[Talk-GB] Question regarding OS Opendata

[tony wroblewski]

Thanks for the information.

With regards to buildings, What I mean is that normally I add both an
OpenData transparent layer and the bing layer in JOSM, and can see that
sometimes they align quite nicely, and sometimes there is a noticable
difference. People seem to generally map buildings using the bing layer
without any alignment, or taking parallax into account.

Generally I like to believe that the ordnance survery data is more correct,
but sometimes it contains large errors, such as missing, badly shaped
forests or completely missing buildings. I'm guessing it's quite difficult
to get it really accurate, even when using a GPS, so I guess it's best to
stick to whichever is the most accurate.

Tony



On 27 December 2013 18:09, David Woolley <forums at david-woolley.me.uk> wrote:

> On 27/12/13 15:07, tony wroblewski wrote:
>
>> Hi
>>
>> I have a question regarding the OS Opendata. How accurately aligned is
>> it? I've noticed that in some places the bing orphophotos match up
>> almost perfectly to the buildings below, and it other areas there can be
>> some difference (sometimes up to a meter of). Taking into account the
>> angle the photo was taken from the air, and ground elevation, which
>> should be considered more accurate?
>>
>
> Neither is perfect.  My own preference is to assume that the OpenData
> stuff is usually more accurately aligned than Bing, which can suffer from
> quite large parallax errors, however it depends on exactly where you are,
> and Bing may sometimes be more accurate.
>
> I believe that the OpenData overlay used for the OSM tiles has not been
> corrected for the known errors between OSGB and WGS84, so is not as good as
> it might be.
>
> If Bing matches buildings on the map, that is because they were mapped
> from the Bing images, without any correction.
>
>
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