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# grdview

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

## Synopsis

grdview relief_file -Jparameters [ -B[p|s]parameters ] [ -C[cptfile]] [ -Gdrapefile | -Ggrd_r,grd_g,grd_b ] [ -Iintensfile|intensity ] [ -Jz|Zparameters ] [ -K ] [ -Nlevel[+gfill] ] [ -O ] [ -P ] [ -Qargs[+m] ] [ -Rwest/east/south/north[/zmin/zmax][r] ] [ -Ssmooth ] [ -T[s][o[pen]] ] [ -U[just/dx/dy/][c|label] ] [ -Wtypepen ] [ -X[a|c|f|r][x-shift[u]] ] [ -Y[a|c|f|r][y-shift[u]] ] [ -ccopies ] [ -n[b|c|l|n][+a][+bBC][+tthreshold] ] [ -p[x|y|z]azim/elev[/zlevel][+wlon0/lat0[/z0]][+vx0/y0] ] [ -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[cptfile]
  name of the color palette 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 four settings: 1. Specify m for mesh plot [Default], and optionally append color for a different mesh paint [white]. 2. Specify s for surface plot, and optionally append m to have mesh lines drawn on top of surface. 3. Specify i for image plot, and optionally append the effective dpi resolution for the rasterization [100]. 4. 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). 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.

-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.

-^
  Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
+
  Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exits.
-?
  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. When reading grids, the format is generally automatically recognized. If not, the same suffix can be added to input grid file names. See grdreformat and Section Grid file format specifications 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 grdreformat and Section Grid file format specifications 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 color palette 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 color palette 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 color palette 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.

## See Also

gmt, grd2rgb, gmtcolors, grdcontour, grdimage, nearneighbor, psbasemap, pscontour, pstext, surface

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