3 Arc Second Digital Elevation Data

This file discusses the programs and utilities for extracting and processing data from the 3 Arc Second Digital Elevation Map data for the United States.

Unless otherwise noted:

File Contents

DIGITAL ELEVATION MODEL FILES

File Naming Conventions:

Each file on the CDs has the following format for its name:

xxyyy.3CD;1
where

So, the actual file name (from the CD) for the sample data under item 1 (previous section) would be "31098.3CD;1".

If I wanted to extract, for example, the file "31098.3CD;1", I would do the following:

  1. Note that it would be on the 3rd CD.
  2. Note that it was in the CD3_DIR5 directory.
What's on the CDs:

Reading Files from Tape:

  1. Put the tape into the (hardware-)compressing tape drive.
  2. Operate from hydro1 (not a hydro4 window on hydro1's console).
  3. Figure out which CD the file was on (you can figure out the CD number by reading README.genl). Call the CD number x (where x varies from 1 to 6).
  4. Rewind the tape (to be safe) with 'mt -t /dev/rmt/5m rew'.
  5. if x > 1
    let y = x - 1
    then 'mt -t /dev/rmt/5mn fsf y' -- the n in '5mn' is so it don't rewind
    else
    goto step 5
    end if
  6. To read a single file from tape: 
    'gtar xvbf 128 /dev/rmt/5m cdrom/CDx_DIRz/LLMMM.3CD\;1'
                                   ^    ^ ^ ^
            x is still the CD number    | | |
  z is the directory the file is found in | |
                         LL is the latitude |
    MMM is the longitude (might begin with 0)

PROCESSING DIGITAL ELEVATION MODEL DATA

UTILITY PROGRAMS

Extracting a Region from the DEM:

The program 3cd2asc will extract a region from a single DEM file, defined by latitudes and longitudes (keep seconds in multiples of 30).

Extracting the Walnut River Region:

This program was developed specifically for extracting the region of the Walnut River basin used for the CASES project. It requires the 4 raw DEM files, that encompass the Walnut River Basin. These will be properly rotated, and then the desired region will be extracted and the pieces will be assembled into the complete file.

Hydrology Homepage / University of Washington / hydro@hydro.washington.edu