vectorascii.1grass - Man Page
GRASS ASCII vector format specification
A vector map in GRASS native vector format may contain a mix of primitives including points, lines, boundaries, centroids, areas, faces, and kernels. The GRASS ASCII vector format may contain also a header with various metadata (see example below).
The header is similar as the head file of vector binary format but contains bounding box also. Key words 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
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 [Â ] 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 coordinates 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]
In pre-GRASS 6 versions of the ASCII format, the order of coordinates was different:
Y X
Latitude/Longitude data may be given in a number of ways. Decimal degrees must be positive or negative instead of using a hemisphere letter. Mixed coordinates must use a hemisphere letter. Whole minutes and seconds must always contain two digits (example: use 167:03:04.567; and not 167:3:4.567).
Acceptable formats:
key: D=Degrees; M=Minutes; S=Seconds; h=Hemisphere (N,S,E,W)
- (+/-)DDD.DDDDD
- DDDh
- DDD:MMh
- DDD:MM.MMMMMh
- DDD:MM:SSh
- DDD:MM:SS.SSSSSh
Examples
ORGANIZATION: GRASS Development Team DIGIT DATE: 1/9/2005 DIGIT NAME: - MAP NAME: test MAP DATE: 2005 MAP SCALE: 10000 OTHER INFO: Test polygons ZONE: 0 MAP THRESH: 0.500000 VERTI: B 6 5958812.48844435 3400828.84221011 5958957.29887089 3400877.11235229 5959021.65906046 3400930.7458436 5959048.47580612 3400973.65263665 5959069.92920264 3401032.64947709 5958812.48844435 3400828.84221011 C 1 1 5958952.42189184 3400918.23126419 1 20 B 4 5959010.9323622 3401338.36037757 5959096.7459483 3401370.54047235 5959091.38259917 3401450.99070932 5959010.9323622 3401338.36037757 C 1 1 5959063.08352122 3401386.98533277 1 21
In this case the vector map contains 2 boundaries (first boundary with 6 vertices, second with 4 vertices) without category and 2 centroids with category number 20 and 21 (layer 1).
See Also
v.in.ascii, v.out.ascii, v.edit
Source Code
Available at: GRASS ASCII vector format specification source code (history)
Accessed: Saturday Jul 27 11:27:22 2024
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