GRASS Vector Layers

Introduction

Grass documentation provides basic information about vector attribute management. categories of vector features and vector layers.

The aim of this tutorial is to show how to create, manipulate and display different layers of a vector using relational database.

Problem Description

An organization provides information about routes to be driven by drivers. The organization's database consists of

• roads (road network)
• routes driven on that roads

Simple approach can be taken to present the routes to drivers. For every route a vector map could be created and overlayed over the road network vector, i.e.

   $ d.vect map=roads
   $ d.vect map=route01 color=green width=2

Above idea has a major flaw. If route data changes or new route is added then vector maps has to be regenerated or removed.

Assuming that route network and routes data are stored in relational database, the database tables can be linked to road network map as its layers. Such layer information could be utilized to display maps, i.e.

   $ d.vect map=roads
   $ d.vect map=roads layer=2 where="route_id=1" color=green width=2

The tutorial reuses road network provided with Spearfish data. To solve problem defined above, the roads data and sample routes needs to be prepared. This is described in next section.

Prepare Road Network

create table road_network (cat integer, id integer);

v.category --o in=roads out=outmap option=del

v.category --o in=outmap out=stepmap option=add

v.to.db map=setpmap option=cat

update road_network set id=cat;

http://grass.osgeo.org/grass63/manuals/html63_user/vectorintro.html