> From: andrzej zaborowski [mailto:balr...@gmail.com] > Subject: Re: [OSM-talk] OT - Unusual Bing imagery > > On 24 July 2012 03:48, Alan Mintz <alan_mintz+...@earthlink.net> wrote: > > At 2012-07-23 16:02, andrzej zaborowski wrote: > >> The area in the screenshot seems to have a higher resolution than > >> satellites can achieve. > > > > > > Is this documented somewhere? Assuming from the look and ratio of > > measurements of the jet that it is a B737, the pic is at z20 > > (~12cm/pel @ middle lats). I was under the impression that all of the > > Bing/Yahoo/Google imagery was still satellite-based, down to z21 > > (6cm/pel). I know Google has spots of "UHR" imagery at z22, but it > > seems they were still referred to as satellite. I've seen individual > > county websites with very nice imagery described as "flyover", as > > though coming from airplane/helicopter, apparently on a contract > basis. > > I've assumed 0.5m/px is the technical limit for satellite imaging, > Wikipedia seems to confirm this more or less: > "The latest commercial satellite (GeoEye 1) has a GSD of 0.41 m > (effectively 0.5 m due to United States Government restrictions on > civilian imaging)."[1] I guess military satellites might have better > parameters, but anything you're likely to see on the web with a higher > resolution will be taken from within the troposphere. > > I've been told once that 0.5m is the usual limit around the world except > Israel of which you're unlikely to see imagery better than 2m due to the > government's threats.
This matches up with what I've heard in discussions with one of the cities about their imagery. Another factor is not the resolution but the image quality. Satellite photos have to go through more air which can cause the loss of some information and lower-contrast imagery. On the other hand, a lot of aerial imagery out there is film-based which does not generally have colour and contrast as good as digital aerial imagery. _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
