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

# grdreformat(1)

Converting between different grdfile formats.

## NAME

grdreformat - Converting between different grdfile formats.

## SYNOPSIS

**grdreformat** *ingrdfile*\[*=id*\[*/scale/offset*\[*/nanvalue*\]\]\] *outgrdfile*\[*=id*\[*/scale/offset*\[*/nanvalue*\]\]\] \[ **-R***west/east/south/north*\[**r**\] \] \[ **-V** \]

## DESCRIPTION

**grdreformat** reads a grdfile in one format and writes it out using another format. As an option the user may select a subset of the data to be written and to specify scaling, translation, and nan-value.

- *ingrdfile*

  The grdfile to be read. Append format =*id* number if not a standard GMT netcdf-based grdfile. If *id* is set, you may optionally append *scale* and *offset* to scale the data and then add an offset. If *scale* and *offset* are supplied you may also append a value that represent 'not-a-number' (for floating-point grids this is unneccesary since the IEEE NaN is used; however short integers need a value which means no data available.)

- *outgrdfile*

  The grdfile to be written. Append format =*id* number if not a standard GMT netcdf-based grdfile. If *id* is set, you may optionally append *scale* and *offset* to scale the data and then add an offset. If *scale* and *offset* are supplied you may also append a value that represent 'not-a-number' (for floating-point grids this is unneccesary since the IEEE NaN is used; however short integers need a value which means no data available.) For format =*id* \> 0 the size of the GMT grdheader block is *hsize* = 896 bytes, and the total size of the file is *hsize + nx \* ny \* item\_size*, where item\_size *is the size in bytes of each element (1, 2, 4). Bit grids* *are stored using 4-byte integers, each holding 32 bits, so for these files the size equation is modified by* *using ceil (nx / 32) \* 4 instead of nx. For header and grid details, see Appendix B.*

## OPTIONS

- **-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 \[Default runs "silently"\].*

## EXAMPLES

*To create a 4-byte raw floating point grid from the netcdf file data.grd, try*\

*grdreformat data.grd ras\_data.b4=1* **-V**\

*To make a 2-byte short integer file, scale it by 10, subtract 32000, setting* *NaNs to -9999, do*\

*grdreformat values.grd shorts.i2=2/10/-32000/-9999* **-V**\

*To create a Sun standard 8-bit rasterfile for a subset of the data file image.grd,* *assuming the range in image.grd is 0-1 and we need 0-255, try*\

*grdreformat image.grd* **-R***-60/-40/-40/-30 image.ras8=3/255/0* **-V**

## SEE ALSO

*gmt*(l), *grdmath*(l)