Re: [Talk-GB] bing image alignment

[ael]

On Sat, Sep 14, 2013 at 02:24:31PM +0100, OpenStreetmap HADW wrote:
> On 13 September 2013 19:59, ael  wrote:
> 
> > No one has mentioned the OS gps (passive) stations: for example
> > http://www.openstreetmap.org/browse/node/472420260
> > http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/surveying.html

> Depending on exactly which ground feature represents the station, BIng

Photographs of the Buckland station are here:
http://homepage.ntlworld.com/lawrence_a_e/osm/

You can see part of the "metal fence" = railings in the 2nd picture.
It seems to be a granite block or something similar, rather than
concrete.

I don't seem to have taken a wider view, so I am not absolutely sure
that this is directly behind the crash barrier in the Bing image, but I
think it is.

ael


___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 15 September 2013 11:27, ael  wrote:

>
> It is a few years since I looked at any of this, but it had not occurred
> to me that any copyright issue could arise. They are essentially modern
> trig points. There is a mark on the ground, and their website publishes
> the coordinates. Using these coordinates to position a node on osm
> would constitute republishing? I thought very small extracts of
> copyrighted material were permitted in any case.

It is the standard copyright issue for maps.  There is a relatively
new sort of copyright
called database rights.  Normally for copyright you need to have some
creative input.
Things like addresses and telephone numbers do not have any creative
input.  However
database copyrights mean that the PAF (postcode address file) is
copyright, as is your
 local telephone directory.

With a map, the printed form may be covered by a copyright on the typographical
arrangement, but the individual coordinates of the corners of a
building are matters of fact
and can't, individually be copyrighted.  Nonetheless, once you start
plotting many buildings,
the work involved in compiling the information is recognized by a
database copyright.
 Without database copyrights, there would be on copyright blocks on
converting printed
format maps to vector format.

If you extract a single address from the PAF, to send letter, or a
single number, from the
phone book, to make a call, you are extracting the fact.  If you
create a directory, you
are copying the database.  The former is unrestricted (except by any
contract for confidentiality).
The latter is a copyright infringement.

The OS owns the database copyright on its list of passive stations.
Using the location of one
of them for an isolated survey is just using a fact.  Adding large
numbers of them to OSM is
a copyright infringement unless there is a licence that permits it.
Doing so piecemeal still
creates an infringement (if that were not the case, almost all use of
commercial maps would
be fair game, for a crowd sourced map).

There are hints that the intent was an intent to licence with at most
the equivalent of CC BY,
but I've not seen anything that makes that explicit.

On the other hand some of the references to OSTN02, which is actually
a larger database,
explicitly assert the database copyright, but also seem to release
under a BSD licence, which,
 at most, would require some slight tweaking of copyright
attributions. Please do not do
 anything based on this interpretation without verifying it yourself.

(The copyright on OSM itself is essentially a database copyright.)

>
>> Depending on exactly which ground feature represents the station,
>
> That one is a small stud at ground level on a small concrete block
> all surrounded by a rectangular metal fence maybe 30cm high, roughly 1m by
> 1/2m. I must dig out a photograph.

Having seen OS' photograph, I'm fairly sure this is the feature at
5.2m from the GPS
plot, when viewed on the local Bing datum.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[ael]

On Sat, Sep 14, 2013 at 02:24:31PM +0100, OpenStreetmap HADW wrote:
> On 13 September 2013 19:59, ael  wrote:
> 
> > No one has mentioned the OS gps (passive) stations: for example
> > http://www.openstreetmap.org/browse/node/472420260
> > http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/surveying.html
> 
> It's a pity they aren't all clearly visible on the aerial view, my

I have just checked, and I think the one at Buckland may be visible,
but I need to check with the photographs that I took 4 years ago.
in the current Bing images.

I think that you can make out a small rectangular enclosure behind
the crash barrier, and if I am right that is the "metal fence" that 
I mentioned. The stud of radius maybe 1 or 2cm is in the centre of the
enclosure. All this from memory: need to find the photographs.

ael


___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[ael]

On Sat, Sep 14, 2013 at 02:24:31PM +0100, OpenStreetmap HADW wrote:
> On 13 September 2013 19:59, ael  wrote:
> 
> > No one has mentioned the OS gps (passive) stations: for example
> > http://www.openstreetmap.org/browse/node/472420260
> > http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/surveying.html
> >
> > Can we not use them at least for some reference points?
> 
> Interesting.  Unfortunately it looks as though OS Net slipped past
> their commercial people as they use the term "freely available" on
> their web site without giving a precise legal definition of what that
> means.  Given the intended use (all high accuracy surveys in the UK)
> there seems to be an implication that they aren't claiming a database
> copyright, but OSM will probably need a clearer legal statement.
> OSTN02 seems to have the same licensing uncertainty.

It is a few years since I looked at any of this, but it had not occurred
to me that any copyright issue could arise. They are essentially modern
trig points. There is a mark on the ground, and their website publishes
the coordinates. Using these coordinates to position a node on osm
would constitute republishing? I thought very small extracts of
copyrighted material were permitted in any case.

> Depending on exactly which ground feature represents the station, 

That one is a small stud at ground level on a small concrete block 
all surrounded by a rectangular metal fence maybe 30cm high, roughly 1m by
1/2m. I must dig out a photograph.

> Are the ETRS89 coordinates given on the monument itself, as they would

As far as I recall, there was no indication whatsoever of what it was
nor any text at all.

> It's a pity they aren't all clearly visible on the aerial view, my
> local one, which appears to be within centimetres of Bing, is only

I would be very surprised if the one at Buckland could be seen in aerial
images. I must check. It is quite easy to miss it on the ground 
unless you know what you are looking for and where to look. The tall
grass was enough to hide it.

The biggest problem seems to be that there are only a few on public
land and widely scattered, so of limited use.

ael


___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[ael]

On Fri, Sep 13, 2013 at 08:09:49PM +0100, Andy Mabbett wrote:
> On 13 September 2013 19:59, ael  wrote:
> > No one has mentioned the OS gps (passive) stations: for example
> > http://www.openstreetmap.org/browse/node/472420260
> 
> It's rather ironic that that node carries the note:
> 
>"Position from gps waypoint. Not from OS data which is more accurate."

That was me being lazy :-)

ael


___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 19:59, ael  wrote:

> No one has mentioned the OS gps (passive) stations: for example
> http://www.openstreetmap.org/browse/node/472420260
> http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/surveying.html
>
> Can we not use them at least for some reference points?
>

Interesting.  Unfortunately it looks as though OS Net slipped past
their commercial people as they use the term "freely available" on
their web site without giving a precise legal definition of what that
means.  Given the intended use (all high accuracy surveys in the UK)
there seems to be an implication that they aren't claiming a database
copyright, but OSM will probably need a clearer legal statement.
OSTN02 seems to have the same licensing uncertainty.

I would note that even if a relatively restrictive licence were to
apply, OS allow checking of accuracy, as long as you don't use the
measured error to correct the inaccurate data.

Depending on exactly which ground feature represents the station, BIng
datum), Bing and the consumer grade GPS survey differ by between 5.2
and 6.2m.   Bing and StreetView agree quite well at that point, but
diverge towards the West.  The BIng error in the typical range, at
this point.

Are the ETRS89 coordinates given on the monument itself, as they would
be individual statements of fact, much like an individual address with
postcode?  (OS Net allows for movement, so the highest accuracy values
will not be fixed.)

Without survey quality GNSS receivers, these points are probably
mainly of use for calibrating imagery.

It's a pity they aren't all clearly visible on the aerial view, my
local one, which appears to be within centimetres of Bing, is only
identifiable because OS have measured the distance from the local
trees.  When the rain stops, I'll have a look at what is on the
ground, and try for a long average GPS reading.  I'll also try and get
on the ground measurements from the trees in case the station
coordinates are considered fair game, but the sketch map details
aren't  (looks like a surveyor's tape is on the shopping list - I
guess class III, at about 0.05% is good enough, compared with GPS).

I note that a lot of them are on private land and require permission
from the landowner to gain physical access.

PS.  The OSTN02 conversion tool, which presumably contains the table,
has a BSD Licence, according to
.
 If that is correct, I can see no reason why the os.openstreetmap
tiles should not be rectified based on OSTN02.  The data also seems to
be available in lat/long to lat/long forrmat, also with a BSD licence.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[ael]

On Fri, Sep 13, 2013 at 05:41:04PM +0100, OpenStreetmap HADW wrote:
> My feeling is, that, until we can get our own grid of accurately
> surveyed reference points, we ought choose one source that is better
> than GPS.


No one has mentioned the OS gps (passive) stations: for example
http://www.openstreetmap.org/browse/node/472420260
http://www.ordnancesurvey.co.uk/business-and-government/help-and-support/navigation-technology/os-net/surveying.html

Can we not use them at least for some reference points? 

That said the one above is in a lethal position on the verge of a very
dangerous road: you take your life in your hands getting to it, and then
have to fight the stinging nettles...

ael


___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 14:58, SK53  wrote:

Whilst most of the error terms may well, unfortunately, be true...
>
> OSSV scale is 1 pixel / metre, so accuracy is less than that.

That's a common misunderstanding about spatially, or time quantised
data.  If it were really true, the 300m chip length in GPS would limit
GPS accuracy to much worse than 5m.  This is not just true of
photographic imagery.  It is also true of anti-aliased line art, like
StreetView, or even non-anti-aliased material, as long as lines are
not parallel to the primary axes.  Providing you know what has been
reduced to 1m pixels, and it has sufficient high spatial frequency
component, e.g. footpath edges in aerial imagery and the underlying
vector lines in the maps, one can interpolate to rather better than
1m.
>
> So sources of error are:
>
> Feature generalisation in OSSV, noticeable on buildings & roads

These tend to be local distortions.  By choosing features carefully, I
think you can avoid them when aligning aerial imagery with StreetView.

> Re-projection of OSSV tiles using proj4 using OSGB36, errors of +/- 5m

Errors in the OS survey.

> Given an average road is about 7-8 metres across we are less likely to
> notice this with roads anyway.

Which is why the problem only really starts to show now that there is
extensive, armchair, mapping of individual buildings.


> If one looks at GPS traces for the same footpath walked again and again,
> their spread is quite considerable, perhaps as much as 20 m, although an
> average would probably be close to the actual 2 m path.

Many are mapped on a single pass.

>
> So just like any other survey organisation, ultimately we will need our own
> set of convenient reference points.

Unfortunately, StreetView doesn't seem to have OS' trig points!

My feeling is, that, until we can get our own grid of accurately
surveyed reference points, we ought choose one source that is better
than GPS.  As the US probably uses government maps, for this, now that
they are available to us, they would seem to be the best option.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Richard Fairhurst]

OpenStreetmap HADW wrote:
> Does mapserv use OSTN02?

As Tom has just told you, it uses a GDAL VRT with the source 
projection defined by: 

PROJCS["OSGB 1936 / British National Grid", 
 GEOGCS["OSGB 1936", 
 DATUM["OSGB_1936", 
 SPHEROID["Airy 1830",6377563.396,299.324964644, 
 AUTHORITY["EPSG","7001"]], 
 TOWGS84[375,-111,431,0,0,0,0], 
 AUTHORITY["EPSG","6277"]], 
 PRIMEM["Greenwich",0], 
 UNIT["degree",0.0174532925199433], 
 AUTHORITY["EPSG","4277"]], 
 PROJECTION["Transverse_Mercator"], 
 PARAMETER["latitude_of_origin",49], 
 PARAMETER["central_meridian",-2], 
 PARAMETER["scale_factor",0.9996012717], 
 PARAMETER["false_easting",40], 
 PARAMETER["false_northing",-10], 
 UNIT["metre",1, 
 AUTHORITY["EPSG","9001"]], 
 AUTHORITY["EPSG","27700"]] 

I have looked Really Hard at this and I don't see the entire OSTN02 table in
there. I might be missing something so will continue to stare hard at it.

Frankly all of this is a vast distraction; the tiny amount of alleged
"inaccuracy" resulting from all of this is about one-zillionth of the click
accuracy of your average OSM tracing monkey. If you're really concerned with
improving OSM accuracy then there are lots of roads in rural Wales out by
>50m that could do with realigning.

cheers
Richard

P.S. everyone else on this list is identifiable by their real name. It would
be lovely if you were too, thank you :)




--
View this message in context: 
http://gis.19327.n5.nabble.com/bing-image-alignment-tp5776863p5777498.html
Sent from the Great Britain mailing list archive at Nabble.com.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 14:46, Tom Hughes  wrote:
> On 13/09/13 14:28, OpenStreetmap HADW wrote:
>
>> How does one find that out for the tiles served by
>> os.openstreetmap.org, and if they are not using the high accuracy
>> conversions, why not?  (OS' own online viewer also uses WGS84
>> coordinates to label their tiles - suggesting that they should be
>> using the high quality WGS-84 calibration.)
>
>
> They are produced using mapserv from a gdal vrt with the source projection

Does mapserv use OSTN02?

> defined by:
>
> PROJCS["OSGB 1936 / British National Grid",

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[SK53]

AFAIK all OS StreetView tiles on OSM are projected in Spherical Mercator
and this reprojection will certainly have been done using proj4, i.e, it's
algorithmic not table-driven.

OSSV scale is 1 pixel / metre, so accuracy is less than that.

So sources of error are:

   - Feature generalisation in OSSV, noticeable on buildings & roads
   - Re-projection of OSSV tiles using proj4 using OSGB36, errors of +/- 5m
   - Known GPS signal errors (LDOP)
   - Unknown & systematic GPS errors
   - Fudge factor in aligning these two sources
   - Human factors in interpreting alignments

Taken together this suggests 6-10 metres is entirely in the range that we
might expect & that keeping topological relationships is more important.
Given an average road is about 7-8 metres across we are less likely to
notice this with roads anyway.

Obviously an aerial imagery source introduces a number of other error
sources.

If one looks at GPS traces for the same footpath walked again and again,
their spread is quite considerable, perhaps as much as 20 m, although an
average would probably be close to the actual 2 m path.

So just like any other survey organisation, ultimately we will need our own
set of convenient reference points.

Jerry


On 13 September 2013 14:37, OpenStreetmap HADW  wrote:

> On 13 September 2013 14:22, Colin Smale  wrote:
> > Cm-level GPS accuracy is coming within our grasp... My attention was
> > recently drawn to this:
> >
> > http://www.kickstarter.com/projects/swiftnav/piksi-the-rtk-gps-receiver
> >
>
> You need to operate in differential mode to get the full accuracy,
> which means you still need an accurately surveyed datum.
>
> I don't see that it will help with reflections.
>
> I also wonder if it will prompt the re-introduction of selective
> availability, as it gives some of the advantages of the higher
> chipping rates on the, encrypted, find mode GPS signal, and probably
> doesn't have the velocity and altitude caps normally applied to
> commercial receivers.  I believe the military have the advantage that
> they can use the second frequency to help do large area ionosphere
> corrections.
>
> ___
> Talk-GB mailing list
> Talk-GB@openstreetmap.org
> https://lists.openstreetmap.org/listinfo/talk-gb
>
___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Tom Hughes]

On 13/09/13 14:28, OpenStreetmap HADW wrote:


How does one find that out for the tiles served by
os.openstreetmap.org, and if they are not using the high accuracy
conversions, why not?  (OS' own online viewer also uses WGS84
coordinates to label their tiles - suggesting that they should be
using the high quality WGS-84 calibration.)


They are produced using mapserv from a gdal vrt with the source 
projection defined by:


PROJCS["OSGB 1936 / British National Grid",
GEOGCS["OSGB 1936",
DATUM["OSGB_1936",
SPHEROID["Airy 1830",6377563.396,299.324964644,
AUTHORITY["EPSG","7001"]],
TOWGS84[375,-111,431,0,0,0,0],
AUTHORITY["EPSG","6277"]],
PRIMEM["Greenwich",0],
UNIT["degree",0.0174532925199433],
AUTHORITY["EPSG","4277"]],
PROJECTION["Transverse_Mercator"],
PARAMETER["latitude_of_origin",49],
PARAMETER["central_meridian",-2],
PARAMETER["scale_factor",0.9996012717],
PARAMETER["false_easting",40],
PARAMETER["false_northing",-10],
UNIT["metre",1,
AUTHORITY["EPSG","9001"]],
AUTHORITY["EPSG","27700"]]

Tom

--
Tom Hughes (t...@compton.nu)
http://compton.nu/

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 14:22, Colin Smale  wrote:
> Cm-level GPS accuracy is coming within our grasp... My attention was
> recently drawn to this:
>
> http://www.kickstarter.com/projects/swiftnav/piksi-the-rtk-gps-receiver
>

You need to operate in differential mode to get the full accuracy,
which means you still need an accurately surveyed datum.

I don't see that it will help with reflections.

I also wonder if it will prompt the re-introduction of selective
availability, as it gives some of the advantages of the higher
chipping rates on the, encrypted, find mode GPS signal, and probably
doesn't have the velocity and altitude caps normally applied to
commercial receivers.  I believe the military have the advantage that
they can use the second frequency to help do large area ionosphere
corrections.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 13:38, Phil Endecott  wrote:
> OpenStreetmap HADW wrote:

> When using any OS data it's important to be certain of the method used
> for the datum conversion.  If it's not using the OSTN02 table-driven


How does one find that out for the tiles served by
os.openstreetmap.org, and if they are not using the high accuracy
conversions, why not?  (OS' own online viewer also uses WGS84
coordinates to label their tiles - suggesting that they should be
using the high quality WGS-84 calibration.)

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Colin Smale]

Cm-level GPS accuracy is coming within our grasp... My attention was
recently drawn to this: 

http://www.kickstarter.com/projects/swiftnav/piksi-the-rtk-gps-receiver
[2] 

On 2013-09-13 15:06, OpenStreetmap HADW wrote: 

> I don't think I would trust commercial GPS much below 5m unless it was
> 
> averaged over at least an hour, with a clear view of the sky
> (reflections off builidngs could systematically distort the position
> solution - see http://wiki.openstreetmap.org/wiki/Accuracy#Systematic_errors 
> [1]).
> Where I've looked into calibrating against GPS I've tended to find
> that there are good places that are accurately locatable on Bing where
> you can sit with GPS for a long time without looking suspicious, and
> which are near to points of interest and have a clear view of the
> sky.



Links:
--
[1] http://wiki.openstreetmap.org/wiki/Accuracy#Systematic_errors
[2]
http://www.kickstarter.com/projects/swiftnav/piksi-the-rtk-gps-receiver
___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 12:55, Chris Hill  wrote:
> Why do you suppose OS Streetview is correct? I find that compared to multiple 
> GPS tracks it is not always well aligned and more recent Bing imagery is 
> often better.

I did consider that possibility, but I did a search for that  and it
came up suggesting StreetView was mostly good to about 1m (although I
can't re-find that reference).  On the other hand, that is a reason
for requiring more evidence before correcting things which assume zero
offset for Bing.

As noted elsewhere on this thread, Bing clearly shows parallax errors,
and it looks like it hasn't been corrected for height variations, at
least not on a local scale.

I don't think I would trust commercial GPS much below 5m unless it was
averaged over at least an hour, with a clear  view of the sky
(reflections off builidngs could systematically distort the position
solution - see http://wiki.openstreetmap.org/wiki/Accuracy#Systematic_errors).
 Where I've looked into calibrating against GPS I've tended to find
that there are good places that are accurately locatable on Bing where
you can sit with GPS for a long time without looking suspicious, and
which are near to  points of interest and have a clear view of the
sky.

On the other hand, pre-OpenData specifications for StreetView suggest
worst case errors of 4.1m
, so, maybe
 I'm still going to have to do long averaged GPS calibrations.

That still doesn't mean that unsourced BIng tracings, with zero
offsets are good things.

Fortunately, OSM hasn't been around enough for continental drift to
become a severe problem.  Even the error since 1984 should be less
than about one foot.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Phil Endecott]

OpenStreetmap HADW wrote:

A couple of days ago, I walked a footpath, which turned out, along
with the preceding private road, to be a PROW on foot.  As I wanted to
detail map it to show steps, I first calibrated Bing against OS
StreetView


When using any OS data it's important to be certain of the method used
for the datum conversion.  If it's not using the OSTN02 table-driven
conversion you should expect to see offsets.  The OS documentation says
that the less-accurate method is OK for up to +/- 5m, but my experience
is that the offset can be greater than that, e.g. up to about 20m.
If you ever see offsets of this magnitude in anything that has touched
OS grid references or OSGB36 datum, be suspicious!

(As an example, http://hills-database.co.uk/ *deliberately* uses the
less-accurate conversion because they claim that GPS devices will
typically use the less-accurate conversion back to WGS84 when you
enter a grid reference.  As a consequence, if you display their
summit positions on a not-reprojected OS map, they will be in the
wrong places.)


Cheers,  Phil.





___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 13 September 2013 12:31, Colin Smale  wrote:
> Which is the higher priority, consistency or accuracy? Is it better to have
> an internally consistent map, where everything is topologically correct but
> possibly a little displaced by a uniform vector, or is it better to have
> some of the objects positioned with high accuracy, despite the apparent
> conflicts with the rest?

The case in question is not internally consistent!  The main roads are
more correctly placed than the buildings.  This doesn't stand out like
a sore thumb because the roads and pavements are wide enough to take
up the slack.  However, a 1m wide footpath, sandwiched between two
buildings, and displaced by about 6m does stand out.

The other risk is of a gradual, but not as gradual as continental
drift, creep as features get added relative to misplaced features
placed relative to misplaced features.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Chris Hill]

Why do you suppose OS Streetview is correct? I find that compared to multiple 
GPS tracks it is not always well aligned and more recent Bing imagery is often 
better. 

OpenStreetmap HADW  wrote:
>On 10 September 2013 10:09,   wrote:
>
>> This has been discussed on the list before. Bing image alignment can
>be
>> quite poor
>
>One unfortunate consequence of this is that there are areas of the map
>where the majority of features are out of position by 15 or more feet,
>because people have added large numbers of buildings, from Bing,
>whilst treating the Bing locations as gospel.
>
>A couple of days ago, I walked a footpath, which turned out, along
>with the preceding private road, to be a PROW on foot.  As I wanted to
>detail map it to show steps, I first calibrated Bing against OS
>StreetView, and moved both the road and path accordingly.  The result
>is that it now goes right though the last building to actually be
>mapped on the road where the path ends.  Looking at all the,
>un-sourced, (another gripe is the amount of material going in with no
>source and often no comment, but often quite extensive) buildings in
>the area, they seem to align perfectly with uncorrected Bing images.
>
---
cheers, Chris
osm user, chillly

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Colin Smale]

Which is the higher priority, consistency or accuracy? Is it better to
have an internally consistent map, where everything is topologically
correct but possibly a little displaced by a uniform vector, or is it
better to have some of the objects positioned with high accuracy,
despite the apparent conflicts with the rest? If we are going to get
fussy about the accuracy of OSM objects, things aren't going to get
mapped. My vote would go with a consistency based approach; at least all
the objects will be wrong by the same amount, which might even be
machine-correctable. But I will probably get shot down 

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 10 September 2013 10:09,   wrote:

> This has been discussed on the list before. Bing image alignment can be
> quite poor

One unfortunate consequence of this is that there are areas of the map
where the majority of features are out of position by 15 or more feet,
because people have added large numbers of buildings, from Bing,
whilst treating the Bing locations as gospel.

A couple of days ago, I walked a footpath, which turned out, along
with the preceding private road, to be a PROW on foot.  As I wanted to
detail map it to show steps, I first calibrated Bing against OS
StreetView, and moved both the road and path accordingly.  The result
is that it now goes right though the last building to actually be
mapped on the road where the path ends.  Looking at all the,
un-sourced, (another gripe is the amount of material going in with no
source and often no comment, but often quite extensive) buildings in
the area, they seem to align perfectly with uncorrected Bing images.

It is easy to perpetuate such problems by using the existing buildings
to calibrate further additions.

I'm reluctant to correct such bulk errors unless I can find somewhere
to safely sit a GPS for several hours, with a clear view of the sky
and good landmarks on  aerial imagery photographs, to get absolute
proof of the error.  (I don't plan to hire a DGPS receiver!).  Also,
without an explicit source, everything needs carefully checking to
make sure that it is consistent with the same flawed source.

Often the main roads are more accurate in these areas, because they
come from older sources, although I sometimes wonder what those were,
too.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[osm]

On Tue, 10 Sep 2013 09:29:24 +0100, Lester Caine 
wrote:
>> One reason for this is parallax error, because the images aren't
>> taken square on to the ground (that may be because the camera is
>> taking in quite a large area.  You can see this with building, you
>> can end up with a metre or more difference depending on whether you
>> use the top or bottom of the building.  It also presumably means
>> that alignment changes with the height of the land.
>
>Obviously this pass is well over from the last one, which was pretty
>well aligned. There is quite a steep slope on the area I was working
>on last night and I can align things to the bottom or the top of the
>slope ... -1.68; -5.13 at the top
>-6.92; -8.13 down the slop :)
>

This has been discussed on the list before. Bing image alignment can be
quite poor where there are steep elevation changes. I see this a lot
around the Devon coast where a lot of the settlements are on steep
slopes.

Google seem to handle this a lot better. Whether they spend more
capturing the imagery or have some better way of post processing it who
knows?

Kevin

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[Lester Caine]

I started answering this a couple of hours ago, but as I was documenting things 
I was also testing what I'd written. I'm a lot more comfortable with the FACT 
that new new bing imagery around here can't be used without several different 
offsets. Previously there was not much difference between zoom levels and 
'height' above sea level. In-line comments are 'chronological' :)


OpenStreetmap HADW wrote:

On 9 September 2013 20:05, Lester Caine  wrote:

I'm currently playing in an area where the highest resolution imagery is
still an older view, while as I zoom out we step to newer imagery which is
some distance off from the map tracks. I'm fairly happy with the map as I
have had some older gps tracks which it follows, and I'll run over in the
morning and gather a new track as a cross reference, but are people in
general finding that these new images are out of alignment with what is
currently mapped? Can I assume that they need realigning before using them?


I find that current BIng is usually mis-allgned by two or three metres
relative to OS StreetView, which I believe is good to better than 1
metre.


I think I'm seeing considerably more than that this morning. Both z18 and z19 
layers have now updated to new imagery, but z20 is still the older view. Anybody 
know how to get the size of the change from iD's realignment tool? Not that iD 
is usable as the new imagery is so dark you can't distinguish features. I really 
need the potlatch2 'dim' feature to make these images usable!


OK - JOSM is saying 5.5 meters + depending on height ... SSW

AH - So that is how you do it in Potlatch2 ( shift + slide )
I should probably get used to josm's different hotkeys - I've currently got 
three offsets set up in that.



One reason for this is parallax error, because the images aren't taken
square on to the ground (that may be because the camera is taking in
quite a large area.  You can see this with building, you can end up
with a metre or more difference depending on whether you use the top
or bottom of the building.  It also presumably means that alignment
changes with the height of the land.


Obviously this pass is well over from the last one, which was pretty well 
aligned. There is quite a steep slope on the area I was working on last night 
and I can align things to the bottom or the top of the slope ...

-1.68; -5.13 at the top
-6.92; -8.13 down the slop :)


On the the other hand, individual GPS points usually have larger error
than this.  With commercial grade GPS, you probably need several hours
averaging to get down to a metre accuracy.


The S4 GPS is poor on accuracy, unless snap to road is on you end up driving 
through the fields, but I have a new USB module for the tablet which is a lot 
more accurate. Obviously a dedicated receiver has a better aerial and I'll take 
a run up on top when I pop out to the bank later.


Work in progress 

--
Lester Caine - G8HFL
-
Contact - http://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
Model Engineers Digital Workshop - http://medw.co.uk
Rainbow Digital Media - http://rainbowdigitalmedia.co.uk

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
https://lists.openstreetmap.org/listinfo/talk-gb

Re: [Talk-GB] bing image alignment

[OpenStreetmap HADW]

On 9 September 2013 20:05, Lester Caine  wrote:
> I'm currently playing in an area where the highest resolution imagery is
> still an older view, while as I zoom out we step to newer imagery which is
> some distance off from the map tracks. I'm fairly happy with the map as I
> have had some older gps tracks which it follows, and I'll run over in the
> morning and gather a new track as a cross reference, but are people in
> general finding that these new images are out of alignment with what is
> currently mapped? Can I assume that they need realigning before using them?



I find that current BIng is usually mis-allgned by two or three metres
relative to OS StreetView, which I believe is good to better than 1
metre.

One reason for this is parallax error, because the images aren't taken
square on to the ground (that may be because the camera is taking in
quite a large area.  You can see this with building, you can end up
with a metre or more difference depending on whether you use the top
or bottom of the building.  It also presumably means that alignment
changes with the height of the land.

On the the other hand, individual GPS points usually have larger error
than this.  With commercial grade GPS, you probably need several hours
averaging to get down to a metre accuracy.

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-gb

[Talk-GB] bing image alignment

[Lester Caine]

I'm currently playing in an area where the highest resolution imagery is still 
an older view, while as I zoom out we step to newer imagery which is some 
distance off from the map tracks. I'm fairly happy with the map as I have had 
some older gps tracks which it follows, and I'll run over in the morning and 
gather a new track as a cross reference, but are people in general finding that 
these new images are out of alignment with what is currently mapped? Can I 
assume that they need realigning before using them?


--
Lester Caine - G8HFL
-
Contact - http://lsces.co.uk/wiki/?page=contact
L.S.Caine Electronic Services - http://lsces.co.uk
EnquirySolve - http://enquirysolve.com/
Model Engineers Digital Workshop - http://medw.co.uk
Rainbow Digital Media - http://rainbowdigitalmedia.co.uk

___
Talk-GB mailing list
Talk-GB@openstreetmap.org
http://lists.openstreetmap.org/listinfo/talk-gb