Thanks very much for the clear explanation. As I wrote in my self-reply, and as you have highlitghted, I was mixing some concepts. I'm studying this because I will probably need to develop some routines for network analysis. I'm studying the graph structure right now...
Thanks again, Giovanni 2013/4/12 Markus Metz <[email protected]> > On Thu, Apr 11, 2013 at 11:32 AM, G. Allegri <[email protected]> wrote: > > 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) > > You would need to read the programmer's manual only if you want to > develop GRASS. The user manual should explain everything needed to use > GRASS. > > > 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 > > structures. > > > > - 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 point (GV_POINT) is not attached to nodes (in GRASS 7). P_line is an > internal structure that holds information about points, lines, > boundaries, centroids, faces. Or in your words, a structure P_line > does not hold information about nodes if it is of type GV_POINT. > > > 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? :( > > It seems you are mixing internal structures (P_line, P_node) and > feature types (GV_POINT, GV_LINE, GV_BOUNDARY, GV_CENTROID, GV_FACE). > In the example, there is one line (GV_LINE), and the end points of the > line are attached to nodes. Two end points -> two nodes, if the end > points are different. The "type = 2 (GV_LINE)" in the example for the > node refers to the feature type attached to the node. > > Markus M > > > > > I'm missing something. Could you help to understand it? > > Thanks a lot, > > giovanni > > > > > > [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 > > http://about.me/giovanniallegri > > blog: http://blog.spaziogis.it > > GEO+ geomatica in Italia http://bit.ly/GEOplus > > > > _______________________________________________ > > grass-user mailing list > > [email protected] > > http://lists.osgeo.org/mailman/listinfo/grass-user > > > -- Giovanni Allegri http://about.me/giovanniallegri blog: http://blog.spaziogis.it GEO+ geomatica in Italia http://bit.ly/GEOplus
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