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

Volker Schmidt voschix at gmail.com
Sat Jan 12 20:57:47 UTC 2019

Let me just inject that the wavy-roads problem is also present at Big G.
Go have a look at

Back to the argument of the thread: Generally speaking, of the maps we have
available for OSM in Italy, the best ones are the oldest ones: PCN2006,
poor resolution but near-perfect position (based on many GPX tracks) and
good parallax correction. The worst are normally Bing. They have not only a
position shift of many meters (that varies with the location), but also
considerable problems with parallax correction, up to tens of meters (very
poor parallax correction on hilly terrain). The others DigitalGlobe, Esri,
Mapbox are in-between, but are have only shifted positions, but not the
parallax problems of Bing.
Obviously I have no idea if Bing in Italy is technically the same as in

On Sat, 12 Jan 2019 at 18:41, André Pirard <a.pirard.papou at gmail.com> wrote:

> On 2019-01-12 06:33, Eugene Alvin Villar wrote:
> 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.
> Bing is sometimes (often? I almost never use it) inconsistent (offset)
> with itself at different zoom levels.
> 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 think that orthorectification uses elevation maps as correction.
> Rather, they combine shots from different angles to compute the position of
> objects and that computes their elevation. A nadir photograph of a building
> is uninteresting because it only shows the roof. Side shots show the walls
> and allow computation of their height and ground location.  Aerial imagery
> shows only one of the many shots they have.
> 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
> good.
> The orthorectification we can use in Wallonia (PICC) is really perfect. Of
> the lines I see it computes in places I know, almost only the center of the
> road can be not wrong but debatable. Sometimes lanes that have been changed
> to parking or things like that are not up to date, but that's manual
> fixing, not orthorectification.
> All the best,
> André.
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