View source for 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 [http://data.neteler.org/geostat2012/north_carolina here]

===Importing Vector data===
The GRASS modules <code>v.in.*</code> and <code>v.out.*</code> handle the importing and exporting of Vector datasets. 
<code>v.in.ogr</code> is widely used and has simplified the import of vector data; [http://www.gdal.org/ogr/ogr_formats.html OGR] itself support a wide range of formats.
<code>v.out.ogr</code> always exports the entire vector map

====Importing an ESRI Shapefile====
The following code snippet is a simple usage of <code>v.in.ogr</code>, which imports an ESRI Shapefile into the native vector format:

 v.in.ogr dsn=boundary_county.shp out=boundary_county 

However, <code>v.in.ogr</code> 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:

[[File:Vector_layer_manager.png|400px]]
[[File:Vector_layer_import.png|400px]]

You can easily import a '''subset''' of your data by specifying the spatial extent or an SQL query defined within the <code>where</code> 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 <code>v.external</code>

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 <code>v.in.ascii</code> 
 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 replicate the above procedure for three dimensional data (XYZ), by modifying the <code>v.in.ascii</code> 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 <code><b>v.in.dxf</b></code>. 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

[[File:import_dxf.png|400px]]

And then visualised within the map display

[[File:dxf_display.png|400px]]

===Exporting Vector data===

Using the module <code>v.out.ogr</code> 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,

[[File:Vector_out_ogr.png|400px]]
[[File:Vector_layer_export.png|400px]]


Introductory information on [http://grass.ibiblio.org/grass63/manuals/html63_user/vectorintro.html 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