[OSM-talk] satellite precision
Lars Aronsson
lars at aronsson.se
Fri Jan 26 23:28:53 GMT 2007
Dave wrote:
> I think it more likely they just haven't bothered to sync them up very well,
> or for some reason they can't.
There's a kind of visual error called a parallax, which can happen
if you try to measure a drawing with a ruler that isn't flat on
the paper, http://en.wikipedia.org/wiki/Parallax
I think some of the Google maps error between map and satellite
image can be explained by an error in the altitude estimate:
S
/
/
--------z--Y------- A
/
/
- - - - X - - - - - B
S = satellite; B = real altitude of the ground; X = real object on
the ground; A = ground altitude estimated by the satellite
company; Y = image of object X on the satellite image; z = where
the object should have been instead of Y; distance z--Y = error.
You can see from the satellite imagery that the satellite isn't
straight above the target (in zenith). If it is off to the south,
displaying the southern facade of tall buildings, the parallax
error described above should also be off to the north or south, to
the extent that A>B or A<B.
--
Lars Aronsson (lars at aronsson.se)
Aronsson Datateknik - http://aronsson.se
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