在C程序中读写SU格式文件
文章目录
序言
Seismic_Unix是处理勘探地震数据的好工具，SU文件格式是其内部的默认格式，有时候需要自己在程序 中读写SU文件。本文介绍如何在C程序中读写SU格式文件。
子函数库
Seismic_Unix程序自带有子函数库，但是我没有找到相关的程序源码。。。。
但是其中自带的 segy.h 头文件可以帮助我们了解SU文件的道头格式，而且可以利用该头文件
来对SU格式的文件进行读写。
关于SU文件格式可以参考SU/SEGY文件格式 一文。
在 segy.h 中定义了名为 segy 的结构体，其包含了SU格式的所有道头变量。
/* Copyright (c) Colorado School of Mines, 2011.*/
/* All rights reserved. */
/* segy.h - include file for SEGY traces
*
* declarations for:
* typedef struct {} segy - the trace identification header
* typedef struct {} bhed - binary header
*
* Note:
* If header words are added, run the makefile in this directory
* to recreate hdr.h.
*
* Reference:
* K. M. Barry, D. A. Cavers and C. W. Kneale, "Special Report:
* Recommended Standards for Digital Tape Formats",
* Geophysics, vol. 40, no. 2 (April 1975), P. 344-352.
*
* $Author: john $
* $Source: /usr/local/cwp/src/su/include/RCS/segy.h,v $
* $Revision: 1.33 $ ; $Date: 2011/11/11 23:56:14 $
*/
#include <limits.h>
#include "par.h"
#ifndef SEGY_H
#define SEGY_H
#define TRCBYTES 240
#define SU_NFLTS 32767 /* Arbitrary limit on data array size */
/* TYPEDEFS */
typedef struct { /* segy - trace identification header */
int tracl; /* Trace sequence number within line
--numbers continue to increase if the
same line continues across multiple
SEG Y files.
byte# 1-4
*/
int tracr; /* Trace sequence number within SEG Y file
---each file starts with trace sequence
one
byte# 5-8
*/
int fldr; /* Original field record number
byte# 9-12
*/
int tracf; /* Trace number within original field record
byte# 13-16
*/
int ep; /* energy source point number
---Used when more than one record occurs
at the same effective surface location.
byte# 17-20
*/
int cdp; /* Ensemble number (i.e. CDP, CMP, CRP,...)
byte# 21-24
*/
int cdpt; /* trace number within the ensemble
---each ensemble starts with trace number one.
byte# 25-28
*/
short trid; /* trace identification code:
-1 = Other
0 = Unknown
1 = Seismic data
2 = Dead
3 = Dummy
4 = Time break
5 = Uphole
6 = Sweep
7 = Timing
8 = Water break
9 = Near-field gun signature
10 = Far-field gun signature
11 = Seismic pressure sensor
12 = Multicomponent seismic sensor
- Vertical component
13 = Multicomponent seismic sensor
- Cross-line component
14 = Multicomponent seismic sensor
- in-line component
15 = Rotated multicomponent seismic sensor
- Vertical component
16 = Rotated multicomponent seismic sensor
- Transverse component
17 = Rotated multicomponent seismic sensor
- Radial component
18 = Vibrator reaction mass
19 = Vibrator baseplate
20 = Vibrator estimated ground force
21 = Vibrator reference
22 = Time-velocity pairs
23 ... N = optional use
(maximum N = 32,767)
Following are CWP id flags:
109 = autocorrelation
110 = Fourier transformed - no packing
xr[0],xi[0], ..., xr[N-1],xi[N-1]
111 = Fourier transformed - unpacked Nyquist
xr[0],xi[0],...,xr[N/2],xi[N/2]
112 = Fourier transformed - packed Nyquist
even N:
xr[0],xr[N/2],xr[1],xi[1], ...,
xr[N/2 -1],xi[N/2 -1]
(note the exceptional second entry)
odd N:
xr[0],xr[(N-1)/2],xr[1],xi[1], ...,
xr[(N-1)/2 -1],xi[(N-1)/2 -1],xi[(N-1)/2]
(note the exceptional second & last entries)
113 = Complex signal in the time domain
xr[0],xi[0], ..., xr[N-1],xi[N-1]
114 = Fourier transformed - amplitude/phase
a[0],p[0], ..., a[N-1],p[N-1]
115 = Complex time signal - amplitude/phase
a[0],p[0], ..., a[N-1],p[N-1]
116 = Real part of complex trace from 0 to Nyquist
117 = Imag part of complex trace from 0 to Nyquist
118 = Amplitude of complex trace from 0 to Nyquist
119 = Phase of complex trace from 0 to Nyquist
121 = Wavenumber time domain (k-t)
122 = Wavenumber frequency (k-omega)
123 = Envelope of the complex time trace
124 = Phase of the complex time trace
125 = Frequency of the complex time trace
130 = Depth-Range (z-x) traces
201 = Seismic data packed to bytes (by supack1)
202 = Seismic data packed to 2 bytes (by supack2)
byte# 29-30
*/
short nvs; /* Number of vertically summed traces yielding
this trace. (1 is one trace,
2 is two summed traces, etc.)
byte# 31-32
*/
short nhs; /* Number of horizontally summed traces yielding
this trace. (1 is one trace
2 is two summed traces, etc.)
byte# 33-34
*/
short duse; /* Data use:
1 = Production
2 = Test
byte# 35-36
*/
int offset; /* Distance from the center of the source point
to the center of the receiver group
(negative if opposite to direction in which
the line was shot).
byte# 37-40
*/
int gelev; /* Receiver group elevation from sea level
(all elevations above the Vertical datum are
positive and below are negative).
byte# 41-44
*/
int selev; /* Surface elevation at source.
byte# 45-48
*/
int sdepth; /* Source depth below surface (a positive number).
byte# 49-52
*/
int gdel; /* Datum elevation at receiver group.
byte# 53-56
*/
int sdel; /* Datum elevation at source.
byte# 57-60
*/
int swdep; /* Water depth at source.
byte# 61-64
*/
int gwdep; /* Water depth at receiver group.
byte# 65-68
*/
short scalel; /* Scalar to be applied to the previous 7 entries
to give the real value.
Scalar = 1, +10, +100, +1000, +10000.
If positive, scalar is used as a multiplier,
if negative, scalar is used as a divisor.
byte# 69-70
*/
short scalco; /* Scalar to be applied to the next 4 entries
to give the real value.
Scalar = 1, +10, +100, +1000, +10000.
If positive, scalar is used as a multiplier,
if negative, scalar is used as a divisor.
byte# 71-72
*/
int sx; /* Source coordinate - X
byte# 73-76
*/
int sy; /* Source coordinate - Y
byte# 77-80
*/
int gx; /* Group coordinate - X
byte# 81-84
*/
int gy; /* Group coordinate - Y
byte# 85-88
*/
short counit; /* Coordinate units: (for previous 4 entries and
for the 7 entries before scalel)
1 = Length (meters or feet)
2 = Seconds of arc
3 = Decimal degrees
4 = Degrees, minutes, seconds (DMS)
In case 2, the X values are longitude and
the Y values are latitude, a positive value designates
the number of seconds east of Greenwich
or north of the equator
In case 4, to encode +-DDDMMSS
counit = +-DDD*10^4 + MM*10^2 + SS,
with scalco = 1. To encode +-DDDMMSS.ss
counit = +-DDD*10^6 + MM*10^4 + SS*10^2
with scalco = -100.
byte# 89-90
*/
short wevel; /* Weathering velocity.
byte# 91-92
*/
short swevel; /* Subweathering velocity.
byte# 93-94
*/
short sut; /* Uphole time at source in milliseconds.
byte# 95-96
*/
short gut; /* Uphole time at receiver group in milliseconds.
byte# 97-98
*/
short sstat; /* Source static correction in milliseconds.
byte# 99-100
*/
short gstat; /* Group static correction in milliseconds.
byte# 101-102
*/
short tstat; /* Total static applied in milliseconds.
(Zero if no static has been applied.)
byte# 103-104
*/
short laga; /* Lag time A, time in ms between end of 240-
byte trace identification header and time
break, positive if time break occurs after
end of header, time break is defined as
the initiation pulse which maybe recorded
on an auxiliary trace or as otherwise
specified by the recording system
byte# 105-106
*/
short lagb; /* lag time B, time in ms between the time break
and the initiation time of the energy source,
may be positive or negative
byte# 107-108
*/
short delrt; /* delay recording time, time in ms between
initiation time of energy source and time
when recording of data samples begins
(for deep water work if recording does not
start at zero time)
byte# 109-110
*/
short muts; /* mute time--start
byte# 111-112
*/
short mute; /* mute time--end
byte# 113-114
*/
unsigned short ns; /* number of samples in this trace
byte# 115-116
*/
unsigned short dt; /* sample interval; in micro-seconds
byte# 117-118
*/
short gain; /* gain type of field instruments code:
1 = fixed
2 = binary
3 = floating point
4 ---- N = optional use
byte# 119-120
*/
short igc; /* instrument gain constant
byte# 121-122
*/
short igi; /* instrument early or initial gain
byte# 123-124
*/
short corr; /* correlated:
1 = no
2 = yes
byte# 125-126
*/
short sfs; /* sweep frequency at start
byte# 127-128
*/
short sfe; /* sweep frequency at end
byte# 129-130
*/
short slen; /* sweep length in ms
byte# 131-132
*/
short styp; /* sweep type code:
1 = linear
2 = cos-squared
3 = other
byte# 133-134
*/
short stas; /* sweep trace length at start in ms
byte# 135-136
*/
short stae; /* sweep trace length at end in ms
byte# 137-138
*/
short tatyp; /* taper type: 1=linear, 2=cos^2, 3=other
byte# 139-140
*/
short afilf; /* alias filter frequency if used
byte# 141-142
*/
short afils; /* alias filter slope
byte# 143-144
*/
short nofilf; /* notch filter frequency if used
byte# 145-146
*/
short nofils; /* notch filter slope
byte# 147-148
*/
short lcf; /* low cut frequency if used
byte# 149-150
*/
short hcf; /* high cut frequncy if used
byte# 151-152
*/
short lcs; /* low cut slope
byte# 153-154
*/
short hcs; /* high cut slope
byte# 155-156
*/
short year; /* year data recorded
byte# 157-158
*/
short day; /* day of year
byte# 159-160
*/
short hour; /* hour of day (24 hour clock)
byte# 161-162
*/
short minute; /* minute of hour
byte# 163-164
*/
short sec; /* second of minute
byte# 165-166
*/
short timbas; /* time basis code:
1 = local
2 = GMT
3 = other
byte# 167-168
*/
short trwf; /* trace weighting factor, defined as 1/2^N
volts for the least sigificant bit
byte# 169-170
*/
short grnors; /* geophone group number of roll switch
position one
byte# 171-172
*/
short grnofr; /* geophone group number of trace one within
original field record
byte# 173-174
*/
short grnlof; /* geophone group number of last trace within
original field record
byte# 175-176
*/
short gaps; /* gap size (total number of groups dropped)
byte# 177-178
*/
short otrav; /* overtravel taper code:
1 = down (or behind)
2 = up (or ahead)
byte# 179-180
*/
#ifdef SLTSU_SEGY_H /* begin Unocal SU segy.h differences */
/* cwp local assignments */
float d1; /* sample spacing for non-seismic data
byte# 181-184
*/
float f1; /* first sample location for non-seismic data
byte# 185-188
*/
float d2; /* sample spacing between traces
byte# 189-192
*/
float f2; /* first trace location
byte# 193-196
*/
float ungpow; /* negative of power used for dynamic
range compression
byte# 197-200
*/
float unscale; /* reciprocal of scaling factor to normalize
range
byte# 201-204
*/
short mark; /* mark selected traces
byte# 205-206
*/
/* SLTSU local assignments */
short mutb; /* mute time at bottom (start time)
bottom mute ends at last sample
byte# 207-208
*/
float dz; /* depth sampling interval in (m or ft)
if =0.0, input are time samples
byte# 209-212
*/
float fz; /* depth of first sample in (m or ft)
byte# 213-116
*/
short n2; /* number of traces per cdp or per shot
byte# 217-218
*/
short shortpad; /* alignment padding
byte# 219-220
*/
int ntr; /* number of traces
byte# 221-224
*/
/* SLTSU local assignments end */
short unass[8]; /* unassigned
byte# 225-240
*/
#else
/* cwp local assignments */
float d1; /* sample spacing for non-seismic data
byte# 181-184
*/
float f1; /* first sample location for non-seismic data
byte# 185-188
*/
float d2; /* sample spacing between traces
byte# 189-192
*/
float f2; /* first trace location
byte# 193-196
*/
float ungpow; /* negative of power used for dynamic
range compression
byte# 197-200
*/
float unscale; /* reciprocal of scaling factor to normalize
range
byte# 201-204
*/
int ntr; /* number of traces
byte# 205-208
*/
short mark; /* mark selected traces
byte# 209-210
*/
short shortpad; /* alignment padding
byte# 211-212
*/
short unass[14]; /* unassigned--NOTE: last entry causes
a break in the word alignment, if we REALLY
want to maintain 240 bytes, the following
entry should be an odd number of short/UINT2
OR do the insertion above the "mark" keyword
entry
byte# 213-240
*/
#endif
} segy;
typedef struct { /* bhed - binary header */
int jobid; /* job identification number */
int lino; /* line number (only one line per reel) */
int reno; /* reel number */
short ntrpr; /* number of data traces per record */
short nart; /* number of auxiliary traces per record */
unsigned short hdt; /* sample interval in micro secs for this reel */
unsigned short dto; /* same for original field recording */
unsigned short hns; /* number of samples per trace for this reel */
unsigned short nso; /* same for original field recording */
short format; /* data sample format code:
1 = floating point, 4 byte (32 bits)
2 = fixed point, 4 byte (32 bits)
3 = fixed point, 2 byte (16 bits)
4 = fixed point w/gain code, 4 byte (32 bits)
5 = IEEE floating point, 4 byte (32 bits)
8 = two's complement integer, 1 byte (8 bits)
*/
short fold; /* CDP fold expected per CDP ensemble */
short tsort; /* trace sorting code:
1 = as recorded (no sorting)
2 = CDP ensemble
3 = single fold continuous profile
4 = horizontally stacked */
short vscode; /* vertical sum code:
1 = no sum
2 = two sum ...
N = N sum (N = 32,767) */
short hsfs; /* sweep frequency at start */
short hsfe; /* sweep frequency at end */
short hslen; /* sweep length (ms) */
short hstyp; /* sweep type code:
1 = linear
2 = parabolic
3 = exponential
4 = other */
short schn; /* trace number of sweep channel */
short hstas; /* sweep trace taper length at start if
tapered (the taper starts at zero time
and is effective for this length) */
short hstae; /* sweep trace taper length at end (the ending
taper starts at sweep length minus the taper
length at end) */
short htatyp; /* sweep trace taper type code:
1 = linear
2 = cos-squared
3 = other */
short hcorr; /* correlated data traces code:
1 = no
2 = yes */
short bgrcv; /* binary gain recovered code:
1 = yes
2 = no */
short rcvm; /* amplitude recovery method code:
1 = none
2 = spherical divergence
3 = AGC
4 = other */
short mfeet; /* measurement system code:
1 = meters
2 = feet */
short polyt; /* impulse signal polarity code:
1 = increase in pressure or upward
geophone case movement gives
negative number on tape
2 = increase in pressure or upward
geophone case movement gives
positive number on tape */
short vpol; /* vibratory polarity code:
code seismic signal lags pilot by
1 337.5 to 22.5 degrees
2 22.5 to 67.5 degrees
3 67.5 to 112.5 degrees
4 112.5 to 157.5 degrees
5 157.5 to 202.5 degrees
6 202.5 to 247.5 degrees
7 247.5 to 292.5 degrees
8 293.5 to 337.5 degrees */
short hunass[170]; /* unassigned */
} bhed;
/* DEFINES */
#define gettr(x) fgettr(stdin, (x))
#define vgettr(x) fvgettr(stdin, (x))
#define puttr(x) fputtr(stdout, (x))
#define vputtr(x) fvputtr(stdout, (x))
#define gettra(x, y) fgettra(stdin, (x), (y))
/* TOTHER represents "other" */
#define TOTHER -1
/* TUNK represents time traces of an unknown type */
#define TUNK 0
/* TREAL represents real time traces */
#define TREAL 1
/* TDEAD represents dead time traces */
#define TDEAD 2
/* TDUMMY represents dummy time traces */
#define TDUMMY 3
/* TBREAK represents time break traces */
#define TBREAK 4
/* UPHOLE represents uphole traces */
#define UPHOLE 5
/* SWEEP represents sweep traces */
#define SWEEP 6
/* TIMING represents timing traces */
#define TIMING 7
/* WBREAK represents timing traces */
#define WBREAK 8
/* NFGUNSIG represents near field gun signature */
#define NFGUNSIG 9
/* FFGUNSIG represents far field gun signature */
#define FFGUNSIG 10
/* SPSENSOR represents seismic pressure sensor */
#define SPSENSOR 11
/* TVERT represents multicomponent seismic sensor
- vertical component */
#define TVERT 12
/* TXLIN represents multicomponent seismic sensor
- cross-line component */
#define TXLIN 13
/* TINLIN represents multicomponent seismic sensor
- in-line component */
#define TINLIN 14
/* ROTVERT represents rotated multicomponent seismic sensor
- vertical component */
#define ROTVERT 15
/* TTRANS represents rotated multicomponent seismic sensor
- transverse component */
#define TTRANS 16
/* TRADIAL represents rotated multicomponent seismic sensor
- radial component */
#define TRADIAL 17
/* VRMASS represents vibrator reaction mass */
#define VRMASS 18
/* VBASS represents vibrator baseplate */
#define VBASS 19
/* VEGF represents vibrator estimated ground force */
#define VEGF 20
/* VREF represents vibrator reference */
#define VREF 21
/*** CWP trid assignments ***/
/* ACOR represents autocorrelation */
#define ACOR 109
/* FCMPLX represents fourier transformed - no packing
xr[0],xi[0], ..., xr[N-1],xi[N-1] */
#define FCMPLX 110
/* FUNPACKNYQ represents fourier transformed - unpacked Nyquist
xr[0],xi[0],...,xr[N/2],xi[N/2] */
#define FUNPACKNYQ 111
/* FTPACK represents fourier transformed - packed Nyquist
even N: xr[0],xr[N/2],xr[1],xi[1], ...,
xr[N/2 -1],xi[N/2 -1]
(note the exceptional second entry)
odd N:
xr[0],xr[(N-1)/2],xr[1],xi[1], ...,
xr[(N-1)/2 -1],xi[(N-1)/2 -1],xi[(N-1)/2]
(note the exceptional second & last entries)
*/
#define FTPACK 112
/* TCMPLX represents complex time traces */
#define TCMPLX 113
/* FAMPH represents freq domain data in amplitude/phase form */
#define FAMPH 114
/* TAMPH represents time domain data in amplitude/phase form */
#define TAMPH 115
/* REALPART represents the real part of a trace to Nyquist */
#define REALPART 116
/* IMAGPART represents the real part of a trace to Nyquist */
#define IMAGPART 117
/* AMPLITUDE represents the amplitude of a trace to Nyquist */
#define AMPLITUDE 118
/* PHASE represents the phase of a trace to Nyquist */
#define PHASE 119
/* KT represents wavenumber-time domain data */
#define KT 121
/* KOMEGA represents wavenumber-frequency domain data */
#define KOMEGA 122
/* ENVELOPE represents the envelope of the complex time trace */
#define ENVELOPE 123
/* INSTPHASE represents the phase of the complex time trace */
#define INSTPHASE 124
/* INSTFREQ represents the frequency of the complex time trace */
#define INSTFREQ 125
/* DEPTH represents traces in depth-range (z-x) */
#define TRID_DEPTH 130
/* 3C data... v,h1,h2=(11,12,13)+32 so a bitmask will convert */
/* between conventions */
/* CHARPACK represents byte packed seismic data from supack1 */
#define CHARPACK 201
/* SHORTPACK represents 2 byte packed seismic data from supack2 */
#define SHORTPACK 202
#define ISSEISMIC(id) (( (id)==TUNK || (id)==TREAL || (id)==TDEAD || (id)==TDUMMY || (id)==TBREAK || (id)==UPHOLE || (id)==SWEEP || (id)==TIMING || (id)==WBREAK || (id)==NFGUNSIG || ( id)==FFGUNSIG || (id)==SPSENSOR || (id)==TVERT || (id)==TXLIN || (id)==TINLIN || (id)==ROTVERT || (id)==TTRANS || (id)==TRADIAL || (id)==ACOR ) ? cwp_true : cwp_false )
/* FUNCTION PROTOTYPES */
#ifdef __cplusplus /* if C++, specify external linkage to C functions */
extern "C" {
#endif
/* get trace and put trace */
int fgettr(FILE *fp, segy *tp);
int fvgettr(FILE *fp, segy *tp);
void fputtr(FILE *fp, segy *tp);
void fvputtr(FILE *fp, segy *tp);
int fgettra(FILE *fp, segy *tp, int itr);
/* get gather and put gather */
segy **fget_gather(FILE *fp, cwp_String *key,cwp_String *type,Value *n_val,
int *nt,int *ntr, float *dt,int *first);
segy **get_gather(cwp_String *key, cwp_String *type, Value *n_val,
int *nt, int *ntr, float *dt, int *first);
segy **fput_gather(FILE *fp, segy **rec,int *nt, int *ntr);
segy **put_gather(segy **rec,int *nt, int *ntr);
/* hdrpkge */
void gethval(const segy *tp, int index, Value *valp);
void puthval(segy *tp, int index, Value *valp);
void getbhval(const bhed *bhp, int index, Value *valp);
void putbhval(bhed *bhp, int index, Value *valp);
void gethdval(const segy *tp, char *key, Value *valp);
void puthdval(segy *tp, char *key, Value *valp);
char *hdtype(const char *key);
char *getkey(const int index);
int getindex(const char *key);
void swaphval(segy *tp, int index);
void swapbhval(bhed *bhp, int index);
void printheader(const segy *tp);
void tabplot(segy *tp, int itmin, int itmax);
#ifdef __cplusplus /* if C++, end external linkage specification */
}
#endif
#endif
示例
假设我们现在想建立一个简单的一维水平层状模型，上层速度为2000 m/s， 下层速度为3000m/s。 将模型文件存储为SU格式。该模型大小为：2000m，深1000m。z和x方向的步长都为10。那么我们 可以通过以下程序来实现。
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include "segy.h"
int main(int argc, char *argv[])
{
FILE *fp_out;
size_t size, nwrite;
int n1, n2; // n1 number of samples; n2 number of traces
float d1, d2, f1, f2; // d1 samlping interval; d2 trace interval
float *data;
char file_out[30];
segy *hdrs;
n1 = 101; n2 = 201;
f1 = 0.0; f2 = 0.0;
d1 = 10.0; d2 = 10.0;
strcpy(file_out, argv[1]);
hdrs = (segy *)calloc(n2, sizeof(segy));
assert(hdrs != NULL);
for (int i=0; i<n2; i++) { // n2: number of traces
hdrs[i].f1 = f1;
hdrs[i].f2 = f2;
hdrs[i].d1 = d1;
hdrs[i].d2 = d2;
hdrs[i].ns = n1; //number of samples of this trace
hdrs[i].trwf = n2;
hdrs[i].tracl = i; // Trace sequence number within line
hdrs[i].tracf = i;
hdrs[i].scalco = -1000;
hdrs[i].gx = (i*d2)*1000;
hdrs[i].timbas = 3;
hdrs[i].trid = TRID_DEPTH; // trace identification code
}
size = n1*n2;
data = (float *)malloc(size * sizeof(float)); // the basic cell of data is float
assert(data != NULL);
for (int ix=0; ix<n2; ix++) {
for (int iz=0; iz<n1; iz++) {
if (iz < 50) {
data[ix*n1+iz] = 2000.0;
} else {
data[ix*n1+iz] = 3000.0;
}
}
}
// creat output file
fp_out = fopen(file_out, "w");
assert(fp_out != NULL);
for (int i=0; i<n2; i++) {
nwrite = fwrite(&hdrs[i], 1, TRCBYTES, fp_out); // TRCBYTES为segy.h中定义的SU文件的240字节头段大小。
assert(nwrite == TRCBYTES);
nwrite = fwrite(&data[i*n1], sizeof(float), n1, fp_out);
assert(nwrite == n1);
}
fclose(fp_out);
free(hdrs);
free(data);
return 0;
}
编译链接::
# 因为segy.h文件包含了par.h头文件，编译时，必须得找得到par.h文件才行
$ gcc -g -Wall -o test test.c -std=c99
# 运行
$ ./test first_model.su
就可以创建一个SU格式的速度格网文件。然后可以利用 suximage 命令来查看。
$ suximage <first_model.su title="Firts Model" wbox=1000 hbox=500 \
label2="lateral position [m]" label1="depth [m]" legend=1
后记
现在来说一说为什么要用SU格式来存储速度格网文件，直接用不带头段的二进制不好吗？
恩，答案就是不好！ 直接存二进制文件的话，因为文件本身是没有文件描述信息的，过一段时间
就忘了这个文件的格点数，横向和深度方向的大小什么的，很不方便。而且想画图看一下都不行。
二进制的文件得用 ximage 命令来查看，但是该命令必须指定一个维度的格点数才行。
而存成SU格式就没有这个问题了，头段相当于将该模型的格点信息等都存储着，想看的话，直接
用 suximage 命令即可。
PS： segy.h 里还有很多其他的函数在本文里没有涉及到。至于这些函数的功能，后面进一步学习之后
再拿出来讲。
修改历史
#. 2016-03-01 初稿 #. 2016-04-22 加入例子