Geography Reference
In-Depth Information
requires something with geoprocessing capability. In this case, Harri-
son could have converted his digitized lakes (which likely began life as
a shapefile) into a PostGIS or GRASS layer. Both of these give him the
functionality he needs to create a buffer. In the case of PostGIS, it's
done with a fairly simple SQL query. In GRASS, he can use the v.buffer
command or the buffer module in the QGIS-GRASS toolbox.
PostGIS is a good example of a reason to convert. Not only does it
improve data management by giving you a “portal” to your data, but it
has been certified as OGC compliant and provides the spatial functions
specified in the Simple Features Specification for SQL. This means that
When software is
certified as OGC
compliant, you can be
assured that it adheres
to established standards
and can interoperate
with other compliant
software.
not only can we display and edit PostGIS data in an application-like
QGIS, we also get a whole batch of spatial functions that we can use
to query the relationships between features, transform between pro-
jections, and create new features. If you find that your work requires
more than just simple viewing and editing, then conversion is worth
considering.
Enhanced GIS Capabilities
The other reason to convert is to gain enhanced GIS functionality.
You're probably asking what the difference is between this and the
improved functionality aspect we just covered. You can view it as a
progression to more powerful and perhaps complex GIS operations.
We're pretty much talking about GRASS and its bountiful assortment of
vector- and raster-processing tools. Since GRASS stores data in its own
format, we need to convert our existing data in order to take advantage
of the tools.
Examples of the type of capabilities we're talking about include the
following:
• Line-of-sight analysis
• Union and intersection of layers to create a new layer
• Merging raster data
• Mathematical operations on grids
• Contouring
We'll dive into some of these topics later in Chapter 10 , Geoprocessing,
on page 149 .
 
 
Search WWH ::




Custom Search