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 > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
