> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:geotools-devel- > [EMAIL PROTECTED] On Behalf Of Matthias Basler > Sent: Thursday, October 06, 2005 3:59 PM > To: Luca Sigfrido Percich > Cc: geotools-devel@lists.sourceforge.net > Subject: Re: [Geotools-devel] Re: Proposals: Topology > > Zitat von Luca Sigfrido Percich <[EMAIL PROTECTED]>: > > I think that topology cannot be simply geometry-based, it needs a > > Feature model to work with, so that features can be related to each > > other in a persistent way based on attributes. > > Cannot follow here. Sorry. > Probably it's me not understanding some important point of it, but when I > thing > about geometry, topology and features I see following schema: > > - Geometry cares about describing the ... well ... geometry (in > mathematical > sense) of a feature > - There are validation rules that might apply to check, if, f.e. > geometries are > allowed to overlap etc. > - Features hold the (or some) geomtry/-ies and attributes. When I think > about > attributes I have the "usual" attribute table in mind, which means that I > speak > of "user-defined" attributes, attributes that the user somehow attached to > the > geometries - nothing "geotools internal". > > Now, a topology whould combine the geometry (in mathematical sense) and > some > special rules into topological objects that would take care about > validation > and what is possible, without Features and attributes and such getting > involved > primarily. > Features would work as above.
Yes, I agree. When we are talking about topology, we take into account geometry. When in my previous post I talked about "abstraction" from data model, I meant that data model is geometry-based: we should able to build TDM from list of geometries, or from list of features with geometry or from something else.. (it is a just adaptation any geometry-based models for TDM building while actual geometry can be internal in data model (as an geometric attribute of feature, for example)). > In my understanding the (spatial?) "relation" of features to each other is > managed in one central object (the "topology"?), which could maybe become > incorporated into a FeatureCollection? A topology in the mathematical > sense is > just a collection of nodes, edges and faces, i.e. features (Just thinking > loud.) While topology is based on spatial relations, arbitrary non-geometric objects might be bound to TDM. In that sense we are talking about features, for example. In TDM we have FACE object, so arbitrary objects can be bound to FACE (one or more features whose geometry is inside of the FACE, whatsoever). As a result, we have initial data, feature model for example (Why can we use feature model - just because each feature has a geometry - it is the only one thing that makes sense for topology). We build TDM (that consists from NODE, EDGE, FACE,...) and bind different additional attributes/objects/entities to TDM entities. Example: polygonal coverage (no overlapping, just touches of boundaries) -> TDM that is based on common boundaries of polygons -> each FACE has a polygon (or feature with polygon as a geometry) attached to it. This illustrates what I'm talking about. TDM may have different semantic sense. It can facilitate navigation purposes, topological quering (find all houses that are on the right side of the road), or editing operations of vector data in desktop GIS application... If we design good object model, it can serve everywhere.. I believe :) > > > So if JTS has to provide a topology model, I think there might be two > > possible solutions: ... > > My idea was simply that JTS provides the geometrical part of it (the > "topology" > and the topology primitives node, edge, face), and GeoTools would extend > the primitives (or wrap them or whatever) to Features, i.e. add/manage > attributes and all the other needed stuff. I agree with Mattias. This what you are talking about, I call "binding" in this message. Is it impemented as an association , or aggregation, (in OOP terms) or... it is just an issue to be solved by common forces. Geometry makes sense for topology. > > .. Guess I am looking at it from a much too simple point of view. :-( > > Matthias Basler > [EMAIL PROTECTED] > > ---------------------------------------------------------------- > This mail was sent through http://webmail.uni-jena.de > > > ------------------------------------------------------- > This SF.Net email is sponsored by: > Power Architecture Resource Center: Free content, downloads, discussions, > and more. http://solutions.newsforge.com/ibmarch.tmpl > _______________________________________________ > Geotools-devel mailing list > Geotools-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/geotools-devel ------------------------------------------------------- This SF.Net email is sponsored by: Power Architecture Resource Center: Free content, downloads, discussions, and more. http://solutions.newsforge.com/ibmarch.tmpl _______________________________________________ Geotools-devel mailing list Geotools-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/geotools-devel
