grdvolume(1) [debian man page]
GRDVOLUME(l) GRDVOLUME(l) NAME
grdvolume - Calculating volume under a surface within a contour SYNOPSIS
grdvolume grdfile [ -Ccval or -Clow/high/delta ] [ -Lbase ] [ -Rwest/east/south/north[r] ] [ -S[k] ] [ -T ] [ -V[l] ] [ -Zfact[/delta] ] DESCRIPTION
grdvolume reads a 2-D binary grd file and calculates the volume contained between the surface and the plane specified by the given contour (or zero if not given). Alternatively, specify a range of contours to be tried and grdvolume will determine the volume and area inside the contour for all contour values. The contour that produced the maximum mean height (volume/area) is reported as well. This feature may be used with grdfilter in designing an Optimal Robust Separator [Wessel, 1998]. grdfile The name of the input 2-D binary grd file. OPTIONS
No space between the option flag and the associated arguments. -C find area and volume inside the cval contour. Alternatively, search using all contours from low to high in steps of delta. [Default returns entire area and volume of grid]. The area is measured in the plane of the countour. -L Also add in the volume from the level of the contour down to base [Default base is contour]. -S Convert degrees to meters, append k for km [Default is Cartesian]. -T Use curvature minimum rather than maximum height to find best contour value (when contour search is selected with -C). -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. -V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. Append l to see all the results for each contour level tested (when contour search has been selected). -Z Optionally subtract shift before scaling data by fact. [Default is no scaling]. (Numbers in -C, -L refer to values after this scal- ing has occurred). EXAMPLES
To determine the volume in km^3 under the surface hawaii_topo.grd (height in km), try grdvolume hawaii_topo.grd -Sk To find the volume between the surface peaks.grd and the contour z = 250, use grdvolume peaks.grd -Sk -C250 To search for the contour, between 100 and 300 in steps of 10, that maximizes the ratio of volume to surface area for the file peaks.grd, use grdvolume peaks.grd -Sk -C100/300/10 > results.d To see the areas and volumes for all the countours in the previous example, try grdvolume peaks.grd -Sk -Vl -C100/300/10 > results.d SEE ALSO
gmt(1gmt), grdfilter(1gmt) REFERENCES
Wessel, P., 1998, An empirical method for optimal robust regional-residual separation of geophysical data, Math. Geol., 30(4), 391-408. 1 Jan 2004 GRDVOLUME(l)
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GRDSAMPLE(l) GRDSAMPLE(l) NAME
grdsample - Resample a grd file onto a new grid SYNOPSIS
grdsample in_grdfile -Gout_grdfile [ -F ] [ -Idx[m|c][/dy[m|c]] ] [ -Lflag ] [ -Nnx/ny ] [ -Q ] [ -Rwest/east/south/north[r] ] [ -T ] [ -V ] DESCRIPTION
grdsample reads a grdfile and interpolates it to create a new grdfile with either: a different registration (-T); or, a new grid-spacing (-I) or number of nodes (-N), and perhaps also a new sub-region (-R). Interpolation is bicubic [Default] or bilinear (-Q) and uses boundary conditions (-L). Note that using (-R) only is equivalent to grdcut or grdedit -S. grdsample safely creates a fine mesh from a coarse one; the converse may suffer aliasing unless the data are filtered using grdfft or grdfilter. in_grdfile The name of the input 2-D binary grd file. -G The name of the output grd file. OPTIONS
No space between the option flag and the associated arguments. -F Force pixel registration. [Default is grid registration]. -I x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c to indicate seconds. -L Boundary condition flag may be x or y or xy indicating data is periodic in range of x or y or both set by -R, or flag may be g indi- cating geographical conditions (x and y are lon and lat). [Default uses "natural" conditions (second partial derivative normal to edge is zero).] -N Specify number of columns nx and rows ny of new grid. -Q Quick mode, use bilinear rather than bicubic interpolation. -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. -T Translate between grid and pixel registration while keeping -R and -I the same; if input is grid-registered, output will be pixel- registered and vice-versa. The input file determines -R, -I and -N so no other options are necessary (except possibly -L or -Q). -V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. HINTS
If an interpolation point is not on a node of the input grid, then a NaN at any node in the neighborhood surrounding the point will yield an interpolated NaN. Bicubic interpolation [default] yields continuous first derivatives but requires a neighborhood of 4 nodes by 4 nodes. Bilinear interpolation [-Q] uses only a 2 by 2 neighborhood, but yields only zeroth-order continuity. Use bicubic when smoothness is impor- tant. Use bilinear to minimize the propagation of NaNs. EXAMPLES
To resample the 5 x 5 minute grid in hawaii_5by5_topo.grd onto a 1 minute grid, try grdsample hawaii_5by5_topo.grd -I1m -Ghawaii_1by1_topo.grd To translate the gridline-registered file surface.grd to pixel registration, try grdsample surface.grd -T -Gpixel.grd SEE ALSO
gmt(1gmt), grdedit(1gmt), grdfft(1gmt), grdfilter(1gmt) 1 Jan 2004 GRDSAMPLE(l)