Compilation and Installation of PSSAC on Linux

pssac是朱露培老師所寫的小程式，是一個特別設計跟gmt參數相同的程式，適合寫在GMT script裡直接繪出sac圖形的有用工具。一年多前嘗試想要編譯成功他，卻一直沒有成功。今年彷彿又聽到大家有使用pssac的需求，於是提筆寫信問朱教授。朱教授熱心的回應，使我終於成功編譯pssac。

首先，你的linux/unix主機必須有gcc任何的c編譯器。
第二，你需要先安裝好GMT；GMT的安裝請參考GMT簡易安裝筆記。新版的GMT已經到4.5.5，但是安裝form大致上是一樣的。
第三，請到朱教授的個人網站下載pssac的原始碼。如果你的GMT版本是4.5以上，還請多下載新的pssac.c取代原本tar裡的檔案。
假設我們安裝好的GMT路徑是/opt/GMT4.5.2，netcdf的路徑為/opt/netcdf-3.6.3:

tar xvf pssac.tar
cd pssac; mv pssac.c pssac-old.c
wget -c http://www.eas.slu.edu/People/LZhu/downloads/pssac.c

不過直接使用原本的Makefile編譯成功的機會恐怕很少。請修改Makefile成如下的樣子：

1. CC = gcc
2. GMT_INC = -I /opt/GMT4.5.2/include -I /opt/netcdf-3.6.3/include
3. GMT_LIBS = -L /opt/GMT4.5.2/lib -L /opt/netcdf-3.6.3/lib -lgmt -lgmtps -lpsl -lnetcdf -lm -s
4. CFLAGS = -O2 ${GMT_INC}
5.  
6. pssac: pssac.o sacio.o
7.     ${CC} -o $@ $@.o sacio.o ${GMT_LIBS} ${CFLAGS}
8.  
9. clean:
10.     @rm -f pssac *.o

接著請執行make。如果你有確實的寫對GMT以及netcdf的函式庫位置以及headers的位置，你應該可以看到如下的輸出：

gcc -O2 -I /opt/GMT4.5.2/include -I /opt/netcdf-3.6.3/include -c -o pssac.o pssac.c
gcc -O2 -I /opt/GMT4.5.2/include -I /opt/netcdf-3.6.3/include -c -o sacio.o sacio.c
gcc -o pssac pssac.o sacio.o -L /opt/GMT4.5.2/lib -L /opt/netcdf-3.6.3/lib -lgmt -lgmtps -lpsl -lnetcdf -lm -s -O2 -I /opt/GMT4.5.2/include -I /opt/netcdf-3.6.3/include

然而當你想要試著執行他的時候卻出現錯誤訊息：

./pssac: error while loading shared libraries: libnetcdf.so.4: cannot open shared object file: No such file or directory

可知pssac執行時期需要libnetcdf.so.4這個函式，利用find指令可以發現這個檔案就在/etc/netcdf-3.6.3/lib裡。原來是系統並不認識他，趕快加進來吧(別忘了切到root身份)！

echo "/opt/netcdf-3.6.3/lib" > /etc/ld.so.conf.d/libnetcdf.conf
echo "/opt/GMT4.5.2/lib" > /etc/ld.so.conf.d/libgmt.conf
ldconfig

此時再執行pssac試試看：

Usage: pssac standardGMToptions [SACfiles] [-C[t1/t2]] [-E(k|d|a|n|b)(t[n]|vel)] [-Gr/g/b/c] [-I] [-Msize[/alpha]] [-Q] [-r] [-Sshift] [-V]

    pssac plots SAC traces. If no SAC file names is provided in the command line, it expects (sacfile,[x,[y [pen]]) from stdin.
       -C only plot data between t1 and t2
       -E option determines
         (1) profile type:
   a: azimuth profile
   b: back-azimuth profiel
   d: epicentral distance (in degs.) profile
   k: epicentral distance (in km.) profile
   n: traces are numbered from 1 to N in y-axis
         (2) time alignment:
   tn: align up with time mark tn in SAC head
              default is the reference time. Others are
       n= -5(b), -3(o), -2(a), 0-9 (t0-t9)
   vel: use reduced velocity
       -G paint amplitudes larger than c with color r/g/b
       -I integrate the trace before plotting
       -M multiple traces
   size: each trace will normalized to size (in y-unit)
   size/alpha: if alpha<0, use same scale for all traces
       else plot absolute amplitude multiplied by size*r^alpha
       where r is the distance range in km
       -Q square the trace
       -r remove the mean value in the trace
       -S shift traces by shift seconds
       -V plot traces vertically

確定可以執行後，把他放到/usr/local/bin裡，這樣所有使用者都可以使用這隻程式啦！

再次感謝朱老師的熱心幫忙！

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