On Dec 7, 4:40 pm, kfj <[email protected]> wrote: > It looks like there has been a great effort > done on the data already, with hundreds of thousands of individual > maps already vectorised. Is that so? And how did they do it? This is > the information I'm refering to (sorry, my french is a bit rusty, so > I'm not 100% certain if I interpret this correctly): > > http://wiki.openstreetmap.org/wiki/WikiProject_France/Cadastre
Yes, most of the maps are already vectorized by the cadastre departments, making the job for OSM much easier. The rest is still in raster. Among the raster ones, there is an undefined number of maps (probably <5%) using a so-called "local" coordinate system (vs. France-wide systems like Lambert). This local CS's are a challenge, because even the relevant cadaster departments can't define them (I called them, they are still trying to find out). > The data being from an official source, hey, even the cadastre, I > reckon their scales are correct. Like the images you posted are > 1:2000. The problem is to put this scale in relation with the pixels - I can't. So I have to rely on the control points for the proper scaling. > I would like to give you a good answer about how to convert a > scale into a Z parameter, but the connection is non-obvious. It is > certainly not as straightforward as linear distances along the optical > axis. I'll try and find it out, though. OK, great, thanks ! > Now I'm not sure if I understand where this is going. My understanding > of OSM is that the project's aim is to create a vector map of the > earth. Vectorization is done piecemeal, so I don't see why you need > very large raster maps. Hugin is well capable of dealing with large > images (I'm not sure what the actual limit is, but I suspect it's > beyond anyone's memory), but you wouldn't want to vectorize from a > gigapixel map. Why first create one and then chop it into tiles if you > can create a set of maps each of resonable size (like some 100 MBs) > and use those as backdrop for vectorisation? This is what I want to do, and a reasonable piece is one town. But putting together the 24 submaps with a precision that allows to read the street names brings me to 200Mpix. Even if Hugin can generate this kind of file, importing it in JOSM will be a problem. > Okay, granted. Just keep in mind the error sources. I don't know how > accurately you can georefernce with JOSM, since I'm a QGIS user... Georeferencing in JOSM is pretty bad. I should give QGIS a try soon. But globally, my idea was to stitch the pieces first, because georeferencing a big map is easier and faster than georeferencing 24 submaps (assuming they are precise and consistent) > The data look to me as if they had precise grid references. I'd assume > it doesn't get better than that, please correct me if I'm wrong. If > you know the projection, the grid crossing points that are marked on > the map should be perfect for georeferencing the sheets. Are you sure > you are using the proper projection for the map data? What is the > projection, by the way? Unknown, unfortunately :( Otherwise I would georeference the submaps. -- You received this message because you are subscribed to the Google Groups "Hugin and other free panoramic software" group. A list of frequently asked questions is available at: http://wiki.panotools.org/Hugin_FAQ To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/hugin-ptx
