[GRASS-user] confused by the GRASS Programmer's topology examples...

G. Allegri giohappy at gmail.com
Thu Apr 11 02:32:07 PDT 2013

Hi all,
I'm reading the GRASS7 programmer's manual, to update my experience with
GRASS (I'm going to use it for some network analysis, and probably I will
need to extend it)
Looking at the topology examples [1] I fill a bit confused by the "types"
of nodes and lines, which vary between the different kind of topological

 - Point example: a point doesn't have nodes but have a line (P_LINE), with
type GV_POINT.
It's enough for me to get confused :)
A P_LINE structure has a void * topo opaque element [2], which will point
to the relative topology structure depending on the type. In case of a
G_POINT type, what is the topology structure attached to the topo pointer?

 - Line example: two nodes with type GV_LINE. A P_NODE doesn't have a type
[3], so how can it be... a GV_LINE? :(

I'm missing something. Could you help to understand it?
Thanks a lot,

[1] http://grass.osgeo.org/programming7/vlibTopology.html#vlibTopoExamples
[2] http://grass.osgeo.org/programming7/structP__line.html
[3] http://grass.osgeo.org/programming7/structP__node.html

Giovanni Allegri
blog: http://blog.spaziogis.it
GEO+ geomatica in Italia http://bit.ly/GEOplus
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