[Tagging] simple_brunnel : one node bridge like xing highway over waterway
miketho16 at gmail.com
Wed Apr 2 17:40:01 UTC 2014
> 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.
A bridge that is a single node could also have a tag for length (as well as
one for width). I am not suggesting this, just pointing out that tags
could be added to other geometries to denote additional dimensions. The
point is we have chosen to use geometry that does not have width to
represent a real world object that does. Also, in many cases the width tag
is is not used on roads.
On Wed, Apr 2, 2014 at 11:29 AM, Mike Thompson <miketho16 at gmail.com> 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> wrote:
>> 2014-04-02 18:16 GMT+02:00 Mike Thompson <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 ;-)
>> Tagging mailing list
>> Tagging at openstreetmap.org
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