自動抓取RMT的圖檔

RMT的公開資料，是從自由場（加速度感測器）取得，主要是用來計算地震當下的參數。從好幾次的觀察經驗得知，出震前1天到幾個小時，會有一些特殊的特徵波型，尤其是越大的地震會越明顯。目前中研院只用瞬間或很短的時間資料來計算，沒有用到震前幾小時的資料，因此可以研究一下如何利用這些資料來計算震前的現象。

這個簡單的java程式，從RMT網站抓取圖檔，以每日/每小時分目錄置放，估計一天約有4.7GB的資料量。這些圖檔未來可進行OCR辨識，將數值還原成文字資料，或是以其他圖訊辨識技術，計算震前的特徵。使用本程式前，須先安裝 Java SDK，使用javac編譯後，再用java來執行。程式會呼叫外部wget程式，因此亦須安裝 wget，Linux系統直接安裝即可，Windows系統可用GnuWin32的http://gnuwin32.sourceforge.net/packages/wget.htm，安裝後一樣要設定系統PATH才能被呼叫。為了準確地2秒抓一次圖，每2秒產生一個執行緒，每個抓圖執行緒應會在0.1秒內完成，如果失敗的話，圖檔的內容會不正常，便於瞭解錯誤狀況，若不需要可另加程式自動刪除。

import java.text.*; import java.util.*; import java.io.*; public class RMT {         public static void main(String[] args)         {                 while (true) {                         try {                                 downloadThread thread = new downloadThread();                                 thread.start();                                                         Thread.sleep(2000);                         } catch(InterruptedException ex) {                                 Thread.currentThread().interrupt();                         }                 }         } } class downloadThread extends Thread{         public void run(){                 downloadRMT();         }                   void downloadRMT()         {                 Date now = new java.util.Date();                 String dirTodayName = new SimpleDateFormat("yyyyMMdd").format(now);                 String dirHourName  = new SimpleDateFormat("HH").format(now);                 String filename = new SimpleDateFormat("yyyyMMdd-HHmmss").format(now) + ".png";                              String filepath =  dirTodayName + "/" + dirHourName + "/" + filename;                                 File dirToday = new File(dirTodayName);         if (!dirToday.exists()) {             boolean success = dirToday.mkdir();             if (success) {                 System.out.printf("Successfully created new directory : %s%n", dirTodayName);             } else {                 System.out.printf("Failed to create new directory: %s%n", dirTodayName);             }         }                                 File dirHour = new File(dirTodayName + "/" + dirHourName);         if (!dirHour.exists()) {             boolean success = dirHour.mkdir();             if (success) {                 System.out.printf("Successfully created new directory : %s%n", dirHourName);             } else {                 System.out.printf("Failed to create new directory: %s%n", dirHourName);             }         }                                 try {                        Runtime rt = Runtime.getRuntime ();                         String command = "wget http://rmt.earth.sinica.edu.tw/rmt.png -O " + filepath;                         System.out.println (command);             Process proc = rt.exec (command);                         int exitCode = proc.waitFor ();                         if (exitCode==0) {                                 //System.out.println ("OK");                         } else {                                 System.out.println ("Fail : Code = " + exitCode);                         }                                 } catch (Exception e) {             e.printStackTrace();         }                       } }