Hi Rob, thanks for your reply. > I've yet to see many robust implementations of visibility analysis -I > used to use this as the case study for how to lie with GIS when I > lectured on the subject. > > variability within the limits of precision of DEMS (or whatever else you > use to map the terrain) cause huge error margins in the computed > visibility. Any accuracy issues (actual errors outside the limits of > precision) are disastrous.. > > I saw one example using Monte Carlo techniques (to introduce repeated > random changes within the limits of precision) that concluded that the > actual viewshed cannot be measured to within about 50% of the real > value. I.e. if you think you have 100 ha of viewshed, it may be 50 or 200!
I was thinking about that also. I talked to people that want to do analysis using srtm 90 m dems. I uderstand your issues. > Still, it makes pretty pictures to please politicians I suppose, but > please be careful about implementing a poor aproach (i.e. if the inbuilt > tools created a min and max and average position for a line of sight, > this would promote better analysis, and make the tool more important. I > dont know how hard this is to achieve for an entire viewshed - suspect > the algorithms would be quite tricky, but for a single line of sight its > pretty simple. I would not want to implement a thing from scratch. I know GRASS has a los analysis tool, but I couldn't find one that does it simply between two points. So my question was more about: is there something in geotools already that does something similar, since I would like to port such a tool into udig? However, if you make some accurate tests, you probably can give me an advice about GRASS's module? I was considering to look into the code to link it to udig. At that point I'm not sure if I'm not getting OT... Sorry Andrea > > Rob > > Andrea Antonello wrote: >> Hi developers, >> is there some class that does line of sight (visibility analysis) taking >> into consideration the earth curvature? >> I think I saw something, but I can't find it any more. >> >> Thanks, >> Andrea >> >> ------------------------------------------------------------------------- >> This SF.net email is sponsored by DB2 Express >> Download DB2 Express C - the FREE version of DB2 express and take >> control of your XML. No limits. Just data. Click to get it now. >> http://sourceforge.net/powerbar/db2/ >> _______________________________________________ >> Geotools-devel mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/geotools-devel >> > ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Geotools-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
