GRASS GIS 7 Programmer's Manual  7.5.svn(2018)-r72892
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Vector ASCII Format

by GRASS Development Team (http://grass.osgeo.org)

Vector ASCII Format Specifications

The GRASS ASCII vector map format may contain a mix of primitives including points, lines, boundaries, centroids, faces, and kernels. The format may also contain a header with various metadata (see example below).

Vector map can be converted to the ASCII representation at user level by v.out.ascii format=standard command.

See Vector ASCII functions for list of related functions.

The header is similar as the head file of vector binary format (see Header file format specification) but contains bounding box also. Keywords are:

ORGANIZATION
DIGIT DATE
DIGIT NAME
MAP NAME
MAP DATE
MAP SCALE
OTHER INFO
ZONE
WEST EDGE
EAST EDGE
SOUTH EDGE
NORTH EDGE
MAP THRESH

Example:

ORGANIZATION: NC OneMap
DIGIT DATE:   
DIGIT NAME:   helena
MAP NAME:     North Carolina selected bridges (points map)
MAP DATE:     Mon Nov  6 15:32:39 2006
MAP SCALE:    1
OTHER INFO:   
ZONE:         0
MAP THRESH:   0.000000

The body begins with the row:

VERTI:

followed by records of primitives:

TYPE NUMBER_OF_COORDINATES [NUMBER_OF_CATEGORIES]
 X Y [Z]
....
 X Y [Z]
[ LAYER CATEGORY]
....
[ LAYER CATEGORY]

Everything above in [] is optional.

The primitive codes are as follows:

  • 'P': point
  • 'L': line
  • 'B': boundary
  • 'C': centroid
  • 'F': face (3D boundary)
  • 'K': kernel (3D centroid)
  • 'A': area (boundary) - better use 'B'; kept only for backward compatibility

The coordinates are listed following the initial line containing the primitive code, the total number of vectors in the series, and (optionally) the number of categories (1 for a single layer, higher for multiple layers). Below that 1 or several lines follow to indicate the layer number and the category number (ID).

The order of coordinates is

  X Y [Z]

Note: The points are stored as y, x (i.e., east, north), which is the reserve of the way GRASS usually represents geographic coordinates.

Example:

P  1 1
 375171.4992779 317756.72097616
 1     1 
B  5
 637740       219580      
 639530       219580      
 639530       221230      
 637740       221230      
 637740       219580      
C  1 1
 638635       220405      
 1     2

In this example, the first vector feature is a point with category number 1. The second vector feature is a boundary composed by 5 points. The third feature is a centroid with category number 2. The boundary and the centroid form an area with category number 2. All vector feature mentioned above are located in layer 1.