v.in.dlg - Converts an ASCII USGS DLG-3 Optional
file to a binary GRASS vector (dig) file.
(GRASS Vector Data Import Program)
v.in.dlg [-l] input=name
This program converts an ASCII USGS DLG-3
into a binary GRASS vector (dig) file. Store
the DLG-file into $LOCATION/dlg/ (create this directory, if
not there) before importing.
Warning: The program reads DLG-3 Optional format
v.in.dlg also creates a dig_att file
containing the label information 'stripped' from the DLG-3
file (the first minor attribute for each record unless
matt is specified).
If the matt is specified, v.in.dlg creates an additional
attribute file containing identifiers for every record with correspon
multiple attributes. In this case matt file contains identifiers
starting with base base for the attributes stored in matt
file (as opposed to the first minor attributes with no matt file).
The example of matt with base = 34 would be:
34 0 0
35 180 201
36 180 208
37 160 220
With the corresponding dig_att looking like this:
A 648467.190000 4456367.320000 34
L 667989.290000 4458393.520000 35
L 651002.470000 4473793.390000 36
L 663816.680000 4471412.080000 37
However, the user must run
option 4) on the output file created by
v.in.dlg to create a dig_plus file
containing the file topology, before using the
output file in
The user can avoid this two-step process by converting
the ASCII DLG-3 file to binary GRASS vector format
using option 1 of the GRASS program
- Give precedence to line information (default is area).
- Name of USGS DLG-3 Optional format input file.
- Name to be assigned to the binary GRASS vector files created.
- Name of file with multiple attributes (optional).
- Identifier base for multiple attributes (default is 1).
If the user simply types v.in.dlg without specifying
parameter values on the command line, the program will
prompt the user to enter these.
Area vs Line Precedence:
Some machine-processed DLG-3 files do not make the
distinction between line edges and area edges. For
example, in a roads map, where the desired information is
line edge data, a downtown block surrounded by roads may be
processed as an area. Because of this, the user is asked
to choose whether to give precedence to areas or lines. If
precedence is given to lines, the user should be aware that
any lines that bound unlabeled areas in the DLG-3 file will
be stored as line data. Any unlabeled areas would
therefore be lost (this is only a concern when areas are
unlabeled; labeled area information will be retained). If
precedence is given to areas, lines will be stored as
boundaries to areas that are unlabeled.
Building support files with
When you run
you will have the option of snapping the nodes in your
vector file that fall within a certain threshold of one
another. WARNING: the default threshold is calculated
using the scale of the original DLG-3 file. If the
threshold is too high, excessive snapping may occur,
destroying the file!! With
the user has the option of snapping or not snapping nodes,
and further, of setting a particular snapping threshold.
U.S.Army Construction Engineering
Irina Kosinovsky, U.S.Army Construction Engineering