질문 :  
     GRASS에서 CELL driver 의 기능과 의미는 무엇인가 ?

답변 :  
 CELL driver는 모니터  출력 대신에 파일 출력을 지원하는 
 드라이브이다. 
 다음과 같은 용도로 사용된다 :

     - 모니터 해상도보다 높은 이미지를 파일로 저장하는 용도.
     - d.3d 명령을 통해 생성된 3차원 영상을 파일로 저장하는 용도.
     - raster/raster/vector/...등이 중첩되어 있는 도면을 하나로 
       합쳐서 r.out.tiff등의 명령에 사용될 파일을 만드는 용도.

 You will find a "D_cell" raster file in your GRASS database 
 after starting the driver, using d.rast, d.vect etc.(find some
 hints for d.3d and CELL driver) and
 stopping the driver again.
 Then you can export this file through r.out.tiff etc. into
 your mapping program (xfig or what you like) or may use it 
 with p(s).map.

 Be aware that "D_cell" is in a different projecting that the
 usual raster files and can be displayed on a GRASS monitor only
 with a trick.

 Usage in details:

  Set the raster file size for CELL driver
       ATTENTION: You have to add 1 to xxx to get your resolution 
              (strange thing..)

     export GRASS_WIDTH=xxx    #if you want another size than the default 640
     export GRASS_HEIGHT=xxx   #if you want another size than the default 480

         Example: You want 640x480:
                    export GRASS_WIDTH=641
                    export GRASS_HEIGHT=481

     If "export" is not accepted in your shell, try "setenv" instead:
                    setenv GRASS_WIDTH 641
                    setenv GRASS_HEIGHT 481



     d.mon start=CELL     # Wait for "Ready" message (may take some time due
                                                  to the file size selected)
     d.mon select=CELL

     d.yyyy               # use your display command (you will see nothing
      (d.rast, d.vect,       certainly, because the output is directed into
       d.3d,...)             the file D_cell)
                            -> use -o flag for second, third raster overlay!

     d.mon stop=CELL      # now the D_cell file is written (will also take
                                time, wait for CPU/Harddisk getting ready)

     
 - If you like: Look at the file

           use a trick:
              g.region raster=D_cell # this sets the region to 
                                         CELL projection
              d.mon start=x0         # start after using g.region
              d.rast D_cell          # should work...
              d.mon stop=x0          # stop it (it is in D_cell projection)
              g.region -d            # don't forget to reset the
                                         location afterwards
              d.mon start=x0         # start after using g.region -d
                                              if you want to display usual maps
                   
         (Hint: If you already have started a X-monitor, use d.mon select=x0
            and d.erase after the g.region commands instead of starting and 
            stopping the X-Monitors.)

 - If you like: Export the file
              g.region raster=D_cell  # set the region to CELL
              r.out.tiff [-p] input=D_cell output=D_cell.tiff  
                          # use -p for 8bit instead of 24bit TIFF export
              g.region -d             # reset the region to your coordinates



 Many thanks to Michel Wurtz - LTE  for his hints!

 
Markus Neteler
neteler@geog.uni-hannover.de
20. Jan. 1999
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