GMT 添加指南针
有时候地图中可能需要添加指南针（这个主要取决于地图的投影），GMT提供了这样的命令。使用的命令是pscoast程序中 -T开关。具体如下： [ −T[f|m][x]lon0/lat0/size[/info][:w,e,s,n:][+gint[/mint]] ]Draws a simple map directional rose centered on lon0/lat0. Use −Tx to specify x/y position instead. The size is the diameter of the rose, and optional label information can be specified to override the default values of W, E, S, and N (Give :: to suppress all labels). The default map rose only labels north. Use −Tf to get a "fancy" rose, and specify in info what you want drawn. The default draws the two principal E-W, N-S orientations, 2 adds the two intermediate NW-SE and NE-SW orientations, while 3 adds the eight minor orientations WNW-ESE, NNW-SSE, NNE-SSW, and ENE-WSW. For a magnetic compass rose, specify −Tm. If given, info must be the two parameters dec/dlabel, where dec is the magnetic declination and dlabel is a label for the magnetic compass needle (specify - to format a label from dec). Then, both directions to geographic and magnetic north are plotted . If the north label is * then a north star is plotted instead of the north label. Annotation and two levels of tick intervals for geographic and magnetic directions are 10/5/1 and 30/5/1 degrees, respectively; override these settings by appending +gints[/mints]. Color and pen attributes are taken from and , respectively, while label fonts and sizes follow the usual annotation, label, and header font settings.例子：pscoast -Tf130/25/0.8i/1-R110/135/20/50 -JM5i -P -N1/0.8p -B5g5 -W1/0.8p >output.ps
细节的修改，如指南针的样式，NSWE大小和颜色的修改等，也可以依据需要设置。
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