ITCHy GRASS problem with DEM tapework
Michael Shapiro
shapiro at zorro.cecer.army.mil
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
(rmt0).
(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 r.support 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.erase
d.rast <name>
-----------------------------------------------------------------
Michael Shapiro U.S. Army CERL
email: shapiro at zorro.cecer.army.mil Environmental Division
phone: (217) 352-6511 ext 526 P.O. Box 9005
fax: (217) 373-7222 Champaign, Ill. 61826-9005
-----------------------------------------------------------------
More information about the grass-user
mailing list