[OSM-newbies] highway=traffic_signals

[Dave F.]

James Ewen wrote:
> On Sat, Apr 10, 2010 at 5:01 AM, Dave F. <davefox at madasafish.com> wrote:
>
>
>   
>>> What about the set of light underneath the railway overpass on the
>>> east side of the roadway? You never placed a node for them!
>>>       
>> There aren't any. The pedestrian crossing affects the other signals.
>>     
>
> http://tinyurl.com/y965w7r
>
> You should be able to see the lights in that Google Street View. They
> would be pretty hard to miss. If you're going to micro map the other
> three light poles, then this one should be included as well.
>   

Right, OK, let me clarify my understanding of traffic lights. The nodes 
I place represent not only the actual lights but also where the vehicles 
are meant to halt. I see it as a type of barrier.
That pole is a combination of two lights for traffic travelling 
different directions who's halts are positioned at the nodes.
Similar to the one in the middle of the pedestrian crossing.

>   
>> I'm not convinced by the use of the word abstraction to describe a map -
>> it's just a representation.
>>     
>
> Webster's Dictionary says:
>
> Abstraction:
> The act process of leaving out of consideration one or more properties
> of a complex object so as to attend to others;
>
> Representation:
> That which represents. Specifically: (a) A likeness, a picture, or a model;
>
> Kind of the same thing, huh?
>
>   
>> I'm trying to map as accurate a representation I can given the tools &
>> time I have available to me. Placing the three nodes is *more* (but not
>> fully) accurate.
>> I will continue to map in this way to make the map more useful.
>>     
>
> Useful to whom? As Pieren stated, statistically, more people represent
> traffic signals with a node at the intersection of the ways, not some
> distance away from the controlled intersection.
>   

That doesn't necessarily make it right.

> As for your suggestion that one can determine which direction the
> lights apply to by calculation based on locality rules, one does not
> have to do this when the node is placed at the intersection of the
> ways.
>
> The example below on Rotherham would suggest that the eastbound
> traffic only has to stop, when in fact both directions have to stop
> for that light.
>   
Because of it failings which I pointed out below
>   
>>> Based on looking at the first intersection that you have mapped, I
>>> would assume that the lights on Rotherham Road in the second example
>>> would be controlling the intersection with Cliff Hill, where in fact
>>> the light on Rotherham is a pedestrian controlled light for a
>>> crosswalk, and there are no lights at Cliff Hill.
>>>
>>>       
>> That's a failing on three counts:
>>
>> 1. The tagging is not accurate (no crossing tag)
>>     
>
> I guess then that your representation is a failing as well, as you
> have no crossing tag.
>   

Not sure what you mean. The one nearest the railway does.

>   
>> 2.The rendering doesn't distinguish between a traffic-light & a separate
>> pedestrian crossing.
>> 3. (to a lesser extent) You not understanding the representation. Don't
>> you think that as there should be three nodes, that one might represent
>> something different?
>>     
>
> Exactly my point. A traffic signal node in the middle of a single way
> would be interpreted as controlling that point (node). A traffic
> signal node at an intersection would be interpreted as a traffic
> signal controlling that intersection (node). Both the same
> interpretation.
>   

For my example, where would you put the pedestrian crossing?
If you add it as a separate node that would a misrepresentation as 
there's not a separate set of lights.

> In the Rotherham Road instance, I'm going to assume that I will find a
> traffic signal mid-block, and not at the intersection of Rotherham
> Road and Cliff Hill. Further down the road at Rotherham Road and
> Addison Road, I'm going to assume that I will find a set of traffic
> lights controlling the intersection.
>
> With your method, if I find a traffic signal in the middle of a way, I
> have to scan the adjacent area to try and determine if I am looking at
> a traffic signal controlling traffic on that way, or if it is a
> traffic signal that is part of a larger set controlling an
> intersection at some distance away from the node.
>   

OK, let's assume the renderings been improved & they are different for 
traffic lights & pedestrian crossings.
Other than a crossing I can't think of a reason why there would be 
lights on a road with no junctions so a traffic light would by default 
be used at an intersection.
> BTW, isn't a discussion about how to tag various items a good thing
> for a newbies list? The concepts here about micromapping of traffic
> signals can be extrapolated into other areas as well. 

I agree. Some think long discussions on here bores & confuses the 
newbies, & they should be moved to other groups, but as long as they're 
(hopefully) clear & don't descend into a slanging match, I see no problem.

> I am still
> reluctant to map a whole lot of details because I do not have a well
> developed set of "rules" that I would use. I am still gathering
> information about how to map things, and I've been a part of the OSM
> community for a few years now. I don't want to spend a whole lot of
> time and effort doing things wrong only to have to go back and redo
> all of the work to make it correct.

I see it as learning on the job. I mapped things then months later gone 
back & added/corrected them as I learnt.
I think the map is better with something that may not be fully complete 
or correct rather than empty.

Cheers
Dave F.