[HOT] Bing imagery offset

Severin Menard severin.menard at gmail.com
Tue Nov 18 18:52:37 UTC 2014


I just updated the job <http://tasks.hotosm.org/project/591> instructions
as proposed below. SUmmary: first Bing 2013, then WV2 to complete.



On Tue, Nov 11, 2014 at 3:48 PM, Severin Menard <severin.menard at gmail.com>

> Hi,
> Yes the adjustments for the latest WV2 imagery, put in the offset db, were
> based on the Bing imagery, supposedly (almost no GPS traces over Juba,
> unfortunately). BUT Bing updated its imagery over Juba; it is now dated
> June 23, 2013 and the georeferencing is slightly different, making the
> previous offset_db points obsolete. Tried to deprecate or delete them, did
> not get it, if someone knows the tip, I would be interested.
> Considering the two imagery are now quite close, I would suggest to:
> - draw first on Bing and consider its georeferecing is good
> - then display the WV2 imagery, correcting the offset manually (was more
> complicated with the previous Bing imagery that was quite dark and quite
> old, what made the offset correction not easy considering the city is
> growing/evolving fast), and add the missing parts (from the test I made,
> new buildings here and there and more new buildings in the city limits, as
> expected).
> It this makes sense for everyone, I edit the job's instructions
> accordingly.
> Sincerely,
> Severin
> On Thu, Nov 6, 2014 at 9:51 AM, Sander Deryckere <sanderd17 at gmail.com>
> wrote:
>> The reason for this is because relative offsets are much harder to deal
>> with than absolute offsets. When the relative positions are correct, you
>> can still calculate how far things are from each other, how big they are,
>> ... You don't need the absolute position for it. Even on the field, when
>> using a GPS, the quality of the GPS position is often so low that you won't
>> notice an absolute offset.
>> To minimise the number of relative differences, it's advised to base your
>> data on a source that's more or less good in quality, and has a big
>> coverage. As such, the Bing imagery was chosen as a base (without an offset
>> applied, as any new mapper would get it in his freshly opened editor).
>> When there are better sources available in the future (f.e. interpolated,
>> high-precision positions), then everything in that region can be shifted by
>> the then-known Bing offset.
>> Regards,
>> Sander
>> 2014-11-06 11:55 GMT+01:00 althio forum <althio.forum at gmail.com>:
>>> Hi HOT
>>> I am on task #591 - South Sudan Crisis, Cholera outbreak in Juba,
>>> mapping with WorldView-2 imagery.
>>> Instructions includes:
>>> Check in the vector data is correctly aligned on Bing imagery. Bing
>>> imagery is the reference for the georeferencing.
>>> My question is about the first step i.e. What is the recommended offset
>>> for Bing imagery:
>>>  (a) get from database
>>>  (b) set to offset: 0.00; 0.00
>>>  (c) other
>>> Cheers,
>>> althio
>>> _______________________________________________
>>> HOT mailing list
>>> HOT at openstreetmap.org
>>> https://lists.openstreetmap.org/listinfo/hot
>> _______________________________________________
>> HOT mailing list
>> HOT at openstreetmap.org
>> https://lists.openstreetmap.org/listinfo/hot
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/hot/attachments/20141118/f6cd29f1/attachment.html>

More information about the HOT mailing list