[OSM-newbies] highway=traffic_signals

[James Ewen]

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.

> 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.

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.

>> 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.

> 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.

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.

As I said previously, this is the biggest detriment of having a large
disparate group of individuals working on a project of this type. The
lack of implementation uniformity in representation makes it difficult
for the end user to interpret the resultant map.

Go ahead and continue to map your area as you see fit. We can not tell
you that you are doing anything wrong as there is no firm rule in
place that states "It must be done this way!"

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 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.

James
VE6SRV