Changes between Version 1 and Version 2 of DevWikiRealParameters
- 09/17/11 13:15:30 (20 months ago)
v1 v2 66 66 * s,,y,,^2^ = a,,21,,^2^ + a,,22,,^2^ 67 67 68 69 68 70 Checking this against the wikipedia page on the [http://en.wikipedia.org/wiki/World_file world file], which lists: 69 71 * "pixel width" = s,,x,, = sqrt(A^2^ + D^2^) = sqrt(a,,11,,^2^ + a,,21,,^2^) … … 72 74 Clearly, this does not match the answer on our page. The three possibilities are: we made a mistake; they made a mistake; or no one made a mistake, but we're using different models... The world file page does not declare it's assumptions about what operations are performed, or which order they are performed in. The world file page, however, also defines it's parameter A (for us: a,,11,,) as "pixel size in x direction". 73 75 74 75 76 '''NOTE: If the order of the model operations changes, in particular if scaling and rotation are swapped, then these pages match wikipedia.''' However, the math on wikipedia is unsourced. Since it has become clear that order is vital, and it is by no means guaranteed that all software performs uses the same model, it is probably vital to go out and determine which software performs the calculations which way before we do anything else.