GRASS 6 Tutorial/Vector data management
Vector data management
Overview
The native GRASS vector format provides:
- Vector topology
- m:n mapping of geometry features to attributes
- Vector layers
- OGC Simple Features <-> Topological Vector Conversion
- Database Management system (DBMS)
- SQLite, PostgreSQL + PostGIS, MySQL, ODBC (, DBF)
The vector geometry types supported in GRASS includes:
- Point
- Centroid
- Line
- Boundary
- Area (Boundaries + Centroid)
- Face (3D Area)
- [Kernel (3D Centroid)]
- [Volumes (Faces + Kernel)]
All types are true 3D: x,y,z
The examples that follow in this section on vector data management are based on the datasets available here
Importing Vector data
The GRASS modules v.in.* and v.out.* handle the importing and exporting of Vector datasets.
v.in.ogr is widely used and has simplified the import of vector data; OGR itself support a wide range of formats.
v.out.ogr always exports the entire vector map
Importing an ESRI Shapefile
The following code snippet is a simple usage of v.in.ogr, which imports an ESRI Shapefile into the native vector format:
v.in.ogr dsn=boundary_county.shp out=boundary_county
However, v.in.ogr has many options to import subsets (defined spatially or by SQL) and vector types
The same can be achieved using the GRASS Graphical Interface. The Vector import interface can be accessed through the vector layer manager:
You can easily import a subset of your data by specifying the spatial extent or an SQL query defined within the where command line argument:
v.in.ogr --o dsn=./ output=subset layer=boundary_county where="NAME = 'DUPLIN' OR NAME = 'WAKE'"
+----------------------------------------------------------------------------+ | Layer: subset | | Mapset: PERMANENT | | Location: nc_spm_08_geostat | | Database: /home/daniel/GRASSWiki/data | | Title: | | Map scale: 1:1 | | Map format: native | | Name of creator: daniel | | Organization: | | Source date: Wed Nov 7 16:10:01 2012 | |----------------------------------------------------------------------------| | Type of Map: vector (level: 2) | | | | Number of points: 0 Number of areas: 2 | | Number of lines: 0 Number of islands: 2 | | Number of boundaries: 2 Number of faces: 0 | | Number of centroids: 2 Number of kernels: 0 | | | | Map is 3D: No | | Number of dblinks: 1 | | | | Projection: Lambert Conformal Conic | | N: 258121.97732598 S: 106860.16001618 | | E: 732841.78315847 W: 610047.98051883 | | | | Digitization threshold: 0 | | Comments: | | | +----------------------------------------------------------------------------+
Virtual link an ESRI Shapefile
If you prefer not to import your vector datasets into the native GRASS vector format, you can create a virtual link to it using v.external
This can be done as follows:
v.external dsn=./ output=boundary_county layer=boundary_county Building topology for vector map <boundary_county>... Number of nodes: 1707 Number of primitives: 1981 Number of points: 0 Number of lines: 0 Number of boundaries: 1055 Number of centroids: 926 Number of areas: 1055 Number of isles: 1055 Number of areas without centroid: 129
Import an XY/XYZ ASCII file
You can easily generate a GRASS point vector file from a text file containing X,Y coordinates.
642934|95324 675695|139878 623277|158224 716318|138568 742527|164776 735975|196227 755631|200158
Pipe the coordinates to the module v.in.ascii
cat coords.txt | v.in.ascii out=points
Add the categories to the vector points to facilitate attribute joins:
v.category in=points out=points_final op=add v.category points_final op=report
You can then add a new attribute table to the vector file using v.db.addtable
v.db.addtable map=points
You can replicate the above procedure for three dimensional data (XYZ), by modifying the v.in.ascii argument list
You can easily generate a GRASS point vector file from a text file containing X,Y coordinates.
642934|95324|212 675695|139878|233 623277|158224|211 716318|138568|219 742527|164776|240 735975|196227|221 755631|200158|210
cat coords.txt | v.in.ascii -z out=points
Importing a DXF file
Both 2D and 3D DXF files can be imported into GRASS using the module v.in.dxf. This can be done very simply from the command-line as follows
v.in.dxf -1 Masterplanxy.dxf
100% Following DXF layers found: Layer 1: line Building topology for vector map <Masterplanxy>... Registering primitives... 64302 primitives registered 405521 vertices registered Building areas... 100% 0 areas built 0 isles built Attaching islands... Attaching centroids... 100% Number of nodes: 71142 Number of primitives: 64302 Number of points: 0 Number of lines: 64302 Number of boundaries: 0 Number of centroids: 0 Number of areas: 0 Number of isles: 0
This can also be done using the GUI interface
And then visualised within the map display
Exporting Vector data
Using the module v.out.ogr it is possible to export native GRASS Vector data to a range of formats:
ESRI_Shapefile,MapInfo_File,TIGER,S57,DGN,Memory,BNA,CSV,GML,GPX,KML,GeoJSON,GMT,SQLite,ODBC,MSSQLSpatial, PostgreSQL,MySQL,PCIDSK,DXF,Geoconcept,GeoRSS,GPSTrackMaker,PGDump,GPSBabel,
Introductory information on vector data processing is available from the help manual.
Grass Six Tutorial Default Settings
- Default settings for vector geometry;
for vector attributes; for db.* modules
Grass Six Tutorial Geometry Management
http://grass.osgeo.org/grass57/tutorial/geom_storage.html
- General notes on Geometry
management; Managing the default settings;
GRASS vector architecture; Geometry stored in native format;
Geometry stored in SHAPE file;
Import/export of vector data Geometry;
Generating vector geometry from various sources
Grass Six Tutorial Attribute Management
http://grass.osgeo.org/grass57/tutorial/attrib_storage.html
- General notes on Attribute
management; Managing the default settings; Examples;
Database Schema