Hi, There have been as far as I see two different ideas for storing the imagery calibration data (offsets / control points) in a global database instead of local bookmarks. One was Dermot McNally's proposal to store the outlines of areas with constant offset in the osm database, which hasn't yet been implemented but Dermot says he's on it now. The second, which I just learnt about is Komяpa's offsets server. The latter stores offsets at discrete points, which is the approach I was going to take myself. I've set up a simple server [1] which accepts "create", "modify", "delete" calls for control points, and a "get control points affecting a bbox" call, which would be used by editors to warp the imagery as it's being displayed. I now see that the offset server works similarly and the main thing it lacks is a good user interface to interact with the servers in the editors (I'm sending this to josm-dev but Potlatch authors are also on this list too)
Next thing I was going to do was to try to make josm use the server and then propose a patch, but I found the offset server support already implemented so I decided to ask what everyone thinks about this approach. Specifically the UI may be tricky to get right but it would be useful to come up with one that's good enough to be enabled by default -- last week an osm newbie told me the map data in his area was "completely wrong" which he judged from seeing the data against the Bing imagery, which was about 100m out. To keep the UI simple my idea was that the imagery would be warped in the editor using control points loaded from an external DB. Each point of an image would be moved using the offset values from the three or four nearest control points, where available. There would be a set maximum radius a CP can affect, which could be, say, 6km. If there's only a single control point in some place the pixels at that place would be offset by the amount stored for that CP and linearly less with growing distance from the CP, down to zero offset at 6km. When you add an imagery layer in JOSM, a request is made to the offset server for all control points in the visible bbox + a 20km buffer (for example) for all zoom levels, unless that option was diabled in the preferences. In the mean time imagery is loaded with no offset. If the server returns any control points, the view of the imagery is adjusted using those points. If the user later adjusts the imagery using the "Drag to move the picture" action, a new control point is added locally. To upload local control points to the server, user clicks the imagery layer in the "Layers" panel with right mouse button and selects "Upload <N> control points to offset server" from local menu. The option is only available if the offset server was not disabled in the preferences. Since control points have a min and max zoom level, the editor or the server need to decide betweem them which zoom levels a GCP applies to. Current idea is: * for the "Bing" layer, when a new CP is created in the editor, it applies to the all zoom levels that are covered by the same imagery source. The imagery sources are already available from the Bing API because it is queried for the attribution labels. * for "Yahoo" layers, CPs apply to all zoom levels. * for any other layers, a new CP applies only to the current zoom level. On IRC it was also noted that it would be easy for the offset server to download the tiles for a TMS layer at successive zoom levels and compare the tile contents to see how far they correlate. I'm not going to implement that at this point ;) All of the control points would be visible and further editable through a website to avoid complicating the josm UI. What are other people's ideas? Cheers 1. The control points server works at http://openstreetmap.pl/alignator and the supported requests are the following, reponses are JSON. * /create/<layer-name>/<layer-lat>,<layer-lon>/<min_zoom>/<max_zoom>/<true-lat>,<true-lon>/<osm-username> * /modify/<layer-name>/<layer-lat>,<layer-lon>/<new-layer-lat>,<new-layer-lon>/<version>/<min_zoom>/<max_zoom>/<true-lat>,<true-lon>/<osm-username> * /delete/<layer-name>/<layer-lat>,<layer-lon>/<version>/<osm-username> * /get/<layer-name>/<SW-lat>,<SW-lon>/<NE-lat>,<NE-lon>/<current-zoom> _______________________________________________ josm-dev mailing list josm-dev@openstreetmap.org http://lists.openstreetmap.org/listinfo/josm-dev
