[Tagging] Off Topic: alignment point help

Martin Koppenhoefer dieterdreist at gmail.com
Thu Jun 11 08:49:04 UTC 2015


2015-06-11 10:14 GMT+02:00 johnw <johnw at mac.com>:

>
> I know the precision isn’t so important, but I want everything to be the
> same relative location. The relative position is very important to me. I
> know distortion can skew that, for hills and the like.
>


yes, I have seen it a lot, Bing has a lot of distortions, you align one
building edge and the neighbour is out of alignment. Initially you don't
know which aerial imagery to trust more, but with the time and adding GPS
traces to the game, I have concluded for my area that Bing is inferior
compared to the official imagery (but has a bit higher resolution).
Sometimes you can even see this within Bing (different zoom levels don't
align).




>
> I was also under the impression there was a plugin for JSOM that offered
> automatic imagery offset correction, something which I don’t have access to
> in iD
>


the offsets are not "automatically" created, it is still mappers who do it,
but they are centrally stored and you can access the offsets other people
have uploaded. More info here:
http://wiki.openstreetmap.org/wiki/Imagery_Offset_Database




> I also deal with places where the tracings/imports are 2-5 years old,
> nowhere near aligned to the imagery, has several 20m shifts every few KM,
> so who knows what is right
>


yes, that's the main problem, decide what is "right" ;-)
Do you have GPS traces in this area? They might help in the decision.



> Mappers using JSOM to come in and start moving all major roads over 1 lane
> width and leave all the residential and alleys alone - effectively ruining
> their relative positions and distorting all the intersections. This
> happened *all the time* until I started requesting an alignment point from
> JSOM users.
>


yes, happens with users of other editors as well (e.g. PL, iD), actually in
my area it happens more often by users of the latter, because these editors
are not capable of displaying the better official imagery (distributed via
WMS) and are "forced" to use Bing.



>
> I sometime micromap very tiny places, which means the space between the
> roads, and when mapping towns/areas I include every single possible road
> (alleyways and residental) - and having someone come through and move only
> the trunk road over 2 meters throughout 20 sq km of residential roads I
> just meticulously aligned is a PITA. It is impossible for me to select and
> shift 100,000 points 2 meters over.
>


yes, that's easier in JOSM to do. Shifting literally 100,000 points will
create you problems in any case (changeset limits), but that would be a
quite big area anyway.



> and now I’m starting to map landuse polygons and buildings (correcting
> horribly sloppy work) - but if I lay down all of these objects, someone
> coming in and shifting the road 2m Southeast makes everything look bad.
>


2m is something you hardly notice, I guess we are talking a bit more
(5-10-20 m)?



> If I have someone using JSOM align a polygon that is easy for me to align
> my map to each time I start iD, it is much less likely to occur.
>


you may find one offset here and 20 meters far from that (that's not more
than a single building) a different offset


Cheers,
Martin
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