On Sun, 6 Nov 2011 19:38:06 +0900 Andrew Errington <a.erring...@lancaster.ac.uk> wrote:
> Hi everyone, > > Forgive me if this has been covered elsewhere, but I am wondering what can be > done about the need for aerial photo offsets. There's very little in the > wiki[1] > > In Korea (as elsewhere, I assume) the aerial photos are not always accurately > aligned with reality. Across the country different offsets are needed > (sometimes no offset). What I do is look for a set of GPS traces from a very > visible landmark and then use them to align the aerials. If there are none I > will often find a visible landmark, such as a park, or a running track in a > stadium, and make several GPS traces of my own on different days, so that I > can use them to line up the aerials. I know that one trace is insufficient. > When I first got my GPS (Garmin GPS 60) I traced the fence lines at home. I found that the accuracy was not very good - between +- 12 to 30 metres so I traced the GPS unit on the top of each post so I could accurately repeat the logging then took readings each day, at different times, and plotted them in a CAD program with a circle centred on the reading with a radius of the error range. At the end of the month almost all the circles were reduced to under 1/2 a metre. I guess everyone knows this trick. mick _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
