grdviewgmt - Online in the Cloud

PROGRAM:

NAME

grdview - Create 3-D perspective image or surface mesh from a grid

SYNOPSIS

grdview relief_file parameters [ [p|s]parameters ] [ [cpt]] [ drapefile |
grd_r,grd_g,grd_b ] [ intensfile|intensity ] [ -Jz|Zparameters ] [ -K ] [ level[+gfill] ]
[ -O ] [ -P ] [ args[+m] ] [ west/east/south/north[/zmin/zmax][r] ] [ smooth ] [
[s][o[pen]] ] [ [just/dx/dy/][c|label] ] [ typepen ] [ x_offset ] [ y_offset ] [ -ccopies
] [ -n<flags> ] [ -p<flags> ] [ -t<transp> ]

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

DESCRIPTION

grdview reads a 2-D grid file and produces a 3-D perspective plot by drawing a mesh,
painting a colored/grayshaded surface made up of polygons, or by scanline conversion of
these polygons to a raster image. Options include draping a data set on top of a surface,
plotting of contours on top of the surface, and apply artificial illumination based on
intensities provided in a separate grid file.

REQUIRED ARGUMENTS

relief_file
2-D gridded data set to be imaged (the relief of the surface). (See GRID FILE
FORMAT below.)

-Jparameters (more ...)
Select map projection.

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

OPTIONAL ARGUMENTS

-B[p|s]parameters (more ...)
Set map boundary intervals.

-C[cpt]
name of the CPT file. Must be present if you want (1) mesh plot with contours
(-Qm), or (2) shaded/colored perspective image (-Qs or -Qi). For -Qs: You can
specify that you want to skip a z-slice by setting red = -; to use a pattern give
red = P|pdpi/pattern[:Fcolor[Bcolor]]. Alternatively, supply the name of a GMT
color master CPT [rainbow] and let grdview automatically determine a 16-level
continuous CPT from the grid's z-range.

-Gdrapefile | -Ggrd_r,grd_g,grd_b
Drape the image in drapefile on top of the relief provided by relief_file. [Default
is relief_file]. Note that -Jz and -N always refers to the relief_file. The
drapefile only provides the information pertaining to colors, which is looked-up
via the CPT file (see -C). Alternatively, give three grid files separated by
commas. These files must contain the red, green, and blue colors directly (in 0-255
range) and no CPT file is needed. The drapefile may be of higher resolution than
the relief_file.

-Iintensfile|intensity
Gives the name of a grid file with intensities in the (-1,+1) range, or a constant
intensity to apply everywhere. [Default is no illumination].

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

-Nlevel[+gfill]
Draws a plane at this z-level. If the optional color is provided via the +g
modifier, the frontal facade between the plane and the data perimeter is colored.
See -Wf for setting the pen used for the outline.

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

-P (more ...)
Select "Portrait" plot orientation.

-Qargs[+m]
Select one of following settings. For any of these choices, you may force a
monochrome image by appending the modifier +m. Colors are then converted to shades
of gray using the (monochrome television) YIQ transformation

1. Specify m for mesh plot [Default], and optionally append color for a different
mesh paint [white].

2. Specify mx or my for waterfall plots (row or column profiles). Specify color as
for plain m

3. Specify s for surface plot, and optionally append m to have mesh lines drawn on
top of surface.

4. Specify i for image plot, and optionally append the effective dpi resolution for
the rasterization [100].

5. Specify c. Same as -Qi but will make nodes with z = NaN transparent, using the
colormasking feature in PostScript Level 3 (the PS device must support PS Level
3). .

-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest.

For perspective view p, optionally append /zmin/zmax. (more ...) This option may be used
to indicate the range used for the 3-D axes [Default is region given by the relief_file].
You may ask for a larger w/e/s/n region to have more room between the image and the axes.
A smaller region than specified in the relief_file will result in a subset of the grid.

-Ssmooth
Smooth the contours before plotting (see grdcontour) [Default is no smoothing].

-T[s][o[pen]]
Plot image without any interpolation. This involves converting each node-centered
bin into a polygon which is then painted separately. Append s to skip nodes with z
= NaN. This option is useful for categorical data where interpolating between
values is meaningless. Optionally, append o to draw the tile outlines, and specify
a custom pen if the default pen is not to your liking. As this option produces a
flat surface it cannot be combined with -JZ or -Jz.

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

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

-Wtypepen

-Wc Draw contour lines on top of surface or mesh (not image). Append pen attributes
used for the contours. [Default: width = 0.75p, color = black, style = solid].

-Wm Sets the pen attributes used for the mesh. [Default: width = 0.25p, color =
black, style = solid]. You must also select -Qm or -Qsm for meshlines to be
drawn.

-Wf Sets the pen attributes used for the facade. [Default: width = 0.25p, color =
black, style = solid]. You must also select -N for the facade outline to be
drawn.

-X[a|c|f|r][x-shift[u]]

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

-ccopies (more ...)
Specify number of plot copies [Default is 1].

-n[b|c|l|n][+a][+bBC][+c][+tthreshold] (more ...)
Select interpolation mode for grids.

-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
use just -).

-+ 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 options, then
exits.

--version
Print GMT version and exit.

--show-datadir
Print full path to GMT share directory and exit.

GRID FILE FORMATS

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. To specify the precision, scale and offset, the user should
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. In case
the two characters id is not provided, as in =/scale than a id=nf is assumed. When
reading grids, the format is generally automatically recognized. If not, the same suffix
can be added to input grid file names. See grdconvert and Section grid-file-format 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. The ?varname suffix can also be used
for output grids to specify a variable name different from the default: "z". See
grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical
Reference and Cookbook for more information, particularly on how to read splices of 3-,
4-, or 5-dimensional grids.

CONSEQUENCES OF GRID RESAMPLING

Except for Cartesian cases, we need to resample your geographic grid onto an equidistant
projected grid. In doing so various algorithms come into play that projects data from one
lattice to another while avoiding anti-aliasing, leading to possible distortions. One
expected effect of resampling with splines is the tendency for the new resampled grid to
slightly exceed the global min/max limits of the original grid. If this is coupled with
tight CPT file limits you may find that some map areas may show up with fore- or
background color due to the resampling. In that case you have two options: (1) Modify
your CPT file to fit the resampled extrema (reported with -V) or (2) Impose clipping of
resampled values so they do not exceed the input min/max values (add +c to your -n
option).

EXAMPLES

To make a mesh plot from the file hawaii_grav.nc and drawing the contours given in the CPT
file hawaii.cpt on a Lambert map at 1.5 cm/degree along the standard parallels 18 and 24,
with vertical scale 20 mgal/cm, and looking at the surface from SW at 30 degree elevation,
run

gmt grdview hawaii_grav.nc -Jl18/24/1.5c -Chawaii.cpt \
-Jz0.05c -Qm -N-100 -p225/30 -Wc > hawaii_grav_image.ps

To create a illuminated color perspective plot of the gridded data set image.nc, using the
CPT file color.rgb, with linear scaling at 10 cm/x-unit and tickmarks every 5 units, with
intensities provided by the file intens.nc, and looking from the SE, use

gmt grdview image.nc -Jx10.0c -Ccolor.rgb -Qs -p135/30 -Iintens.nc > image3D.ps

To make the same plot using the rastering option with dpi = 50, use

gmt grdview image.nc -Jx10.0c -Ccolor.rgb -Qi50 -p135/30 -Iintens.nc > image3D.ps

To create a color PostScript perspective plot of the gridded data set magnetics.nc, using
the CPT file mag_intens.cpt, draped over the relief given by the file topography.nc, with
Mercator map width of 6 inch and tickmarks every 1 degree, with intensities provided by
the file topo_intens.nc, and looking from the SE, run

gmt grdview topography.nc -JM6i -Gmagnetics.nc -Cmag_intens.cpt \
-Qs -p140/30 -Itopo_intens.nc > draped3D.ps

Given topo.nc and the Landsat image veggies.ras, first run grd2rgb to get the red, green,
and blue grids, and then drape this image over the topography and shade the result for
good measure. The commands are

gmt grd2rgb veggies.ras -Glayer_%c.nc
gmt grdview topo.nc -JM6i -Qi -p140/30 -Itopo_intens.nc \
-Glayer_r.nc,layer_g.nc,layer_b.nc > image.ps

REMARKS

For the -Qs option: PostScript provides no way of smoothly varying colors within a
polygon, so colors can only vary from polygon to polygon. To obtain smooth images this way
you may resample the grid file(s) using grdsample or use a finer grid size when running
gridding programs like surface or nearneighbor. Unfortunately, this produces huge
PostScript files. The alternative is to use the -Qi option, which computes bilinear or
bicubic continuous color variations within polygons by using scanline conversion to image
the polygons.

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