GMT中的 surface
在gmt中由xyz文件转到grid的文件有两个主要命令：xyz2grd, surface,前面已经提到xyz2grd，xyz2grd要求等间隔采样，有时候显得很不方便。而surface可以提供一个较好的方式Adjustable tension continuous curvature surface gridding
可调整的曲线表面网格？由manual给出的解释是 A continuous curvature gridding algorithm 应该可以理解为曲率连续的网格插值算法，具体的例子在cookbook的6.14，6.16都有用到
主要选项：
surface -G -I[/]
-R/// [-A] [-C]
[-H[]] [-Ll] [-L] [-N] ] [-S]
[-T ] [-Q] [-V] [-Z] [-:] [-bi[]]
-G 输出文件名
-xinc/yinc: 给出插值后的网格间隔
-R：指定坐标范围
-A：
-Z：是插值的收敛标准
-L：？强行指定解的范围？
without any modifiers indicate that x is longitude and periodic in 360:
-L constrain the range of output values:
-Ll specifies lower limit; forces solution to be >= .
-Lu specifies upper limit; forces solution to be <= .
can be any number, or the letter d for min (or max) input data value,
or the filename of a grdfile with bounding values. .
Example: -Ll0 gives a non-negative solution.
-N sets max in each cycle; default = 250.
设置每个圆的最大迭代数
-S 除非网格是病态的
sets to initialize grid; default = 0 will skip this step.
This step is slow and not needed unless grid dimensions are pathological;
i.e., have few or no common factors.
Append m to give in minutes.
-T adds Tension to the gridding equation; use a value between 0 and 1.
default = 0 gives minimum curvature (smoothest; bicubic) solution.
1 gives a harmonic spline solution (local max/min occur only at data points).
typically 0.25 or more is good for potential field (smooth) data;
0.75 or so for topography. Experiment.
Append B or b to set tension in boundary conditions only;
Append I or i to set tension in interior equations only;
关系到插值的结果？详情见cookboo 6.16图
-Z sets . Default = 1.4
Use a value between 1 and 2. Larger number accelerates convergence but can be unstable.
Use 1 if you want to be sure to have (slow) stable convergence.
控制收敛速度
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