---
name: "grdsample"
section: "1"
platform: "linux"
package: "gmt-manpages"
version: "3.4-1"
release: "Debian 3.0 (Woody)"
platforms: ["linux"]
url: "https://new.carta.tech/grdsample"
---

# grdsample(1)

Resample a grd file onto a new grid

## NAME

grdsample - Resample a grd file onto a new grid

## SYNOPSIS

**grdsample** *in\_grdfile* **-G***out\_grdfile* \[ **-F** \] \[ **-I***dx*\[**m\|c**\]\[/*dy*\[**m\|c**\]\] \] \[ **-L***flag* \] \[ **-N***nx/ny* \] \[ **-Q** \] \[ **-R***west/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* indicating geographical conditions (x and y are lon and lat). \[Default uses "natural" conditions (second partial derivative normal to edge is zero).\]

- **-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 important. 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 **-I**1**m -G**hawaii\_1by1\_topo.grd\

To translate the gridline-registered file surface.grd to pixel registration, try\

grdsample surface.grd **-T -G**pixel.grd

## SEE ALSO

*gmt*(l), *grdedit*(l), *grdfft*(l), *grdfilter*(l)