Changeset: 56940347
sidewalk, road, and other alignment updates.
Closed by speaketh
Tags
changesets_count | 62 |
---|---|
created_by | iD 2.7.0 |
host | https://www.openstreetmap.org/edit |
imagery_used | Bing aerial imagery |
locale | en-US |
Discussion
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Comment from freebeer
Hallo,
I am afraid that in this changeset, you used bad satellite imagery to move a building 5 metres, when using much better aerial overflight imagery from the ESRI Comminity up to a sharp detailed zoomlevel 21 will also show the road you bent, really does not fallow that shape. -
Comment from speaketh
Hi,
Thanks for the feedback. Can you elaborate on how "good" vs "bad" imagery is determined? What is the reference/standard? -
Comment from freebeer
Sorry for the delay.
There is probably a wiki page in english about aerial imageries.
Me, I go from experience viewing various imageries all over.
I just got through writing a lengthy analysis of the available imageries in New York, where a poor victim used the default which is nearly ten metres off from all the alternatives.
But when I moved into a nearby town in the changeset, the imageries were completely different from how I described, so every area I have to analyse independently.
.
The reference would be surveyor-grade GPS points and seeing how well they line up. As this is not practical, some sources of imageries will list their resolution and typical accuracy.
In general, the more detail, I expect the more care is taken to be correct. When available, the Bing z20 imageries show such distortions of buildings to make it appear they are viewed from above, that I assume their elevation models are pretty good.
More detail does not necessarily mean better, as I've seen places where the Mapbox detailed imagery shows a 3 metre offset of a ground-level sidewalk between different overhead passes, despite most buildings appearing to be filmed from overhead rather than at an angle.
But as a general rule, I've found the USGS low-resolution matches well the archived Bing aerials as ESRI Classic, and Bing z20 where available, and I cycle through all the available imageries to get a feel for relative age and clarity of each as well as obvious offset.
In your area here, ESRI looks to be older than Mapbox, but both are well under a metre of each other at one building top I checked.
However at ground level, where ESRI Classic matches newer ESRI, Mapbox shows about 2m offset yet is close to USGS position in its blurriness.
The Bing and other DigitalGlobe Standard imageries both are satellite and show significant perspective distortion, which means items at different elevations like a straight line over a hill or through a valley will appear curved.
A 46 metre high building (from the data) shows 16m of offset from base to roof...
.
In summary, for mapping Arlington, either ESRI or Mapbox is the best choice, although I would have to check over a larger area than the three city blocks to catch my interest. The metre or two difference is acceptable, and not worth moving anything for.
It appears that what you have not yet adjusted at North wilson and North Edgewood was aligned to ESRI. South of there at Clarendon you can see the difference. 6m here. If anything, since the Mapbox imagery is newer, most things have probably been traced from ESRI, so I would verify that then align Mapbox as background to match just for consistency, until someone can show otherwise or offers still better imagery.
Okay, I've typed far too much. I'm sorry. -
Comment from speaketh
Thanks for the very detailed response. I'll read more on the above topics before continuing my edits / correcting earlier edits.
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