v.in.arc.poly

NAME

v.in.arc.poly - Import areas from ARC/INFO ungenerate format.
(GRASS Vector Data Import Program)

SYNOPSIS

v.in.arc.poly ARC/INFO-file GRASS-vectorfile

OBJECTIVES:

The two programs and the shell-script are made for importing area data created by ARC/INFO-UNGENERATE to GRASS. The main problems when using v.in.arc followed by v.support directly are errors in the assignment of the area labels to the polygons. This is caused by polygons with identical starting points (first data pair), which are used for assigning the nodes. During this node creation in v.support the node of polygon 1 may be located within the area of polygon2 due to internal approximation processes. In this case, no area labels are assigned. To solve this problem, the whole file has to be scanned and searched for identical starting points. The coordinates of either one of the polygon-pairs with identical starting points have to be permutated. Then, during v.support, different nodes will be created and the assignment of the area labels will be done correctly.

STRUCTURE OF INPUT DATA

We have got our ARC/INFO files in the following format:

           1    3457065.250000    6095126.000000
    3457198.000000    6096357.500000
    3457459.750000    6095341.500000
    3457321.500000    6094720.000000
    3457247.500000    6094485.500000
    3457247.500000    6094485.500000
    3456976.250000    6094512.000000
    3456552.250000    6094553.500000
    3456552.250000    6094553.500000
    3456630.250000    6094656.000000
    3457078.250000    6095642.500000
    3457198.000000    6096357.500000
END
. 
.
.
END

The first line specifies the polygon ID and the label points. The following lines define the x and y coordinates (here in a Gauss Krueger projection) until the keyword END.
Thus, all informations needed for v.in.arc, i.e. the polygons, the label points and the label text, are collected in this file.

IN_ARC

The first program "in_arc.c" extracts these informations from the original file and creates the lines file, the label point file and the label text file. During this process, each polygon gets a unique ID, starting with 1. The correlation to the original ID is stored in the label text file.

PERMUT

Based on this data structure, the program "permut" scans the whole polygon file for identical nodes and removes these nodes by permutation of the data points. This is done in several iteration steps, until all identical nodes are removed. The program uses a temporary file, which will be copied after each iteration step to the original file. Thus after finishing the program, the original file contains the permutated polygons.

v.in.arc.poly

This shell script has been written to import the ARC/INFO data automatically into GRASS, using these two conversion programs. It will be called by:

	v.in.arc.poly ARC/INFO-file GRASS-vectorfile

First, this shell script runs in_arc to extract the lines, label point and label text information. It places the created files (*.ply, *.pnt, *.txt) into the /arc directory of the current mapset. Second, the program permut will be called, replacing the *.ply file created by in_arc. In the steps 3 and 4, the data will be imported using v.in.arc and v.support, resulting in the GRASS-vectorfile specified when calling v.in.arc.poly.

Last changed: $Date: 2002/01/25 05:45:35 $