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

John F. Eldredge john at jfeldredge.com
Thu Apr 3 21:27:57 UTC 2014


That is my main objection as well.  This proposal is to deliberately reduce the accuracy of the data in the name of saving a few seconds of mapping time.


On April 3, 2014 12:25:46 PM CDT, "Dave F." <davefox at madasafish.com> wrote:
> Mike
> 
> 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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> >
> >
> >
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-- 
John F. Eldredge -- john at jfeldredge.com
"Darkness cannot drive out darkness; only light can do that.  Hate cannot drive out hate; only love can do that."
Dr. Martin Luther King, Jr.



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