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 [xyz-file] -G<output_grdfile_name> -I<xinc>[m|c][/<yinc>[m|c]]
        -R<west>/<east>/<south>/<north> [-A<aspect_ratio>] [-C<convergence_limit>]
        [-H[<nrec>]] [-Ll<limit>] [-L[u<limit>]] [-N<n_iterations>] ] [-S<search_radius>[m]]
        [-T<tension>[i][b] ] [-Q] [-V[l]] [-Z<over_relaxation_parameter>] [-:] [-bi[s][<n>]]
-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<limit> specifies lower limit; forces solution to be >= <limit>.
                -Lu<limit> specifies upper limit; forces solution to be <= <limit>.
                <limit> can be any number, or the letter d for min (or max) input data value,
                or the filename of a grdfile with bounding values. [Default solution unconstrained].
                Example: -Ll0 gives a non-negative solution.

-N     sets max <n_iterations> 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 <search_radius> 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 <search_radius> 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 <over_relaxation parameter>. 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