attributes for the particular line. Default pen for
              annotated contours: 0.75p,black.  Regular contours  use  pen  0.25p,black.  If  the
              modifier +cl is appended then the color of the contour lines are taken from the CPT
              (see -C). If instead modifier +cf is appended then the color from the cpt  file  is
              applied to the contour annotations.  Use just +c for both effects.


       -Y[a|c|f|r][y-shift[u]] (more …)
              Shift 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.

       -bo[ncols][type] (more …)
              Select native binary output.

       -donodata (more …)
              Replace output columns that equal NaN with nodata.

       -f[i|o]colinfo (more …)
              Specify data types of input and/or output columns.

       -h[i|o][n][+c][+d][+rremark][+rtitle] (more …)
              Skip or produce header record(s).

       -p[x|y|z]azim[/elev[/zlevel]][+wlon0/lat0[/z0]][+vx0/y0] (more …)
              Select perspective view.

       -t[transp] (more …)
              Set PDF transparency level in percent.

       -^ or just -
              Print a short message about the syntax of the command, then exits (NOTE: on Windows
              just use -).

       -+ or just +
              Print  an  extensive  usage  (help)  message,  including  the  explanation  of  any
              module-specific option (but not the GMT common options), then exits.

       -? or no arguments
              Print  a  complete  usage (help) message, including the explanation of all options,
              then exits.


       The ASCII output formats of numerical data are controlled by parameters in  your  gmt.conf
       file.  Longitude  and latitude are formatted according to FORMAT_GEO_OUT, absolute time is
       under the control of FORMAT_DATE_OUT and FORMAT_CLOCK_OUT, whereas general floating  point
       values are formatted according to FORMAT_FLOAT_OUT. Be aware that the format in effect can
       lead to loss of precision in ASCII output, which can lead to various problems  downstream.
       If  you find the output is not written with enough precision, consider switching to binary
       output (-bo if available) or specify more decimals using the FORMAT_FLOAT_OUT setting.


       By default GMT writes out grid as single precision floats  in  a  COARDS-complaint  netCDF
       file  format.  However, GMT is able to produce grid files in many other commonly used grid
       file formats and also facilitates so called “packing” of grids, writing out floating point
       data as 1- or 2-byte integers. (more …)


       The  angle of a contour is computed as an average over n points along the contour.  If you
       obtain poor angles you can play with two variables: Change n via the +w  modifier  to  -A,
       and/or  resample  the contour via -S.  For a fixed n the -S will localize the calculation,
       while the opposite is true if you increase n for a constant -S.


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

              gmt grdcontour -Jm0.5i -C25 -A50+f10p -B1g30m >

       To contour the file 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:

              gmt grdcontour -Jx0.1c/50.0c -Ccont.d -S4 -Bx20 -By0.1 \
                         -B+t"RMS Misfit" -Wathick,red -Wcthinnest,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.

       To save  the  smoothed  100-m  contour  lines  in  and  separate  them  into  two
       multisegment files: contours_C.txt for closed and contours_O.txt for open contours, try

              gmt grdcontour -C100 -S4 -Dcontours_%c.txt


       gmt, gmt.conf, gmtcolors, psbasemap, grdimage, grdview, pscontour


       2018, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe