[OSM-talk] What do you wish you'd known?

[Teemu Koskinen]

On Sat, 20 Mar 2010 11:50:13 +0200, John Smith <deltafoxtrot256 at gmail.com>  
wrote:

> On 20 March 2010 19:42, Teemu Koskinen <teemu.koskinen at mbnet.fi> wrote:
>> I wish I had known that the Yahoo aerial images are not rectified, as I
>> blindly went and "corrected" all the roads in my neighborhood by moving
>> them to coincide with the aerial images. In reality they already were in
>> the correct position as they were drawn from more accurate gps-traces.
>
> Someone mentioned this a while back, in terms of editors storing
> corrected image positions centrally.
>

That only helps if the images are just offset by some amount, it doesn't  
help at all if they are warped, rotated etc.
See eg. the centre of Helsinki: http://elanor.mine.nu/daeron/wavy.jpg
All the red lines are completely straight in reality. The whole Helsinki  
area is full of similar errors in the Yahoo aerial images.

Teemu Koskinen