4.4 Perspective views

Our final undertaking in this tutorial is to examine three-dimensional perspective views. GMT is currently limited to vantage points at infinity; thus we are unable to do fly-by's through canyons etc. The GMT module that produces perspective views of gridded data files is grdview. It can make two kinds of plots:

1. Mesh or wire-frame plot (with or without superimposed contours)

2. Color-coded surface (with optional shading, contours, or draping).

Regardless of plot type, some arguments must be specified; these are

1. relief_file; a gridded data set of the surface.

2. -J for the desired map projection.

3. -JZheight for the vertical scaling.

4. -Eazimuth/elevation for vantage point.

In addition, some options may be required:

Table 4.5: The most useful options in grdview.

Option	Purpose
-Ccptfile	The cptfile is required for color -coded surfaces and for contoured mesh plots
-Gdrape_file	Assign colors using drape_file instead of relief_file
-Iintens_file	File with illumination intensities
-Qm	Selects mesh plot
-Qs[m]	Surface plot using polygons; append m to show mesh. This option allows for -W
-Qidpi[g]	Image by scan-line conversion. Specify dpi; append g to force gray-shade image. -B is disabled.
-Wpen	Draw contours on top of surface (except with -Qi)