Zitat von Luca Sigfrido Percich <[EMAIL PROTECTED]>: > I understand. I also understand that probably you have a more > "mathematical" approach to topology, while I'm mostly focused on > topology application to geographic databases. Moreover, my personal > view of GIS is trongly "database oriented", so to me geometry is > nothing more than an attribute like name, address, road type and so > on. > > Sure the two approaches are not "incompatible" but need to be somehow > "resized" and placed correctly one near the other so we can plan a > good API for topology.
Yup. And after your explainations I can better see your way of reasoning. > BTW: I don't like CAD because CAD is still extensively used for > preparing maps... and people using CAD usually is still focused on > "drawing" rather than on data and database design. ;o) Just as a side note: Just visited a geonformatics/geodesy fair in Duesseldorf, Germany. CAD was one big topic, and it is definitely putting a foot in the door towards GIS, especially where 3D GIS models are needed. Backside is that its metadata handling is still limited. So the proposed solution seems usually "CAD for modelling the geometries, GIS for putting them in their context". > Maybe it's not needed at the geometric level. But think of > application tasks like "select all the borderlines that separate > polygons of type A from polygons of type B" Sure. For such tasks you need actual feature relationships. > Yes, but in a GIS I usually don't need *just* the coordinates of the > start point - I need the *Junction Feature* - which has a point > geometry located at the start (or end) point of the geometry of a > RoadElement (and this is the implicit relationship) - and I need the > Feature because the Junction has related info on vehicle manoveurs, > traffic light regulation and so on... I see. Quick question: Can one geometry be reused in multiple features? If not, the geometry could simply hold a back reference to it's parent feature. > Oh, yes, that's what I wanted to ask you: let's say you deal with > geometries only. Do you expect to use IDs for geometries? Or do the > geometries relate to each other simply by reference (I mean Java > object variables or pointers). Nice question. Of course I ran into this already. My first idea was to use IDs, because that is what you usually learn when you learn how topology works. So I added IDs to my draft topology geometries. But then I realized that Java actually does this "ID"ing internally, and I could just reference the geometries directly. (But of course this works only when you are not streaming the geometries/features from a remote place on demand, but have the whole geometry collection available at any time.) So my attitude is: I find direct references more intuitive and quicker, but there might be constraints (like streaming) that might make the ID approach unavoidable. However IDs always need an explicite "lookup" mechanism, be it a simple Hashmap or something more sophisticated. I have no experience how much this slows down things like drawing in large datasets. What's your opinion and experience on that? > I don't like the idea of using 3D, mostly 'cause I'm a flat-minded > dinosaur. :o))) It's a step forward "cartography", i.e. 2D > representation... and sure in future mapping apps, especially in > urban situation, it will be more and more important. It is already! Half the companies on the mentioned fair had something to do with 3D: Laser scanners, photogrammetry, tachymetry, city models, 3D visualization all around. > For now I'd rather stick on 2D models. Yes, this has priority. But I like to care that the API will have some point(s) where a future 3D API could hook in/extend it. Shouln't be a big problem. > I started the Topology wiki at > > http://docs.codehaus.org/display/GEOTOOLS/Topology+Framework > > and added a page with use cases from my work on road networks (just a > skeleton, I still have to write down everything, I hope during the > weekend). Good. I'll add my wishes and ideas there as soon as the page takes shape a bit. Thanks for this interesting discussion. 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 [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
