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:
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.
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.
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.
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.
ARC/INFO DLG data is handled in a slightly different manner.
Some DLG files may or may NOT have this and processing will be required to handle each case differently.
- OR -
If the DLG does contain category codes, then the ASCII DLG file is converted to a binary DLG file.
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:
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.
Last changed: $Date: 2003/03/24 08:02:46 $