Re: [Talk-GB] building shapes from OS Street View
From: Robert Scott li...@humanleg.org.uk That's great! I can stop reading about Harris operators. I totally agree about orthogonal snapping. Orthogonal snapping would be useful more generally - do any of the editors have this feature for manually drawn buildings etc.? -- Steve ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] building shapes from OS Street View
On Sat, Apr 10, 2010 at 9:23 AM, Steve Doerr steve.do...@blueyonder.co.uk wrote: Orthogonal snapping would be useful more generally - do any of the editors have this feature for manually drawn buildings etc.? JOSM has an Orthogonalise shape option which is very useful for buildings. Glenn. ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] OS StreetView accuracy: caution!
On Fri, Apr 9, 2010 at 7:00 PM, Kevin Peat ke...@kevinpeat.com wrote: On 9 April 2010 18:40, Robert Scott li...@humanleg.org.uk wrote: Hasn't one of OSM's (many) mantras been doesn't matter if it's approximate: someone can always improve it later or rough is better than nothing? Sure, some of the OS data is rough, but it is better than nothing, and quite good for a first pass. +1 on this. It seems odd to me that we are encouraging people to contribute using often pretty rubbish mobile phone gps receivers but complaining that the OS data is not sub-metre accurate. I think the point is not to assume that where OSSV and OSM disagree, that OSSV is necessarily the correct one. It might generally be, but if you can't go out and check, be very careful what you do. If it's just how curvy it is I generally find checking the OSM GPS traces is a good idea, because you often find the GPS trace just hasn't been followed very well. Maybe some people will be put off if the empty areas are filled in with OS data so they don't have a blank canvas but I bet there are just as many people out there not knowing where to start who would add street names and POIs and clean-up any OS errors. That's a very good summary. By far the most important thing is not to leave a mess. Dave ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] Separation of sources
Simon Ward si...@... writes: I’d just like to see something where ground surveyed data is the ultimate, and it’s not clear to me that it is the ultimate now. I've done a fair bit of ground surveying, but all of it has been from the starting point of an existing map - usually one traced from the aerial imagery. If the street layout appears slightly wrong I won't usually correct it, because the GPS precision is not good enough in heavily built-up areas. (Only if there is an obvious tracing mistake or a missing street will I use the GPS data to make changes to geometry.) So what we have at the moment, in the UK at least, is already a mishmash of photographs, ground survey, and (in rural areas) tracing from older OS maps. A pure survey-only OSM has not existed except in the very early days before Yahoo photos. If what you mean is that in the event of a disagreement, the only way to check map data is to look on the ground, then of course this has always been true. I don't think importing from any other source changes that. Do remember that the OS maps have also been produced largely by ground survey, and their surveyors are no less skilled or dedicated than our OSM volunteers. -- Ed Avis e...@waniasset.com ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] building shapes from OS Street View
It's worth noting that the Yahoo aerial photography is also out of date; in some cases [1] people have traced streets from the photo which bear no relation to what's on the ground. Yet nobody suggests we should stop tracing from it. Yes they do. http://lists.openstreetmap.org/pipermail/talk/2007-September/017830.html I've slightly changed my mind since then, but anyway. Dave ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] building shapes from OS Street View
Glenn wrote: JOSM has an Orthogonalise shape option which is very useful for buildings. And a terracer plugin which I find useful for converting traced buildings to semi-detached* (or however many) properties. Ed * Slight issue when the width of the two semi-detached houses together is less than their depth as it then splits the rectangle on the wrong axis, but this seems fairly rare around here (and I now know how to rotate objects in JOSM as a result). ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
[Talk-GB] building shapes from OS Street View
Hi again, thanks for the comments. How well would this scale up to the whole country? (!! Not automatically importing the results of course !!) I'm thinking about tile/batch sizes, tile boundary issues, I was thinking about using a sliding window approach, by loading in an extra margin from surrounding tiles, selection pixels by colour, create edge fragments as before. But in this case, the step that creating polygons should only use the central region of the image for the starting point of the polygon. This should avoid any buildings getting cut in half at the tile edge. any necessity for porting parts to c++ for speed etc. Converting edge fragments to polygons is the slow step at the moment - about 15 minutes a tile. I am using the approach describe in the link below. Fortunately, I know a bit of Boost.Python and C++ if we need the speed. I suspect a better algorithm in python could improve the speed issue rather than resorting to C++. http://losingfight.com/blog/2007/08/28/how-to-implement-a-magic-wand-tool/ I am also seeing the limitations of my approach. Problems arise from the lack of image resolution and the anti-aliasing of the colours in the image. Since I am using a binary classification by colour for selecting pixels, it tends to result in rounded corners (due to the colour blending into the backgound). The polygon simplification then has to descriminate between a rounded corner due to anti-aliasing and corner which is real. Given the resolution, a straight edge might only be 2 or 3 pixels long, and a rounded corner has a radius of about... 2 or 3 pixels. But then, these building shapes are also a total nightmare to manually survey. Example attached (you will probably need to zoom in): http://timsc.dev.openstreetmap.org/dev/hard-building-shapes.png I have some ideas for a better algorithm (based on active contour models), but that is pretty complex. I will give that some thought. Basically, we need to segment the shape but not by simply binary selecting pixels inside or outside the shape (and it can try to be orthogonal, if possible). The code I have does provide a good initialisation of the model, so it is hardly wasted effort. If anyone has any better ideas, you can have a copy of my python code to try things. Regards, TimSC ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] building shapes from OS Street View
On Saturday 10 April 2010, TimSC wrote: Converting edge fragments to polygons is the slow step at the moment - about 15 minutes a tile. I am using the approach describe in the link below. Fortunately, I know a bit of Boost.Python and C++ if we need the speed. I suspect a better algorithm in python could improve the speed issue rather than resorting to C++. If needs be, and other algorithms fall short, the advantages c++ has are things like ability to optimize for cache behaviour, ability to choose algorithms for your data structures (such as lists) which I imagine are getting hammered by your approach. A last resort though. http://losingfight.com/blog/2007/08/28/how-to-implement-a-magic-wand-tool/ I am also seeing the limitations of my approach. Problems arise from the lack of image resolution and the anti-aliasing of the colours in the image. Since I am using a binary classification by colour for selecting pixels, it tends to result in rounded corners (due to the colour blending into the backgound). The polygon simplification then has to descriminate between a rounded corner due to anti-aliasing and corner which is real. Given the resolution, a straight edge might only be 2 or 3 pixels long, and a rounded corner has a radius of about... 2 or 3 pixels. But then, these building shapes are also a total nightmare to manually survey. Example attached (you will probably need to zoom in): Indeed. The approach I was going to take was taking the buildings as anti-aliased grayscale ( which I guess I would have to be generated by tuning a few heuristics about which indexed colours to pick ) and use a corner finding algorithm on them. I was hoping to be able to get sub-pixel accuracy with this approach (corner detectors are perfectly capable of it with grayscale data), but I still have a few papers to read. I was thinking momentarily of a hybrid approach, using detected corners to more precisely position nodes. As far as the orthogonalizer idea goes, I think a simple refinement would need to be made - orthogonalization threshold would need to be inversely proportional to segment lengths. Lengths that are short relative to pixel size will have more quantization errors than long segments. I have some ideas for a better algorithm (based on active contour models), but that is pretty complex. I will give that some thought. Basically, we need to segment the shape but not by simply binary selecting pixels inside or outside the shape (and it can try to be orthogonal, if possible). The code I have does provide a good initialisation of the model, so it is hardly wasted effort. If anyone has any better ideas, you can have a copy of my python code to try things. You've done a lot better than me - I'm still at the 'reading papers' stage ;) robert. ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] Nonsense edits in Durham London - revert required
Well spotted ddixon, some of those edits seem like clear he he, you can change wikipedia to say what you like edits. There have just been some accidental deletes in Canada and it seems like the way to deal with them is manually. To undelete a way, press u, wait 5–10 seconds for the deleted ways to load, select the way to undelete, and press k. To revert a way to an earlier version, select the feature, press k, choose the version, and click Revert. From the Potlatch documentation: * undelete will always use the most recent version of each constituent node (even if it's moved) * revert will use the historic version of each constituent node, but if that node is still visible and has moved somewhere else, it will generate a new node ID My mouse is far to sensitive in clicking (I think I need to clean it) to deal with Potlatch easily. Can you manage to put everything back? Please post the mailing list how the users respond. If there is no response and there are more edits (or your corrections get put back) then a block is likely needed, which can be done through OSM Foundation people (or at least they know who does it). Hopefully once the stuff is put back then the users will either contribute responsibly or move on to troll elsewhere. On 7 April 2010 10:54, David Dixon da...@ddixon.force9.co.uk wrote: User Ajbites has made a number of obviously nonsensical edits this afternoon, mainly in Durham but also 1 in Haiti and 1 in London. I have sent a polite welcome, but please don't email. Could someone with the required knowledge please revert these edits? One slight complication is that another very new user (bashiboy2) has already re-edited some of these ways. These edits appear mainly neutral but the closeness in timing suggests the two users are connected - there doesn't appear to be any new useful data here either so if necessary these edits can be reverted too. Thank you, David Ajbites: http://www.openstreetmap.org/browse/changeset/4354930 http://www.openstreetmap.org/browse/changeset/4354906 http://www.openstreetmap.org/browse/changeset/4354900 http://www.openstreetmap.org/browse/changeset/4354888 http://www.openstreetmap.org/browse/changeset/4354864 http://www.openstreetmap.org/browse/changeset/4354839 http://www.openstreetmap.org/browse/changeset/4354783 http://www.openstreetmap.org/browse/changeset/4354745 http://www.openstreetmap.org/browse/changeset/4354677 bashiboy2: http://www.openstreetmap.org/browse/changeset/4354863 http://www.openstreetmap.org/browse/changeset/4354856 http://www.openstreetmap.org/browse/changeset/4354818 http://www.openstreetmap.org/browse/changeset/4354793 ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb -- Gregory o...@livingwithdragons.com http://www.livingwithdragons.com ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] OS StreetView accuracy: caution!
Tim François wrote: I think OS *is* more accurate on the whole, I think you're probably correct, but the problem arises when we *assume* that it's more accurate in areas where we're not knowledgeable of what's on the ground. That's not to say we shouldn't map, but I think we should, as we've been doing before, tag in caveats using the fixme or notes tag to say we're uncertain of certain areas. Cheers Dave F. ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
Re: [Talk-GB] VectorMap District: Completely crazy idea, maybe, but...
Mike Harris wrote: The lack of public right of way information is disappointing - but it is within OSM's capabilities to walk and map it. However, the lack of field boundary information is a serious deficiency as these are invaluable in practice to walkers attempting to plan, navigate, record and publish walks - especially in the more lowland and more farmed areas. Without the OS's right to enter onto private land without any advance permission, OSM mappers will remain seriously hampered in any attempt to map field boundaries. Hedges may be visible in good quality satellite or aerial photography but fences (and especially electric fences) will be very difficult. I agree field boundaries are valuable for walkers, but only those abutting or near PROWS are relevant these are obviously obtainable by walking there. Spring is in the air, put your boots on a go walking! Cheers Dave F. ___ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
