Except in the situation above when a gridded file is available, we must convert our data to the right format readable by GMT before we can make contour plots and color-coded images. We distinguish between two scenarios:
The former situation may require a simple reformatting (using xyz2grd ), while the latter must be interpolated onto a regular lattice; this process is known as gridding. GMT supports three different approaches to gridding; here, we will briefly discuss the two most common techniques.
All GMT gridding programs have in common the requirement that the
user must specify the grid domain and output filename:
| -–R xmin/ xmax/ ymin/ ymax | The desired grid extent |
| -–I xinc[ m| c][/ yinc[ m| c]] | The grid spacing (append m or c for minutes or seconds of arc) |
| -–G gridfile | The output grid filename |