NAME

v.import - SCS user interface to GRASS import programs.
(SCS GRASS Vector Program)

SYNOPSIS

v.import
v.import help

DESCRIPTION

This program performs all of the processes that are needed to convert ASCII DLG files and ASCII vector files into binary vector files. It also creates support files, the dig_plus file and the dig_att file (only created when importing DLG). The dig_plus file contains topological information obtained by analyzing the vector file. The dig_att file contains attribute information 'stripped' from the DLG file. This dig_att file is created for vector files by the labeling function of the GRASS v.digit program.
This command must be run interactively.

IMPORT FILES
After entering the command v.import, the user will be asked which type of file to import and create support files for: 

Imports to GRASS Vector Format and Creates Needed Support Files
   1  -   Ascii DLG file  to GRASS Vector Format
   2  -   Ascii VECTOR file  to GRASS Vector Format
   3  -   Binary VECTOR file to GRASS Vector Format

ASCII DLG File to GRASS Vector
Converts ASCII DLG files (such as those created in GRASS) to a vector file and creates the dig_plus and dig_att support files. The user is asked several questions:

  1. The name of the DLG data file.

    NOTE: It should be available in the $LOCATION/dlg directory. If the DLG data has an attribute flat file, it should also be in $LOCATION/dlg.

  2. Determine if this map is composed of Area or Line information.

    NOTE: Some machine-processed DLG files do not make the distinction between lines and area edges. For example, in a roads map, where the desired information is line 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 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.

  3. Determine if you want to snap nodes to other nodes within a threshold.

    NOTE: BE CAREFUL!!! This threshold is calculated using the scale of the original DLG or v.digit file. If the threshold is too high, excessive snapping may occur, destroying the file. In general, users seldom need to snap nodes. If snapping of nodes is desired, the user may want to run v.support separately. v.support allows the user to set the snapping threshold.

  4. Does the DLG data contain GRASS category codes?

    NOTE: Most non-GRASS computer systems will not be able to provide the necessary codes. The flat attribute file serves this purpose. If the answer to this question is NO:

    1. Enter a SUBJECT MATTER file name. A subject file will be used to assign GRASS category codes to the DLG data. It is structured the same as a dig_cats category file. It is suggested that a SUBJ directory be created in the GRASS location and a file containing all DLG attribute text labels by category be created. This will be required to provide consistency across several maps (quads) within one location. The user may use the vi text editor or the SCS macro make_subject to create it.

    2. Enter an ATTRIBUTE file name.

      This is the name of the flat file which will accompany a DLG from a non-GRASS system. This file contains all of the DLG area numbers with a corresponding text label.

    3. Is the DLG data from an ARC/INFO system.

      ARC/INFO DLG data is handled in a slightly different manner.

    4. Does The DLG contain a Universe Polygon.

      Some DLG files may or may NOT have this and processing will be required to handle each case differently.

      This process is done in three phases:

      1. If the DLG does NOT contain category codes, then a category file from the attribute file is created. Then the ASCII dlg file is converted to a binary dlg file.

        - OR -

        If the DLG does contain category codes, then the ASCII DLG file is converted to a binary DLG file.

      2. The binary dlg file is converted to a binary vector file, and the dig_att support file containing attribute information is created.

      3. The dig_plus support file is created by analyzing the vector file for topological information.

ASCII Vector File into GRASS Vector
Converts ASCII v.digit files (which are located in dig_ascii directory) into binary vector files and creates the dig_plus support file. Since a vector file keeps the distinction between lines and area edges, the user is not asked to give precedence to either. However, the user will be asked if the user wants to snap from nodes to other nodes within a calculated threshold.

This process is done in two phases:

  1. The ASCII vector file is converted to a binary vector file, and the dig_plus support file is created.

  2. The dig_plus support file is created by analyzing the vector file for topological information.

Binary Vector File to GRASS Vector
Creates the dig_plus support file.

This process is done in one phase: The dig_plus support file is created by analyzing the vector file for topological information.

SEE ALSO

v.in.dlg.scs
v.in.dlg
v.in.ascii
v.in.arc
v.in.dxf
v.in.tiger

AUTHOR

R.L.Glenn, USDA, SCS, NHQ-CGIS

Last changed: $Date$