[Tagging] Imagery variations/misalignments in iD - which to use?

Eugene Alvin Villar seav80 at gmail.com
Sat Jan 12 05:33:36 UTC 2019

On Sat, Jan 12, 2019 at 8:26 AM John Willis <johnw at mac.com> wrote:

> The issue I am facing is that, even after some adjustment of the angle of
> bing imagery, there seems to be some distortion. things don’t line up well
> between the Bing and ortho maps in some places, and are much closer in
> others.  a *lot* of the mapping aligns with the bing imagery, but there are
> areas of obvious 2-3m distortion in places (the road is wavy), but other
> areas of newer/clearer imagry align with the ortho imagry.

I also encounter this "wavy" roads in imagery. I think they are the result
of improper orthorectification by the imagery provider. Satellite imagery
is often off-nadir (not photographed straight down) so providers correct
for differences in terrain elevation by rectifying them based on available
elevation models. Unfortunately, many elevation models like SRTM cannot
distinguish between buildings and hills and so roads are often distorted
around tall buildings in many parts of the world.

I don't have any good solution for this aside from trying to get access to
better imagery so I just try to map things as best as I can. It may also
help to avoid micromapping unless you are sure that the imagery is really
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