Re: [Talk-us] Virtual Mappy Hours reboot

[Martijn van Exel]

Hi folks!
This is a reminder that we will have our first osm fireside chat / mappy hour 
tomorrow! I will be looking forward to see you then.
Martijn

> On Sep 18, 2017, at 11:46 AM, Martijn van Exel  
> wrote:
> 
> Hey all, 
> 
> I decided to give the Virtual Mappy Hours another go. The first one will be 
> next Wednesday at 5:30 pacific. We’ll talk about State of the Map US. I hope 
> you can join! Details are in this diary entry: 
> https://www.openstreetmap.org/user/mvexel/diary/42318 
> 
> 
> Martijn

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Re: [Talk-us] Recent Aerial Photo Imagery Changes

[Mark Wagner]

On Tue, 26 Sep 2017 11:07:55 +0300
Rihards  wrote:

> On 2017.09.26. 03:09, David Wisbey wrote:
> > Fellow mappers,
> > 
> > So what's up with the recent changes in our aerial photo imagery?
> > 
> > It used to be so simple and I followed the rule(?) of making sure
> > features line up with Bing imagery.  I'm wondering about that now -
> > big time. I have been mapping in a variety of locations lately and
> > the situation is different in each location.  In Minnesota, for
> > instance, I really don't want to use Bing imagery unless at some
> > zoom level it shows me the most current images (especially in high
> > growth areas like northwest Rochester). And when recently updating
> > an intersection in southwest Minnesota to a new roundabout, I was
> > aghast at what Bing was giving me and so only used it where the
> > quality/resolution "wasn't TOO bad". Sad. Mapbox, ESRI and other
> > imagery were all much better choices, especially between Blomkest
> > and Hutchinson, MN.
> > 
> > So the main question now is: Does the "line up with Bing" rule
> > still stand? In recent work around the city of Virginia, Minnesota
> > (re-routing of US 53) I felt I had to use Mapbox imagery and so
> > lined up what I could with it rather
> > than Bing. In most cases, they matched or were off by only 2 meters
> > or so.  
> 
> there has never been a rule to "line up with Bing", quite the
> opposite - you should not unconditionally line up with any imagery
> layer, unless you know for sure it's extremely precise.
> regarding imagery layers like sat/ortophoto, it has always been
> suggested to check and align them to gps traces from the area (while
> keeping in mind that one or few traces might be all wrong, the centre
> line of many traces being the best).

When possible, I line up imagery to Strava cycle heatmaps -- Strava's
already done the work of averaging dozens/hundreds of traces for you.
When doing this, keep in mind that, especially in hilly areas, cyclists
sometimes prefer one direction of travel over another, biasing the peak
to one side or the other.  Alignment to Strava works best when you've
got two distinct peaks from the shoulders of a road, or a single narrow
peak from a dedicated bicycle route.

With the old Bing imagery, I usually didn't bother, since the
disagreement between Bing and Strava was usually less than the
resolution of the imagery.  With the new imagery, I prefer not to use
the imagery unless I can align a nearby feature to something I know is
reasonably accurate (and when mapping locally, I don't use Bing at all
-- ESRI is newer, better-aligned, and has resolution that would let
me map the shingles on a roof.)

-- 
Mark

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Re: [Talk-us] Recent Aerial Photo Imagery Changes

[Volker Schmidt]

> ... it has always been
> suggested to check and align them to gps traces from the area (while
> keeping in mind that one or few traces might be all wrong, the centre
> line of many traces being the best).
>

This is certainly the best advice (unless you are in an area with high
buildings or steep mountains, conditions which may produce systematic GPS
errors, in which case there is no recipe)
Apart from simple shift problems, satellite/areal photos may suffer, even
considerably, from vertical parallax problems. In my area (Northern Italy)
Bing maps have consistently suffered from Lat-Long shift in the order of
even 5 meters plus a superimposed parallax error that deforms road shapes
further, typically in the mountains. The parallax error becomes worse the
steeper the hills/mountains are.
To illustrate the parallax problem, have a look at this example in
California:
https://www.openstreetmap.org/edit?editor=id#map=18/35.99284/-121.48429
Compare the Bing map layer with the Mapbox map layer and also with the GPX
tracks.
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Re: [Talk-us] Recent Aerial Photo Imagery Changes

[Rihards]

On 2017.09.26. 03:09, David Wisbey wrote:
> Fellow mappers,
> 
> So what's up with the recent changes in our aerial photo imagery?
> 
> It used to be so simple and I followed the rule(?) of making sure features
> line up with Bing imagery.  I'm wondering about that now - big time.
> I have been mapping in a variety of locations lately and the situation is
> different in each location.  In Minnesota, for instance, I really don't want
> to use Bing imagery unless at some zoom level it shows me the most
> current images (especially in high growth areas like northwest Rochester).
> And when recently updating an intersection in southwest Minnesota to a
> new roundabout, I was aghast at what Bing was giving me and so only used
> it where the quality/resolution "wasn't TOO bad". Sad. Mapbox, ESRI and
> other imagery were all much better choices, especially between Blomkest
> and Hutchinson, MN.
> 
> So the main question now is: Does the "line up with Bing" rule still stand?
> In recent work around the city of Virginia, Minnesota (re-routing of US 53)
> I felt I had to use Mapbox imagery and so lined up what I could with it
> rather
> than Bing. In most cases, they matched or were off by only 2 meters or so.

there has never been a rule to "line up with Bing", quite the opposite -
you should not unconditionally line up with any imagery layer, unless
you know for sure it's extremely precise.
regarding imagery layers like sat/ortophoto, it has always been
suggested to check and align them to gps traces from the area (while
keeping in mind that one or few traces might be all wrong, the centre
line of many traces being the best).

> I would provide a link to show you the worst area I found (along MN 7
> several
> miles east of Blomkest) but Openstreetmap.org seems to be down right now.
> 
> David
> Your Village Maps
> 
> 
> 
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> 


-- 
 Rihards

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