[Talk-us] [OSM-talk] Imagery parallax error in high altitude areas

Nathan Edgars II neroute2 at gmail.com
Tue Apr 10 04:28:24 BST 2012


On 4/9/2012 11:01 PM, Russ Nelson wrote:
> Nathan Edgars II writes:
>   >  It's not as bad as it seems. Imagery is adjusted using an elevation
>   >  dataset. Since this data doesn't (and shouldn't) include buildings and
>   >  bridges, these appear distorted. You'll also see problems where recent
>   >  heavy construction has caused changes in topography.
>
> Or where the elevation dataset doesn't include a deep canyon, which
> causes a straight bridge to appear curved. If it's a railroad, you can
> be pretty sure it isn't. If it's a road bridge, you have to rely on
> what you saw when you were there.
>
I think this is because the elevation data *does* include the canyon. 
Since the image was taken at an angle, the bridge appears at a different 
place in the canyon, and must curve to reach the correct location at the 
top.

Here, for example: http://mapper.acme.com/?ll=38.06661,-81.08022&z=16&t=O
The camera was to the northwest, so the bridge was on a line with the 
canyon southeast of its actual location. The bridge down in the bottom 
of the canyon is also curved, but much less so because it's smaller. 
It's also in essentially the correct place (as seen by comparing to 
Google's photos and USGS topos).

(crossposted to talk-us because who knows when the talk@ mods will let 
this through)



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