[Gvsig_english] Different results from buffering using SEXTANTE & Geoprocessing tools OADE

[Dr. F. Patrick Graz]

Hi all,
I'm using gvSIG to teach an introduction to GIS. During a practical
exercise, however, I found that buffering in the geoprocessing tools and in
SEXTANTE produce different results. Using line (a road data set) data to
buffer -

- the geoprocessing tools permit the merging of buffer zones into 1. If this
option is not set, however, the resulting buffer file contains line
features, not polygons. In this instance the attributes of the lines are
attached to the output, but no buffer distance is specified.
- With 'merging' enabled, the output is a polygon file, and shows the buffer
distance.
- buffering concentric zones without merging produced the line features
indicated earlier
- buffering concentric zones with merging of features caused the merging of
all zones into one.

- buffering in SEXTANTE does not provide the option of merging. However, the
attributes of the output show both the attributes of the lines as well as
the buffer distance.
- when manually dissolving this output using SEXTANTE, however, the
intersections of lines were surrounded by a 'roundabout'/traffic circle.

:-) the students were able to complete their project, but there was a little
consternation on the side.

Has anyone observed similar issues?

Patrick

------------------------------------------
Dr. F. Patrick Graz
Snr. Researcher, 
Multidisciplinary Research Centre, 
University of Namibia