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

[Nathan Edgars II]

On 4/1/2012 10:53 AM, Arun Ganesh wrote:
> It recently struck me while identifying mountain peaks in the himalayas
> that something may not be right. All of us have noticed that the top of
> skyscrapers is off from the base of the building owing to parallax error
> of the satellite capturing the image at an angle. The average seems to
> be around a 0.2m displacement for every 1m increase in height (based on
> calculations made in a couple of cities in India). For an imagery tile
> which has 1000m variation in elevation, various objects could be
> displaced by as much as 200m from its real position.

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.