[talk-au] maxheight/height

[John Smith]

I've noticed some people have tagged bridges with height=*, rather than tagging 
the road way under the bridge as maxheight=* and I'm kind of unsure which is 
better.

By using height you don't have to break the way under the bridge up, on the 
other hand maxheight is specific to the road under the bridge.

That all said I think height was a predecessor tag to ele and then again I've 
seen trees tagged with a height too.


  

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Mon, Jul 27, 2009 at 6:57 PM, John Smith  wrote:
>
> I've noticed some people have tagged bridges with height=*, rather than 
> tagging the road way under the bridge as maxheight=* and I'm kind of unsure 
> which is better.

I think the bridge should be tagged.

Firstly, height is an attribute of the bridge, not of the road under the bridge.

Secondly, if you were to tag the "road way under the bridge", there is
actually only an infinitesimally small length of road "under" the
bridge, because the bridge is a way with - by definition - zero width.

Thirdly, I have heard some argue that tagging the "road way under the
bridge" would be more convenient for routing. But I think tagging for
the router in this way should be discouraged, just as tagging for the
renderer is.

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Re: [talk-au] maxheight/height

[John Smith]

--- On Mon, 27/7/09, Roy Wallace  wrote:

> I think the bridge should be tagged.

There was an overwhelming response on the main talk list that this be tagged as 
maxheight on the way that has the restriction, ie you can't go under the bridge 
unless you are under x metres.

height on the other hand is used to indicate the maximum height of the bridge 
which usually exceeds the clearance for something going under the bridge.

An example given was a suspension bridge, the clearance for boats is less than 
the height the piers extend above the water.


  

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Mon, Jul 27, 2009 at 9:47 PM, John Smith wrote:
> --- On Mon, 27/7/09, Roy Wallace  wrote:
>
>> I think the bridge should be tagged.
>
> There was an overwhelming response on the main talk list that this be tagged 
> as maxheight on the way that has the restriction, ie you can't go under the 
> bridge unless you are under x metres.

There are two issues here: 1) what should be tagged and 2) what should
it be tagged with.

For 1), what should be tagged? Definitely the bridge. For two reasons:
firstly, clearance under a bridge is an attribute of the bridge.
Secondly, it is not possible to refer to "the section of the way that
is under the bridge", because the bridge is a way with zero width. The
only alternative is to tag "the entire length of any way that goes
under the bridge" or "some arbitrary length of any way that goes under
the bridge". I think these alternatives are undesirable at best -
misleading and messy at worst. For example, it's kind of like tagging
any house that's next to a park as "next_to_a_park=yes", rather than
tagging the big grassy area as "leisure=park" (yes, this is an
exaggeration, but the analogy is tagging the thing that is affected by
something rather than tagging the something itself).

For 2), what should it be tagged with? I concede that a bridge tagged
with "height" could be misinterpreted (as the actual height of the
bridge or bridge construction), as could "maxheight" (as referring to
a restriction involved with traveling on top of the bridge).

Therefore, I suggest a new tag, "clearance". A new tag should be
created when the current tags do not describe things adequately, which
I think is what has happened in this case.

Thoughts?

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Re: [talk-au] maxheight/height

[Stephen Hope]

No, you're wrong here. Maxheight is an element of the way that goes
under the bridge.  It is caused by the bridge, but it is not part of
the bridge.  It is the road under the bridge that has the limitation,
not the bridge. Divided roads often have different max heights on each
side, but it is one level bridge over the top.

Max-height can be caused by overhanging trees, low wires, odd road
signs that stick out over the road, even buildings or roadside rocks
that bulge out over the road. Whatever the cause, it is the road
itself that is affected, and should be tagged.  On a motorway, the max
height section can be several km long - the distance between exits,
and it is all covered by the same limitation, legally. On other roads
it may be only a few meters, and could be covered by a node tag.

Stephen


2009/7/28 Roy Wallace :
>
> For 1), what should be tagged? Definitely the bridge. For two reasons:
> firstly, clearance under a bridge is an attribute of the bridge.
> Secondly, it is not possible to refer to "the section of the way that
> is under the bridge", because the bridge is a way with zero width. The
> only alternative is to tag "the entire length of any way that goes
> under the bridge" or "some arbitrary length of any way that goes under
> the bridge". I think these alternatives are undesirable at best -
> misleading and messy at worst. For example, it's kind of like tagging
> any house that's next to a park as "next_to_a_park=yes", rather than
> tagging the big grassy area as "leisure=park" (yes, this is an
> exaggeration, but the analogy is tagging the thing that is affected by
> something rather than tagging the something itself).
>

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Re: [talk-au] maxheight/height

[Cameron]

I think tag the part of the way that is signed. Generally before bridges
there is a sign informing road users of the bridge's restrictions. Sometimes
they will offer an alternate route for larger vehicles. So tag from the
nearest junction if available or the sign.

A clearance tag could just as easily be misinterpreted as the maxheight tag.

~Cameron


2009/7/28 Roy Wallace 

> On Mon, Jul 27, 2009 at 9:47 PM, John Smith
> wrote:
> > --- On Mon, 27/7/09, Roy Wallace  wrote:
> >
> >> I think the bridge should be tagged.
> >
> > There was an overwhelming response on the main talk list that this be
> tagged as maxheight on the way that has the restriction, ie you can't go
> under the bridge unless you are under x metres.
>
> There are two issues here: 1) what should be tagged and 2) what should
> it be tagged with.
>
> For 1), what should be tagged? Definitely the bridge. For two reasons:
> firstly, clearance under a bridge is an attribute of the bridge.
> Secondly, it is not possible to refer to "the section of the way that
> is under the bridge", because the bridge is a way with zero width. The
> only alternative is to tag "the entire length of any way that goes
> under the bridge" or "some arbitrary length of any way that goes under
> the bridge". I think these alternatives are undesirable at best -
> misleading and messy at worst. For example, it's kind of like tagging
> any house that's next to a park as "next_to_a_park=yes", rather than
> tagging the big grassy area as "leisure=park" (yes, this is an
> exaggeration, but the analogy is tagging the thing that is affected by
> something rather than tagging the something itself).
>
> For 2), what should it be tagged with? I concede that a bridge tagged
> with "height" could be misinterpreted (as the actual height of the
> bridge or bridge construction), as could "maxheight" (as referring to
> a restriction involved with traveling on top of the bridge).
>
> Therefore, I suggest a new tag, "clearance". A new tag should be
> created when the current tags do not describe things adequately, which
> I think is what has happened in this case.
>
> Thoughts?
>
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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 10:10 AM, Stephen Hope wrote:
> No, you're wrong here. Maxheight is an element of the way that goes
> under the bridge.  It is caused by the bridge, but it is not part of
> the bridge.

You're saying that the clearance under a bridge is not an attribute of
the bridge? I'm not at all convinced of that. But it is subjective, so
we may have to agree to disagree.

> It is the road under the bridge that has the limitation,
> not the bridge. Divided roads often have different max heights on each
> side, but it is one level bridge over the top.

Good point, though I would suspect this is relatively rare (i.e. I've
never seen this).

> Max-height can be caused by overhanging trees, low wires, odd road
> signs that stick out over the road, even buildings or roadside rocks
> that bulge out over the road. Whatever the cause, it is the road
> itself that is affected, and should be tagged.

I disagree. We should be tagging "things", not tagging the "effect of things".

> On a motorway, the max
> height section can be several km long - the distance between exits,
> and it is all covered by the same limitation, legally. On other roads
> it may be only a few meters, and could be covered by a node tag.

Sounds like a maintenance nightmare. I'm also not sure that a
"clearance" under a bridge is equivalent to a "legal limitation" for
the section of motorway between the exits before and after the bridge,
as you say. And what if a motorway and bridge are tagged, but exits
are missing, etc. Just sounds a lot harder to maintain than tagging
the bridge itself.

Can you explain what you mean by "may be only a few meters", and
"could be covered by a node tag"? If you can specify an exact
preferred way of tagging this (and document it on the wiki), I may
well be convinced.

Cheers,
Roy

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 10:15 AM,
Cameron wrote:
> I think tag the part of the way that is signed. Generally before bridges
> there is a sign informing road users of the bridge's restrictions. Sometimes
> they will offer an alternate route for larger vehicles. So tag from the
> nearest junction if available or the sign.

Funnily enough, where I have been mapping the sign is always on the
bridge itself. Anyway, I think we should be tagging what the sign is
referring to, independent of the sign itself.

> A clearance tag could just as easily be misinterpreted as the maxheight tag.

I don't see how. "bridge=yes; clearance=2.8"...

Roy

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Re: [talk-au] maxheight/height

[Liz]

On Tue, 28 Jul 2009, Roy Wallace wrote:
> On Tue, Jul 28, 2009 at 10:10 AM, Stephen Hope wrote:
> > No, you're wrong here. Maxheight is an element of the way that goes
> > under the bridge.  It is caused by the bridge, but it is not part of
> > the bridge.
>
> You're saying that the clearance under a bridge is not an attribute of
> the bridge? I'm not at all convinced of that. But it is subjective, so
> we may have to agree to disagree.
>
> > It is the road under the bridge that has the limitation,
> > not the bridge. Divided roads often have different max heights on each
> > side, but it is one level bridge over the top.
>

snip

we're arguing about matters regarding the logic of choices (as usual)

then the logic of the name applied to the choice, which gets into 
philosophical arguments which remind me of Plato. 
http://en.wikipedia.org/wiki/Plato

The problem is that at a time in the past a decision was made (Principle A) 
whose logic is now questioned.
A lot has been uploaded onto the server using "Principle A", which will have 
to be reworked if "Principle B" succeeds "Principle A".
So regardless of the logic, people will support "Principle A"  because of the 
work involved in change.
Just look at the work involved by the API change from 0.5 to 0.6


To return to the bridge
the following attributes of the bridge and the road underneath it all need to 
be considered 
Height of bridge
Height above sea level of the bridge
Max height of the arch of the bridge above the roadway
Max height of a vehicle which can drive under the bridge, which if the bridge 
is an arch must be less than the max height of the arch 
Max height of a vehicle which the engineer said was permitted to drive under 
the bridge

so now I have 5 "height" measures
some of which belong to the road and some to the bridge, and some to both.

then we need unambiguous tags to refer to these 5 concepts and translations of 
them all.
:-)







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Re: [talk-au] maxheight/height

[Ross Scanlon]

On Tue, 28 Jul 2009 10:34:00 +1000
Roy Wallace  wrote:

> 
> > A clearance tag could just as easily be misinterpreted as the maxheight tag.
> 
> I don't see how. "bridge=yes; clearance=2.8"...
> 
> Roy

Does this mean the bridge has a clearance of 2.8 or the road under the bridge 
has a clearance of 2.8.  To me this would suggest the bridge has a limit of 2.8 
ie vehicles travelling over the bridge can not be above 2.8 high.

I'd suggest that if the bridge has a height limit, ie clearance, then the 
bridge is tagged with max_height.

If the road under the bridge has a height limit, ie clearance, then the road is 
tagged.

Box bridges have height limits. Roads that pass under a bridge generally have 
height limits.

-- 
Cheers
Ross

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Re: [talk-au] [OSM-talk] maxheight/height

[Liz]

On Tue, 28 Jul 2009, Dirk-Lüder Kreie wrote:
> Liz schrieb:
> > To return to the bridge
> > the following attributes of the bridge and the road underneath it all
> > need to be considered
> > Height of bridge
> > Height above sea level of the bridge
> > Max height of the arch of the bridge above the roadway
> > Max height of a vehicle which can drive under the bridge, which if the
> > bridge is an arch must be less than the max height of the arch
> > Max height of a vehicle which the engineer said was permitted to drive
> > under the bridge
> >
> > so now I have 5 "height" measures
> > some of which belong to the road and some to the bridge, and some to
> > both.
> >
> > then we need unambiguous tags to refer to these 5 concepts and
> > translations of them all.
> >
> > :-)
>
> What about a max height of vehicles passing over the bridge? there are
> quite a lot of bridges which have support structures limiting he height
> of vehicles passing over it.
> how do you distinguish this, and how do you make it clear to every
> mapper what is what?
I'm happy to admit I've missed a 6th height measure
- missing possible scenarios is one of our problems in tagging.

This just came up on the talk_au where this discussion is running in parallel


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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 11:04 AM, Ross Scanlon wrote:
> Does this mean the bridge has a clearance of 2.8 or the road under the bridge 
> has a clearance of 2.8.  To me this would suggest the bridge has a limit of 
> 2.8 ie vehicles travelling over the bridge can not be above 2.8 high.
>
> I'd suggest that if the bridge has a height limit, ie clearance, then the 
> bridge is tagged with max_height.
>
> If the road under the bridge has a height limit, ie clearance, then the road 
> is tagged.

Sorry, maybe this is a language issue. In my mind, "height limit" of a
way refers to maximum height *above* the way, whereas "clearance" of a
way infers maximum height *under* the way. Maybe "clearance" isn't the
best word for this - please suggest others.

My main point is that when there is a "maximum height under a way",
this should be tagged as an attribute of that way, not of the ways
that pass under it.

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Re: [talk-au] [OSM-talk] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 11:14 AM, Apollinaris Schoell wrote:
>  one bridge can cross multiple roads with different maxheight limtations.

This is a good argument in favour of tagging the ways that pass under
a bridge instead of the bridge. But I think it should be weighed
against the arguments for the other method.

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Re: [talk-au] [OSM-talk] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 11:14 AM, Apollinaris Schoell wrote:
>  one bridge can cross multiple roads with different maxheight limtations.

And, by the way, on the other hand: one way can pass under multiple
bridges with different clearances. I'd actually suggest this scenario
is more common.

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Re: [talk-au] maxheight/height

[Liz]

On Tue, 28 Jul 2009, Roy Wallace wrote:
> My main point is that when there is a "maximum height under a way",
> this should be tagged as an attribute of that way, not of the ways
> that pass under it.

Here I cannot agree
When I travel over the bridge I am not interested in the maximum height of the 
way which travels under the bridge.

When I travel under the bridge I am interested in the height limitation.

Going back to my multipart specification, trying to really comprehend the 
logic

the height of the arch is a property of the bridge.
the max height which can go under the bridge is a property of the way / node 
beneath it

note that counter-intuitively, height > max height > clearance

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[talk-au] multiple use of nodes

[Liz]

I have been using nodes for more than one thing, and it isn't supported.
So I have been re-using the Post Office node for the town name node, and then 
the town names don't render.
Some of these have been tracked down by other mappers, but I'd be happy to 
have anyone fix up any more I've done across 5 States.

(and its taken me 18 months to figure out this problem)


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Re: [talk-au] multiple use of nodes

[John Smith]

--- On Mon, 27/7/09, Liz  wrote:

> I'd be happy to 
> have anyone fix up any more I've done across 5 States.

I can whip up a simple page showing you all nodes that have multiple things, I 
just need an idea of what you used, like the place=* and amenity=* for example.


  

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Re: [talk-au] maxheight/height

[John Smith]

I think everyone is thinking of this in one of 2 ways, it's either an attribute 
of the bridge, or a restriction of the way under the bridge.

The maxheight tag looks like it was aimed as a restriction tag, the way below 
the bridge is restricted if you are above or close to X metres you will need to 
travel another path.

I think adding a clearance tag will only serve to confuse things even further 
and I don't think we need to be redundant here.

Also I've seen different sides of a bridge signed as different clearances when 
bridges slope and one side is lower than the other side.

As for using a node to indicate maxheight, this seems to me to be a very clean 
way of dealing with it, since any routing software would only need one obstacle 
to reject that section of way and find another path.


  

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Re: [talk-au] multiple use of nodes

[Elizabeth Dodd]

On Tue, 28 Jul 2009, John Smith wrote:
> > I'd be happy to
> > have anyone fix up any more I've done across 5 States.
>
> I can whip up a simple page showing you all nodes that have multiple
> things, I just need an idea of what you used, like the place=* and
> amenity=* for example.
>
>
>  
I've just found amenity=fuel place=village name=Stockinbingal
where the general store sells fuel, is the post office and so on


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Re: [talk-au] multiple use of nodes

[John Smith]

--- On Mon, 27/7/09, Elizabeth Dodd  wrote:

> I've just found amenity=fuel place=village
> name=Stockinbingal
> where the general store sells fuel, is the post office and
> so on

There is a lot of nodes tagged with amenity=* and place=* and some of the place 
tags are empty.

http://maps.bigtincan.com/tagwatch/seek.php

The page may take 20-30s to load if the query cache has emptied due to updates, 
either from people refreshing data manually from OSM or the automatic updates 
that happen every 15 minutes.


  

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Re: [talk-au] multiple use of nodes

[Elizabeth Dodd]

On Tue, 28 Jul 2009, John Smith wrote:
> There is a lot of nodes tagged with amenity=* and place=* and some of the
> place tags are empty.
>
> http://maps.bigtincan.com/tagwatch/seek.php
>
> The page may take 20-30s to load if the query cache has emptied due to
> updates, either from people refreshing data manually from OSM or the
> automatic updates that happen every 15 minutes.
Way: McDonalds (448169168)
Tags:   
amenity = fast_food
historic =
name = McDonalds
place =
tourism = 
the empty tags don't show in potlatch but they do in Josm
so those empty tags i deleted




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Re: [talk-au] multiple use of nodes

[John Smith]

--- On Mon, 27/7/09, Elizabeth Dodd  wrote:
> the empty tags don't show in potlatch but they do in Josm
> so those empty tags i deleted

I noticed that yesterday I have no idea what potlatch does with empty tags, 
maybe they are automatically deleted if you make a change?


  

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Re: [talk-au] multiple use of nodes

[John Smith]

Yup, if you make a change in potlatch any empty tags aren't saved...


  

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Re: [talk-au] multiple use of nodes

[John Smith]

Does anyone else know of any other tag combinations worth searching for?


  

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Re: [talk-au] multiple use of nodes

[Liz]

On Tue, 28 Jul 2009, John Smith wrote:
> Does anyone else know of any other tag combinations worth searching for?

that's because we've fixed them all up
:-)


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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 11:33 AM, Liz wrote:
> When I travel over the bridge I am not interested in the maximum height of the
> way which travels under the bridge.
>
> When I travel under the bridge I am interested in the height limitation.

Ah, perhaps our difference in opinion stems from our different
perspectives - your emphasis on "when I travel" vs my emphasis on,
perhaps, "when I look at a map", or "when I conceptualise the world".

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Re: [talk-au] multiple use of nodes

[John Smith]

--- On Tue, 28/7/09, Liz  wrote:

> that's because we've fixed them all up
> :-)

Yes for places + amenities, but I meant other combinations that may be valid 
but won't render, like (thinks randomly) places + sport


  

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 12:26 PM, John Smith wrote:
>
> I think everyone is thinking of this in one of 2 ways, it's either an 
> attribute of the bridge, or a restriction of the way under the bridge.

Agreed. And it's clear that both ways of thinking are probably valid.

> As for using a node to indicate maxheight, this seems to me to be a very 
> clean way of dealing with it, since any routing software would only need one 
> obstacle to reject that section of way and find another path.

Can you please explain exactly what you mean by "using a node to
indicate maxheight"? This seems to be different from the posts which
seemed to suggest tagging, e.g. sections of motorway between exits,
etc. Like I said, my main argument for tagging the bridge is that it's
unambiguous and easy to implement and maintain.

If you have a consistent scheme for tagging the ways which pass under
bridges, which is unambiguous and easy to implement and maintain,
please share and document on the wiki :)

Cheers,
Roy

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Re: [talk-au] multiple use of nodes

[John Smith]

I updated the seek code to place + sport and well yea...


  

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Re: [talk-au] multiple use of nodes

[John Smith]

I updated the seek code to place + sport and well yea...

http://maps.bigtincan.com/tagwatch/seek.php


  

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Re: [talk-au] maxheight/height

[John Smith]

--- On Tue, 28/7/09, Roy Wallace  wrote:

> Agreed. And it's clear that both ways of thinking are
> probably valid.

As of time of writing maxheight is the only valid one and I don't think we need 
or should have 2 tags to indicate the same thing in 2 different ways.

> Can you please explain exactly what you mean by "using a
> node to
> indicate maxheight"? This seems to be different from the

Someone posted about this earlier, have a node on the way effected, near or 
under the bridge, rather than splitting the way and then tagging that node as 
maxheight or clearence might be the better option that making a new section of 
way. However maxheight is currently only applicable to ways not nodes.

> posts which
> seemed to suggest tagging, e.g. sections of motorway
> between exits,
> etc. Like I said, my main argument for tagging the bridge
> is that it's
> unambiguous and easy to implement and maintain.

It's not hard or ambiguous, it just means splitting a way under the bridge 
similar to splitting a bridge.

> If you have a consistent scheme for tagging the ways which
> pass under
> bridges, which is unambiguous and easy to implement and
> maintain,
> please share and document on the wiki :)

It's a little more complicated then that, at present there was agreement on 
maxheight as a restriction tag and that is perfectly valid as far as I'm 
concerned.


  

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Re: [talk-au] [OSM-talk] maxheight/height

[Liz]

On Tue, 28 Jul 2009, Roy Wallace wrote:
> On Tue, Jul 28, 2009 at 12:26 PM, John Smith wrote:
> > I think everyone is thinking of this in one of 2 ways, it's either an
> > attribute of the bridge, or a restriction of the way under the bridge.
>
> Agreed. And it's clear that both ways of thinking are probably valid.
>
> > As for using a node to indicate maxheight, this seems to me to be a very
> > clean way of dealing with it, since any routing software would only need
> > one obstacle to reject that section of way and find another path.
>
> Can you please explain exactly what you mean by "using a node to
> indicate maxheight"? This seems to be different from the posts which
> seemed to suggest tagging, e.g. sections of motorway between exits,
> etc. Like I said, my main argument for tagging the bridge is that it's
> unambiguous and easy to implement and maintain.
>
> If you have a consistent scheme for tagging the ways which pass under
> bridges, which is unambiguous and easy to implement and maintain,
> please share and document on the wiki :)
>
> Cheers,
> Roy
>
I don't think that we have a consistent clear unambiguous easily_maintained 
and implemented system yet.
It certainly isn't up to "document on the wiki" standard.
But a few more posts from all comers and we could be close to 'clear' and 
'unambiguous'.


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Re: [talk-au] maxheight/height

[John Smith]

--- On Tue, 28/7/09, Roy Wallace  wrote:

> Ah, perhaps our difference in opinion stems from our
> different
> perspectives - your emphasis on "when I travel" vs my
> emphasis on,
> perhaps, "when I look at a map", or "when I conceptualise
> the world".

That was the basis of the 2 sets of logic, one is a restriction, the other is a 
physical attribute. maxheight is a restriction so belongs attached to the way 
that would be restricted.


  

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Re: [talk-au] multiple use of nodes

[John Smith]

> I updated the seek code to place + sport and well yea...

Actually they all seem to be valid, named dive spots, so that example was wrong 
:)


  

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 2:57 PM, John Smith wrote:
> As of time of writing maxheight is the only valid one and I don't think we 
> need or should have 2 tags to indicate the
same thing in 2 different ways.

I meant there's two ways of conceptualising the distance below a
bridge (as an "attribute" or a "restriction"). I'm not suggesting we
need 2 different tags. I'm quite happy to tag it as a "restriction",
if we can agree on how it should be implemented.

> have a node on the way effected, near or under the bridge, rather than 
> splitting the way and then tagging that node as maxheight or clearence might 
> be the better option that making a new section of way. However maxheight is 
> currently only applicable to ways not nodes.
> ... It's not hard or ambiguous, it just means splitting a way under the 
> bridge similar to splitting a bridge.

I would at least suggest that - if maxheight is applied to a node, as
you suggest - the node should be *shared* by the bridge (way) and the
way passing under. This makes it clearer that maxheight is
specifically referring to the bridge clearance. Also, if someone is
checking, for example, whether maxheight is specified for a particular
bridge/way, they don't have to go searching for some random node
"near" the bridge.

By the way, you can't place a node "under the bridge", unless it is
indeed shared by the bridge, as all ways have zero width (right?).

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Re: [talk-au] maxheight/height

[John Smith]

--- On Tue, 28/7/09, Roy Wallace  wrote:

> I would at least suggest that - if maxheight is applied to
> a node, as
> you suggest - the node should be *shared* by the bridge
> (way) and the
> way passing under. This makes it clearer that maxheight is

The problem with this is that 2 ways sharing a node are physically connected 
and this wouldn't be the case as one passes over the other.

> specifically referring to the bridge clearance. Also, if
> someone is
> checking, for example, whether maxheight is specified for a
> particular
> bridge/way, they don't have to go searching for some random
> node
> "near" the bridge.

Searching for a node near the bridge would be easier than searching for a way 
since the node would be in close proximity to the bridge and you search by 
lat/lon rather than random nodes.

> By the way, you can't place a node "under the bridge",
> unless it is
> indeed shared by the bridge, as all ways have zero width
> (right?).

You can use the maxwidth tag to indicate the maximum width and object must be 
to pass a restriction on the way, like an underpass of a bridge :)


  

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Re: [talk-au] maxheight/height

[Liz]

On Tue, 28 Jul 2009, Roy Wallace wrote:
> By the way, you can't place a node "under the bridge", unless it is
> indeed shared by the bridge, as all ways have zero width (right?).

Logically you can as they are on different layers.


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Re: [talk-au] maxheight/height

[Ross Scanlon]

On Tue, 28 Jul 2009 15:24:35 +1000
Roy Wallace  wrote:

> > have a node on the way effected, near or under the bridge, rather than 
> > splitting the way and then tagging that node as maxheight or clearence 
> > might be the better option that making a new section of way. However 
> > maxheight is currently only applicable to ways not nodes.
> > ... It's not hard or ambiguous, it just means splitting a way under the 
> > bridge similar to splitting a bridge.
 
> I would at least suggest that - if maxheight is applied to a node, as
> you suggest - the node should be *shared* by the bridge (way) and the
> way passing under. This makes it clearer that maxheight is
> specifically referring to the bridge clearance. Also, if someone is
> checking, for example, whether maxheight is specified for a particular
> bridge/way, they don't have to go searching for some random node
> "near" the bridge.

Problem with sharing the node between the bridge and way underneath is that you 
then end up with an intersection.  This would then confuse routers and 
renderers.

I would suggest splitting the way under the bridge and tagging that section of 
way with the max_height tag.  This is consistent as it is a restriction for 
that section of way (assuming there are no intersections along the way.


> By the way, you can't place a node "under the bridge", unless it is
> indeed shared by the bridge, as all ways have zero width (right?).

Actually you can.  Place the node on the way under the bridge, then drag it so 
that it is where the bridge crosses the way but do not join it to the bridge.

-- 
Ross Scanlon 

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 3:31 PM, Liz wrote:
> On Tue, 28 Jul 2009, Roy Wallace wrote:
>> By the way, you can't place a node "under the bridge", unless it is
>> indeed shared by the bridge, as all ways have zero width (right?).
>
> Logically you can as they are on different layers.

Yes, that is "under" as in "closer to the centre of the earth", but
not "under" as in "if you look up you see the bottom of the bridge".

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Re: [talk-au] multiple use of nodes

[Elizabeth Dodd]

On Tue, 28 Jul 2009, John Smith wrote:
> > I updated the seek code to place + sport and well yea...
>
> Actually they all seem to be valid, named dive spots, so that example was
> wrong :)
should they be name= and sport=
rather than place= and sport=

-- 
BOFH excuse #421:

Domain controller not responding


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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 3:30 PM, John Smith wrote:
> --- On Tue, 28/7/09, Roy Wallace  wrote:
>
>> I would at least suggest that - if maxheight is applied to a node, as
>> you suggest - the node should be *shared* by the bridge (way) and the
>> way passing under. This makes it clearer that maxheight is
> The problem with this is that 2 ways sharing a node are physically connected 
> and this wouldn't be the case as one passes over the other.

Ah, of course. Problem.

> Searching for a node near the bridge would be easier than searching for a way 
> since the node would be in close proximity to the bridge and you search by 
> lat/lon rather than random nodes.

Um...the way would also be "close proximity to the bridge", because it
passes under it... I don't see how finding a "node near a bridge" is a
particularly elegant solution. And by random I mean the particular
node you choose would be arbitrary and in an arbitrary position. And
by arbitrary I mean without specific meaning.

>> By the way, you can't place a node "under the bridge", unless it is
>> indeed shared by the bridge, as all ways have zero width (right?).
>
> You can use the maxwidth tag to indicate the maximum width and object must be 
> to pass a restriction on the way, like an underpass of a bridge :)

I was referring to the width of the bridge. And sure, maxwidth exists
but I would say that OSM ways are stored as lines. Mathematically, I'm
saying a point cannot be "under" a line, unless it is on it.

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 3:37 PM, Ross Scanlon wrote:
> Roy Wallace  wrote:
> I would suggest splitting the way under the bridge and tagging that section 
> of way with the max_height tag.  This is consistent as it is a restriction 
> for that section of way (assuming there are no intersections along the way.

I'm starting to like this idea. But the problem with this is how to
define "that section of way", so as not to introduce a maintenance
nightmare. My suggestion would be that the section of way should
correspond to the section that is indeed physically *under* the bridge
(on the order of 10m-20m long, usually).

>> By the way, you can't place a node "under the bridge", unless it is
>> indeed shared by the bridge, as all ways have zero width (right?).
>
> Actually you can.  Place the node on the way under the bridge, then drag it 
> so that it is where the bridge crosses the way but do not join it to the 
> bridge.

Hmm, I suspect this may be tricky to edit, if you have two nodes
nearly on top of each other, near where the ways cross. Sounds messy
to me.

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Re: [talk-au] multiple use of nodes

[Ross Scanlon]

On Tue, 28 Jul 2009 15:40:40 +1000
Elizabeth Dodd  wrote:

> On Tue, 28 Jul 2009, John Smith wrote:
> > > I updated the seek code to place + sport and well yea...
> >
> > Actually they all seem to be valid, named dive spots, so that example was
> > wrong :)
> should they be name= and sport=
> rather than place= and sport=

Yes.

-- 
Cheers
Ross

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Re: [talk-au] [OSM-talk] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 3:45 PM, Maarten Deen wrote:
> Having a node shared between a bridge and the way
> underneath may solve one problem but introduces another (having to make a
> relation to indicate this physical route is not present).

Agreed.

> maxheight needs to be applied to the road it applies to. Not the structure
> that is going over it. If you want to do that (which is not that uncommon,
> water maps do it all the time), introduce another key.

Ok. So it seems the question now is, how should maxheight be "applied"
to roads passing under bridges? The only reasonable and maintainable
approach, in my opinion, is to apply it to the section of road that is
physically under the bridge. Any objections?

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Re: [talk-au] maxheight/height

[John Smith]

--- On Tue, 28/7/09, Roy Wallace  wrote:

> Um...the way would also be "close proximity to the bridge",
> because it
> passes under it... I don't see how finding a "node near a
> bridge" is a
> particularly elegant solution. And by random I mean the
> particular
> node you choose would be arbitrary and in an arbitrary
> position. And
> by arbitrary I mean without specific meaning.

The solution depends on what problem you are trying to solve, if you are trying 
to find attributes of a bridge or restrictions of a way, my suggestion solves 
the restrictions of a way I'm not trying to solve attributes of a bridge.

> I was referring to the width of the bridge. And sure,

A physical attribute like the bridge's full width, which differs to a 
restriction of maxwidth is just width=*

> maxwidth exists
> but I would say that OSM ways are stored as lines.
> Mathematically, I'm
> saying a point cannot be "under" a line, unless it is on
> it.

OSM doesn't store lines, it stores nodes, it stores ways and which nodes are 
memebers of that way and it stores relations and which ways are members of that 
relation.

You can easily locate any node within a certain radius of any given path (or 
line) between 2 nodes and do a database lookup which will spit out any results. 
This is something keep right already checks for so it's not difficult, just 
processor intensive on a large scale.

If you want to be really picky about this you have to remember that even 
straight "lines" aren't straight as we're talking about a curved surface of a 
sphere so if it's straight on a 2 dimensional plane then it would be curved on 
a spherical one and vice versa. :)


  

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Re: [talk-au] maxheight/height

[John Smith]

--- On Tue, 28/7/09, Roy Wallace  wrote:

> Yes, that is "under" as in "closer to the centre of the
> earth", but
> not "under" as in "if you look up you see the bottom of the
> bridge".

You are thinking of lines, but this isn't how data is stored or processed with 
OSM, everything is based on the premise of a node, and then you can connect 
that node to another node by using a way construct, but ways aren't lines they 
are a description of which nodes are connected to which nodes.


  

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Re: [talk-au] multiple use of nodes

[John Smith]

--- On Tue, 28/7/09, Elizabeth Dodd  wrote:

> should they be name= and sport=
> rather than place= and sport=

they were tagged as place=locality which seems to be a valid use of the tag, 
they still use a name tag as well.


  

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Re: [talk-au] maxheight/height

[John Smith]

--- On Tue, 28/7/09, Roy Wallace  wrote:

> I'm starting to like this idea. But the problem with this
> is how to
> define "that section of way", so as not to introduce a
> maintenance

You really don't want to pull on that thread, the same can be said for bridges 
or virtually any other reason a way is split, someone even made a comment about 
maxspeed splitting ways the other week.

It's a much bigger discussion than maxheight and one that probably should be 
addressed and you would need to attack it as an overall problem, not just for 
one issue.


  

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 3:58 PM, John Smith wrote:
>
> --- On Tue, 28/7/09, Roy Wallace  wrote:
> The solution depends on what problem you are trying to solve, if you are 
> trying to find attributes of a bridge or restrictions of a way, my suggestion 
> solves the restrictions of a way I'm not trying to solve attributes of a 
> bridge.

Well, if possible we should try and find a solution that solves both
problems. However, thus far this doesn't seem possible, and the
consensus does seem to be that restrictions of a way is of higher
priority.

But even for that, putting a node in an arbitrary location on a way
still seems inelegant to me.

> OSM doesn't store lines, it stores nodes, it stores ways and which nodes are 
> memebers of that way and it stores relations and which ways are members of 
> that relation.

A segment of a way is clearly a line between two points (nodes),
without inherent width (sure, it may be specified with width=*, but
it's not an inherent property of a way). Anyway, this is off topic.

What do you think of my suggestion? That the restriction should be
applied to the section of the way "that is indeed physically *under*
the bridge"?

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Re: [talk-au] [OSM-talk] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 4:17 PM, Maarten Deen wrote:
> IMHO it is not that important if the way with the limit is only just beneath
> the bridge, or is somewhat longer or is applied to nodes on either side of a
> bridge.
>
> I recently came across this example where the way with the maxheight is a lot
> longer than strictly necessary. For every day uses this does not really pose a
> problem.
> 

So the solution is "do whatever you want?" Hrmm...

A couple of potential problems with this: What if someone later adds a
way that intersects the way with the restriction? The restriction must
then be removed from the part of the way that is beyond the bridge -
but this user should not be expected to know that the restriction even
exists...

Also, for longer sections, it becomes less clear that the maxheight
restriction is in regard to the bridge (versus the law, power lines,
trees, buildings, or something else). For ways with multiple bridges
in close proximity, it may become unclear which bridge the restriction
applies to. etc etc...

It gets a bit sloppy...

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Re: [talk-au] maxheight/height

[Roy Wallace]

On Tue, Jul 28, 2009 at 4:05 PM, John Smith wrote:
> --- On Tue, 28/7/09, Roy Wallace  wrote:
>
>> I'm starting to like this idea. But the problem with this
>> is how to
>> define "that section of way", so as not to introduce a
>> maintenance
>
> You really don't want to pull on that thread, the same can be said for 
> bridges or virtually any other reason a way is split, someone even made a 
> comment about maxspeed splitting ways the other week.
>
> It's a much bigger discussion than maxheight and one that probably should be 
> addressed and you would need to attack it as an overall problem, not just for 
> one issue.

For maxspeed (your example), the restriction should be applied to the
section of way on which the restriction applies. For maxheight (I
would argue), the restriction should be applied to the section of way
on which the restriction applies - and for bridges, it applies under
the bridge, and under the bridge only.

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Re: [talk-au] [OSM-talk] maxheight/height

[Ian Sergeant]

Maarten Deen wrote:

> I recently came across this example where the way with the
> maxheight is a lot
> longer than strictly necessary. For every day uses this does not
> really pose a problem.

Roy Wallace  wrote:

> A couple of potential problems with this: What if someone later adds a
> way that intersects the way with the restriction? The restriction must
> then be removed from the part of the way that is beyond the bridge -
> but this user should not be expected to know that the restriction even
> exists...

This is self evident - we map what is on the ground, and we apply the
restriction to the section of the way for which the restriction applies.

If a service road for a carpark has a restriction for the entire carpark,
even if it is just caused by the danger associated with one or two
low-hanging sprinklers, or a pipe,  the restriction applies to the entire
service road, and not just directly under the sprinklers.

If a motorway has a restriction for a motorway section, because of a low
bridge, the restriction applies to the section.  A higher vehicle is not
permitted on that motorway section.

If a country lane has a low bridge, the restriction usually only applies to
the road section under the bridge, a higher vehicle is usually unrestricted
except when it passes the bridge.

Applying a restriction to a way where there isn't a restriction, is clearly
an error, and should be corrected by the next OSMer to pass that way.

Ian.


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