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length=

Mike Thompson
I have noticed a "length" tag used on some linear ways [1]. It seems
that this is redundant, as the length could be calculated from the
geometry itself.  It could also be the source of future errors should
someone split the way, for example to add more detailed tagging, such
as varying smoothness.

The length key does have a wiki page [2], but the page doesn't have
much content.  Perhaps it is only intended for nodes?

What do you think?  Should the length tag be used with ways and
relations where the length can be calculated from the geometry itself?
Am I missing something?

MIke

[1] https://www.openstreetmap.org/way/324078614
[2] http://wiki.openstreetmap.org/wiki/Key:length

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Re: length=

François Lacombe-2
Hi Mike,

I don't find it redundant since the length=* tag can give the real length of a feature.
The way in OSM is only a (sometimes not precise) drawing of an existing feature and can be different from the reality.

The wiki can be completed with such a nuance.

I personally recommend to use the length key while mapping street cabinets as nodes.
http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dstreet_cabinet


All the best

François Lacombe

fl dot infosreseaux At gmail dot com
www.infos-reseaux.com
@InfosReseaux

2015-01-27 16:04 GMT+01:00 Mike Thompson <[hidden email]>:
I have noticed a "length" tag used on some linear ways [1]. It seems
that this is redundant, as the length could be calculated from the
geometry itself.  It could also be the source of future errors should
someone split the way, for example to add more detailed tagging, such
as varying smoothness.

The length key does have a wiki page [2], but the page doesn't have
much content.  Perhaps it is only intended for nodes?

What do you think?  Should the length tag be used with ways and
relations where the length can be calculated from the geometry itself?
Am I missing something?

MIke

[1] https://www.openstreetmap.org/way/324078614
[2] http://wiki.openstreetmap.org/wiki/Key:length

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Re: length=

Martin Vonwald (Imagic)


2015-01-27 16:13 GMT+01:00 François Lacombe <[hidden email]>:
I personally recommend to use the length key while mapping street cabinets as nodes.

On a node it makes perfect sense. At least as long as it is not possible/wanted/allowed to provide the geometry.

But on a way? Hm... Any real-world examples for me?

Best regards,
Martin


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Re: length=

Bryan Housel
In reply to this post by Mike Thompson
I just did a quick search in iD.  We display the “Length” field only on the Runway preset.
(I think it does make sense there)

Thanks, Bryan


> On Jan 27, 2015, at 10:04 AM, Mike Thompson <[hidden email]> wrote:
>
> I have noticed a "length" tag used on some linear ways [1]. It seems
> that this is redundant, as the length could be calculated from the
> geometry itself.  It could also be the source of future errors should
> someone split the way, for example to add more detailed tagging, such
> as varying smoothness.
>
> The length key does have a wiki page [2], but the page doesn't have
> much content.  Perhaps it is only intended for nodes?
>
> What do you think?  Should the length tag be used with ways and
> relations where the length can be calculated from the geometry itself?
> Am I missing something?
>
> MIke
>
> [1] https://www.openstreetmap.org/way/324078614
> [2] http://wiki.openstreetmap.org/wiki/Key:length
>
> _______________________________________________
> Tagging mailing list
> [hidden email]
> https://lists.openstreetmap.org/listinfo/tagging


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Re: length=

François Lacombe-2
In reply to this post by Martin Vonwald (Imagic)
2015-01-27 16:18 GMT+01:00 Martin Vonwald <[hidden email]>

But on a way? Hm... Any real-world examples for me?

To be more precise : OSM is based upon a 2D geospatial database.
In my mind, a road climbing a mountain won't have the same length in reality than in the DB : the Z dimension may have influence too.

Dealing with this problem with a length key instead of introducing a 3rd dimension in OSM is dirtier but far more simpler ;)


François Lacombe

fl dot infosreseaux At gmail dot com
www.infos-reseaux.com
@InfosReseaux


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Re: length=

Martin Vonwald (Imagic)
2015-01-27 16:26 GMT+01:00 François Lacombe <[hidden email]>:
In my mind, a road climbing a mountain won't have the same length in reality than in the DB : the Z dimension may have influence too.

Ok - understood. Although I doubt, that there is real usage for that example. But I had a quick look in overpass: besides aeroways it is quite often used on bridges and tunnels, where the actual (official) length can be observed. Makes sense.

Thanks,
Martin

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Re: length=

Michał Brzozowski
Just FYI, at OSM-PL people map highway milestones - as nodes near
highways - which is less prone to error due to people editing
geometry..
The map: http://osmapa.pl/konkursy/pikietaz/

Michał

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Re: length=

Yann Kacenelen
In reply to this post by Mike Thompson
Hi Mike, hi François, hi all,
 
I don't find the "length=*" tag redundant either for linear objects like streetlines, especially in the case of pretty steep ones: as they're projected for mapping purposes from 3D to 2D, their actual length is not the one you measure on the map but you should consider dividing it by cosinus(A) where A is the angle of inclination between the local horizontal plan and the linear feature. Pythagore said it, man ;-)
E.g.: a 17-degree mapped mountain road or San Francisco street's will get its actual length a 5% bonus compared to its real-life counterpart. Pick a 100-meter-or-more road, it's not just a bunch of cm. Depends on the accuracy you need, mostly for analysis purposes.
 
 
My 2c,
 
- Yann
Date: Tue, 27 Jan 2015 16:13:17 +0100
From: François Lacombe <[hidden email]>
To: "Tag discussion, strategy and related tools"
    <[hidden email]>
Subject: Re: [Tagging] length=
Message-ID:
    <[hidden email]>
Content-Type: text/plain; charset="utf-8"

Hi Mike,

I don't find it redundant since the length=* tag can give the real length
of a feature.
The way in OSM is only a (sometimes not precise) drawing of an existing
feature and can be different from the reality.

The wiki can be completed with such a nuance.

I personally recommend to use the length key while mapping street cabinets
as nodes.
http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dstreet_cabinet

All the best

*François Lacombe*

fl dot infosreseaux At gmail dot com
www.infos-reseaux.com
@InfosReseaux <http://www.twitter.com/InfosReseaux>

2015-01-27 16:04 GMT+01:00 Mike Thompson <[hidden email]>:

> I have noticed a "length" tag used on some linear ways [1]. It seems
> that this is redundant, as the length could be calculated from the
> geometry itself.  It could also be the source of future errors should
> someone split the way, for example to add more detailed tagging, such
> as varying smoothness.
>
> The length key does have a wiki page [2], but the page doesn't have
> much content.  Perhaps it is only intended for nodes?
>
> What do you think?  Should the length tag be used with ways and
> relations where the length can be calculated from the geometry itself?
> Am I missing something?
>
> MIke
>
> [1] https://www.openstreetmap.org/way/324078614
> [2] http://wiki.openstreetmap.org/wiki/Key:length
>

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Re: length=

fly high
In reply to this post by Martin Vonwald (Imagic)
Am 27.01.2015 um 16:34 schrieb Martin Vonwald:

> 2015-01-27 16:26 GMT+01:00 François Lacombe <[hidden email]
> <mailto:[hidden email]>>:
>
>     In my mind, a road climbing a mountain won't have the same length in
>     reality than in the DB : the Z dimension may have influence too.
>
>
> Ok - understood. Although I doubt, that there is real usage for that
> example. But I had a quick look in overpass: besides aeroways it is
> quite often used on bridges and tunnels, where the actual (official)
> length can be observed. Makes sense.

But how to handle it one ways considering splitting and combining ways ?

For bridges and tunnels this info belongs to the area or the relation
but not to an unclosed linear way.

About aeroways we already have an own thread as we have more problems
with them.

cu fly




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Re: length=

Mike Thompson
In reply to this post by Michał Brzozowski
Thanks to everyone for sharing their thoughts.

> I personally recommend to use the length key while mapping street cabinets as nodes.

Agree, length makes sense on nodes


> The way in OSM is only a (sometimes not precise) drawing of an existing feature and can be different from the reality.

How precise is the value of the "length" tag? From what is the value derived?


> To be more precise : OSM is based upon a 2D geospatial database.
In my mind, a road climbing a mountain won't have the same length in
reality than in the DB : the Z dimension may have influence too.

For most highways this will have little difference.  10% (10 vertical
meters per 100 horizontal meters) is considered a steep highway grade.
In this example, the actual road length will be 100.5 meters
(sqrt(10^2 + 100^2)). For ski slopes and aerial trams, yes, it will
have a larger influence.


> it is quite often used on bridges and tunnels, where the actual (official) length can be observed.

Perhaps "official_length" or "signed_length" might be more indicative
of what actually is being recorded.

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Re: length=

Mike Thompson
In reply to this post by Yann Kacenelen
> E.g.: a 17-degree mapped mountain road or San Francisco street's will get
> its actual length a 5% bonus compared to its real-life counterpart.

True, but such roads are not very common (17 degree ~= 30%). There are
a few short streets in places like San Francisco that are this steep.
In these cases if someone actually went out and measured them with
suitably precise equipment it might make sense to have some sort of
length tag, but I would suggest something to differentiate it from a
purely horizontal measurement. Of course, you could also drape the OSM
data over a suitably detailed DEM (digital elevation model) to get
your answer as well.



> Depends on the accuracy
> you need, mostly for analysis purposes.

If you need that level of accuracy you may want to consider data
sources in addition to OSM.

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Re: length=

Brad Neuhauser
In reply to this post by Michał Brzozowski
Quick note: for milestones, the tag used is distance, not length. There's a wiki page with all unit tags if you're into that sort of thing: http://wiki.openstreetmap.org/wiki/Map_Features/Units

On Tue, Jan 27, 2015 at 9:40 AM, Michał Brzozowski <[hidden email]> wrote:
Just FYI, at OSM-PL people map highway milestones - as nodes near
highways - which is less prone to error due to people editing
geometry..
The map: http://osmapa.pl/konkursy/pikietaz/

Michał

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Re: length=

moltonel 3x Combo
In reply to this post by Mike Thompson
On 27/01/2015, Mike Thompson <[hidden email]> wrote:
>> The way in OSM is only a (sometimes not precise) drawing of an existing
>> feature and can be different from the reality.
>
> How precise is the value of the "length" tag? From what is the value
> derived?

In my experience of hiking trails in Ireland, the length advertised
on-site and in leaflets is often 10-20% off (as measured by my treking
GPS that takes relief into account). I expect OSM + SRTM to be more
precise. YMMV of course.

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Re: length=

Eric Sibert
In reply to this post by Martin Vonwald (Imagic)
Le 27/01/2015 16:34, Martin Vonwald a écrit :
> Ok - understood. Although I doubt, that there is real usage for that
> example. But I had a quick look in overpass: besides aeroways it is
> quite often used on bridges and tunnels, where the actual (official)
> length can be observed. Makes sense.

Indeed, for tunnels, I just put the length indicated at the entrance in
note=*...
... and some other contributors transfered it to length=*.

Eric


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Re: length=

Warin
In reply to this post by Mike Thompson
On 28/01/2015 3:26 AM, Mike Thompson wrote:

>> E.g.: a 17-degree mapped mountain road or San Francisco street's will get
>> its actual length a 5% bonus compared to its real-life counterpart.
> True, but such roads are not very common (17 degree ~= 30%). There are
> a few short streets in places like San Francisco that are this steep.
> In these cases if someone actually went out and measured them with
> suitably precise equipment it might make sense to have some sort of
> length tag, but I would suggest something to differentiate it from a
> purely horizontal measurement. Of course, you could also drape the OSM
> data over a suitably detailed DEM (digital elevation model) to get
> your answer as well.
>
>

Or you could tag the slope/gradient of the road .. I've tagged a short
section of my street at 17% .. that is averaged .. it peaks at 23%. You
can then use that to work out the travelled distance, height gained/lost
etc.

As for tracks being out by uptp 20% .. that is faily normal expection on
outback roads .. they are dirt and if the grader driver (or his boss,
the local farmer etc) think it would be better off over there .,. then
that is where it goes .. can add some distance to what is on the map or
road sign. I've come across a road that was realigned in such a manner
for over 100 miles.

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Re: length=

Florian Lohoff-2
In reply to this post by Martin Vonwald (Imagic)
On Tue, Jan 27, 2015 at 04:18:57PM +0100, Martin Vonwald wrote:
> 2015-01-27 16:13 GMT+01:00 François Lacombe <[hidden email]>:
>
> > I personally recommend to use the length key while mapping street cabinets
> > as nodes.
> > <http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dstreet_cabinet>
>
> On a node it makes perfect sense. At least as long as it is not
> possible/wanted/allowed to provide the geometry.

Does it ? I cant think of any application where this makes sense.
A node does not have an orientation so why can it have a length?

If it has a length it does not make sense to use a node.

Flo
--
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Re: length=

François Lacombe-2
2015-01-28 8:58 GMT+01:00 Florian Lohoff <[hidden email]>:

Does it ? I cant think of any application where this makes sense.
A node does not have an orientation so why can it have a length?

If it has a length it does not make sense to use a node.

Flo

Since OSM editing tools aren't AutoCAD you can't be 100% precise on the geometry.
Some small features can actually be summarized as nodes when drawing their shape sounds irrelevant regarding the cluttering it introduces.

I'm sorry that was trivial for me.
I won't draw a circle for a 5cm diameter pole and so on...

That's why tags are intended for several kind of primitives instead of only one sometimes.


François Lacombe

fl dot infosreseaux At gmail dot com
www.infos-reseaux.com
@InfosReseaux


 
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Re: length=

Martin Vonwald (Imagic)
In reply to this post by Florian Lohoff-2


2015-01-28 8:58 GMT+01:00 Florian Lohoff <[hidden email]>:
On Tue, Jan 27, 2015 at 04:18:57PM +0100, Martin Vonwald wrote:
> 2015-01-27 16:13 GMT+01:00 François Lacombe <[hidden email]>:
>
> > I personally recommend to use the length key while mapping street cabinets
> > as nodes.
> > <http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dstreet_cabinet>
>
> On a node it makes perfect sense. At least as long as it is not
> possible/wanted/allowed to provide the geometry.

Does it ? I cant think of any application where this makes sense.
A node does not have an orientation so why can it have a length?

If it has a length it does not make sense to use a node.

Read my second sentence again. Some mappers do not want to draw geometry for some small feature. See e.g. man_made=street_cabinet. There you have a length and width. Together with the key direction one can determine the geometry. I don't see why anyone would want to do it that way instead of simply drawing a box, but I accept the fact, that some users do, so it's fine for me.

Best regards,
Martin


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Re: length=

François Lacombe-2
2015-01-28 9:14 GMT+01:00 Martin Vonwald <[hidden email]>:
 I don't see why anyone would want to do it that way instead of simply drawing a box, but I accept the fact, that some users do, so it's fine for me.

It's more precise to use tools like compass or meters to get the cabinet's (or any other small feature) dimensions and put in tags value instead of drawing a box.
Drawing a box isn't really precise and there will be a kind of data loss.

It's only a scale matter and such thought only apply to prismatic shapes.

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Re: length=

dieterdreist
In reply to this post by Mike Thompson

2015-01-27 17:13 GMT+01:00 Mike Thompson <[hidden email]>:
> The way in OSM is only a (sometimes not precise) drawing of an existing feature and can be different from the reality.

How precise is the value of the "length" tag? From what is the value derived?



to make sense on ways, I'd expect it to represent either a measurement in the real world (e.g. with tape) or the indication you can get from a sign (e.g. length of a bridge). Measuring e.g. in JOSM or GIS from the cartography or from imagery or calculating it from the coords does not make sense (but I doubt people do it like this).

cheers,
Martin

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