[Tagging] simple_brunnel : one node bridge like xing highway over waterway

Dave F. davefox at madasafish.com
Thu Apr 3 17:25:46 UTC 2014


We should be mapping as accurately as we can within the limitations (gps 
accuracy, aerial imagery etc) that we have. Data can always be upgraded 
when more accurate information becomes available. This proposal is a 
step backwards towards inaccuracy.

On 02/04/2014 18:29, Mike Thompson wrote:

> > We aim at precision/accuracy (IMHO, at least I do),
> 1) How much precision/accuracy?  No real world measurement or 
> recording of such measurement is exactly precise/accurate. Do you use 
> a commercial grade differential GPS when surveying?  When you are 
> create a way to represent a road which in reality is an arc or curve, 
> how many nodes do you use?  You could increase your precision by 
> adding more nodes.
> 2) In general, there is a cost to increased precision (and accuracy) 
> in terms of the survey effort, the survey equipment, the recording 
> effort, and the computing resources.
> 3) At some point the value of increased precision ceases to grow, and 
> may even decline.

> On Wed, Apr 2, 2014 at 10:33 AM, Martin Koppenhoefer 
> <dieterdreist at gmail.com <mailto:dieterdreist at gmail.com>> wrote:
>     2014-04-02 18:16 GMT+02:00 Mike Thompson <miketho16 at gmail.com
>     <mailto:miketho16 at gmail.com>>:
>         > It is also a significant loss of detail because you reduce
>         the length of the bridge to 0
>         Maps are abstractions. They don't represent reality precisely.
>     We aim at precision/accuracy (IMHO, at least I do), you can always
>     create more abstracted maps from precise geodata, while the other
>     way round it is not possible.
>           In most cases we already reduce the width of roads to 0 as
>         they are not represented by areas.
>     no, their geometric representation is a line, but their width is
>     (or can be) added with a tag like width and lanes, of which the
>     latter defaults to 2 (for non-links) if not added explicitly.
>          The question should be whether the value of the data is
>         significantly degraded if some very short bridges are
>         represented as nodes.
>     OK. Can you explain how long a "very short bridge" should be? What
>     is the benefit of this kind of mapping style?
>     In this context I'd like to point out that GPS precision is not
>     the limit, you do not have to take 2 waypoints at the beginning
>     and end of the bridge and the result will become your bridge,
>     automatically, usually you will interpret these waypoints and will
>     estimate the bridge length and represent it according to your
>     estimate, so I do not think a 3 meters long bridge will result in
>     a 45 meters long zigzag in your mapping, just because you had bad
>     GPS reception under the tree canopy and made a break on the bridge ;-)
>     cheers,
>     Martin
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