Hi, I am making some code to view offline tile folders, and need to find the correct folder and file using the GPS coordinates. I "reverse engineered" an offline tile format, and noticed that the folders are determined by longitude and the files in each folder are determined by latitude. I came up with this formula for longitude to find which folder to access given a longitude from GPS:
correctLongitudeFolderToUse = (inputLongitude+180)*((2^currentScale)/360) so if the input longitude is say -120 degrees (west coast) then at a scale of 16 the formula works out to: correctLongitudeFolderToUse =(-120+180)*((2^16)/360) correctLongitudeFolderToUse = 10922.66 This works properly, if I go to the folder with name 10922 the longitude is correct. I have an error for finding which file to access for latitude though. I use this formula for latitude: correctLatitudeFileToUse = (-inputLatitude+90)*((2^currentScale)/180) so if the input latitude is 40 and the scale is again 16 this is the result: correctLatitudeFileToUse = (-40+90)*((65536)/180) correctLongitudeFolderToUse = 18204.44 so in this case it would say the file name should be 18204.jpg in the folder 10922, however the latitude is incorrect. I think it is a scaling error since for the two poles and equator the formula works correctly, and also for 30degrees latitude I think it may work correctly. I think I need a sin or cos term in the formula but not sure. Any ideas on how to fix the latitude formula? cheers, Jamie _______________________________________________ dev mailing list [email protected] https://lists.openstreetmap.org/listinfo/dev
