GRASS GIS 7 Programmer's Manual  7.5.svn(2018)-r73120
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GRASS-OGR data provider

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

Pseudo-topology

Reduced topology: each boundary is attached to one area only, i.e. smoothing, simplification, removing small areas etc. will not work properly for adjacent areas or areas within areas.

Full topology is only available for native GRASS vectors or can only be built after all polygons are converted to areas and cleaned as done by v.in.ogr.

Frmt file format specification

Frmt is a plain text file which contains basic information about external format of linked vector map. Each line contains key, value pairs separated by comma.

OGR specific format is described by:

  • FORMAT - ogr
  • DSN - OGR datasource name
  • LAYER - OGR layer name

Example:

FORMAT: ogr
DSN: /path/to/shapefiles
LAYER: cities

OGR layer can be linked via v.external command. When linking OGR layer pseudo-topology ('topo') is built including spatial index file ('sidx') and category index file ('cidx'). Additionally also feature index file (see Fidx file format specification) is created.

Fidx file format specification

Note: finfo is an instance of Format_info structure.

NameTypeNumber

Description

Version_Major C1file version (major)
Version_Minor C1file version (minor)
Back_MajorC1supported from GRASS version (major)
Back_MinorC1

supported from GRASS version (minor)

byte_orderC1

little or big endian flag; files are written in machine native order but files in both little and big endian order may be readl; zero for little endian

lengthL1

header size

fInfo.ogr.offset_numI1

number of records

fInfo.ogr.offsetIoffset_num

offsets