ITCHy GRASS problem with DEM tapework

Michael Shapiro shapiro at
Sun Mar 22 09:48:25 EST 1992

(a) m.dem.examine is broken. Only m.dem.extract  has  been  fixed
and  that  occured  after  4.0 was released. In any case I highly
doubt these programs will work with other than dem 9-track  tapes

(b) m.examine.tape should be used with some care. If you tell  it
blocksize=8192 then it will nmever see a record larger than that.
Try a larger blocksize just to be sure that the data really  only
has 8192 bytes per physical record

(c) To extract the data don't use GRASS  programs.  Use  dd  with
approriate  parameters  to  extract  each  dem  into a rater file
directly. Then use to create an appropriate header file
(by hand) - g.region will be of no use to dd. The issues you need
to look into are
  (1) #bytes per cell - most likely 2 since it is elevation data
  (2) byte ordering - if not MSB-LSB then you will need to swap
      bytes with dd as you extract the files.

(d) When displaying the dem raster maps you have just made, match
your  region to the raster header to make sure you are seeing the
raster map exactly (rather  than  some  subset  or  perhaps  even
looking off the map). This is done by:
   g.region rast=<name>
   d.rast <name>

Michael Shapiro                        U.S. Army CERL                  
email:   shapiro at  Environmental Division          
phone:   (217) 352-6511  ext 526       P.O. Box 9005                   
fax:     (217) 373-7222                Champaign, Ill. 61826-9005

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