A few remarks again below: On February 5, 2011 06:57:42 pm Ido Omer wrote: > Hi Elizabeth, > > Like in any interesting problem, we knew we will not be able to come up > with a general solution for all roads under any condition. We assume most > people are mapping asphalt/concrete roads and we decided to focus our > efforts there.
And even in that case, good luck! :-) See for example these two shots from Bing maps, Montreal, and how bad is the road extraction: http://tnorth.ch/blog/public/Dijkstra/tests/montreal1_out.jpg http://tnorth.ch/blog/public/Dijkstra/tests/montreal2_out.jpg (Showing, by the way, that a shortest-path algorithm is not always what we want to extract data in a robust way...) Image processing in that area is a pain: shadows, trees over the road, gray roofs that look pretty much like a road... > Eve there our solution is far from being perfect, but we > believe in most circumstances it has a value that is larger than zero. I don't really know what to think about that. The tool will maybe never be efficient to handle most cases, but can perhaps sometimes help, and it is a sufficient reason to try and improve it. Allowing the user to have some kind of control might help the detection to be done properly. > Strictly speaking, the current version doesn't look for road patterns; the > next version might do that and provide a more general solution. It will be > useful for us to learn what the community needs are; I'll be happy if you > could refer me to a few examples. In the mapping process (with JOSM or such tool), following roads is not really a problem, especially when they are not too sinuous (and that's when the road detector works well...). It can be done in a few clicks. Maybe the tool should try and act differently (but that is more GUI/UI related), and we could imagine the following scenario: - The user wants to map roads and selects a "road extraction" tool. - He roughly follows a road, maintaining a click (as you would do to paint with a brush in image processing softwares) - The algorithm knows the approximate path, and tries to fit exactly the center of the road. Regards, Thibault > BTW, by not using the detector its usefulness should be around zero, it is > hard for me to imagine how can it drop much lower than that (at least for > the long run, after you wasted a couple of minutes and found out it does > not serve your needs) > > Thanks, > Ido > > -----Original Message----- > From: Elizabeth Dodd [mailto:[email protected]] > Sent: Saturday, February 05, 2011 2:27 PM > To: [email protected] > Subject: Re: [OSM-talk] (magical?) road detector > > I've made one attempt only at tracing a dirt road in dry country with the > detector. I found its usefulness less than zero, as the system told me > that too many tiles were involved and quit. Zooming in is not always > practical to spot these roads, where the pattern recognition is a very > long straight feature on a photograph, and same colour as the surrounds > for a dirt road in dry country, and a dark colour for a railway. Having > spotted the road then it is easier to find in zoomed images when looking > for curved bits through (dry) waterways. I went back to doing it by hand, > so for me it had a uselessness of less than zero. > > _______________________________________________ > talk mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/talk > > > _______________________________________________ > talk mailing list > [email protected] > http://lists.openstreetmap.org/listinfo/talk _______________________________________________ talk mailing list [email protected] http://lists.openstreetmap.org/listinfo/talk
