[Tagging] Off Topic: alignment point help

Thu Jun 11 13:27:58 UTC 2015

Sent from my iPhone

> On Jun 11, 2015, at 5:49 PM, Martin Koppenhoefer <dieterdreist at gmail.com> wrote:
> 
> 
> 
> 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).

Yea, there is a lot of distortions in the older imagery. 

Bing recently added a 6x6km chunk of brand new imagery (seemingly a single source picture or mosaic) of the largest town in my area, with much greater resolution (10cm?) - so i mapped every single road in that town - doubled the number or residential roads, added about the same number of alleys. The newest bing imagery is as good as google's

The old bing imagery looks like it was taken by a ballon camera in 1883. 

I know bing is buying imagery, and our different places probably have different sources - maybe its the luck of the draw. 

>  
>> 
>> 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 will read up how to use it. 

>> 
>> 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.

I was stupid and forgot to check the gps layer - usually user mfuji helps me with alignment points - and my iphone gps traces are not nearly accurate enough for my area so i stopped looking for them - but yea - i bet there are a ton of traces near the international airport. 

>> 
>> 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.
> 

What is this "wms" you speak of? I didn't know there was another imagery source JSOM was able to use over iD

>  
>> 
>> 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)?
>  

When I am mapping crosswalks and trees into the pedestrial area around a train station, moving the main intersection's trunk road from the center of the road to the southeast corner of the road (at a large intersection) is rather ugly. - so I do mean 2-4m. 

20m means my align point was really off the mark. 

> 
>> 
>> 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
> 

Thanks for all the thoughtful replies!

Javbw
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tagging/attachments/20150611/40bda165/attachment.html>