On 1 June 2010 15:43, TimSC <mapp...@sheerman-chase.org.uk> wrote: > Is there an easy way to find the tile reference for a given area. I > have found what I need so far by trial and error, but with 400 tiles > it can be a bit of a pain. > > -- > Philip Stubbs > > > Philip, > > A quick sketch on the method to go from tile filename to coordinates. Say we > use the filename su85se.tiff. The "su" part, the "85" part and the "se" part > each give a different northing and easting offset. The must be summed to get > the final bottom left corner position. > > The first offset is basically coarse grid letter offset and is found in a > look up table. The codes are arranged like this: > http://en.wikipedia.org/wiki/File:National_Grid_for_Great_Britain_with_central_meridian.gif > > The "85" is an intermediate offset, I think it is 8x10000 metres east and > 5x10000 metres north. > > The final code can be se, sw, ne, nw for a fine tile offset. The "n" sheets > are offset north by 5000m. The "e" sheets are offset east by 5000m. > > Each tile is 5000m by 5000m, as far as I remember so you can get the > coordinates of the other corners. > > Re-reading your question, I guess you really want the inverse of what I just > described? I hope that helps a little anyway. > > TimSC
Thanks Tim. I had worked out that there was some logic to the tile numbers. Having downloaded the tiles for SU, I wanted to find the tile that contained Warsash. Each tile only covers a small area, so I opened tiles until I recognised an area. Then I tried others near that one to see which way they went. Now I have found Warsash, I can work my may through that tile and the ones beside it with ease. I really asked the question for when or if others start to use the tiles also. Regards, -- Philip Stubbs _______________________________________________ Talk-GB mailing list Talk-GB@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-gb
