Talk:Key:position

How is this tag used?

The current text does not make sense to me. The description says "Relative distance between the feature and another one at which the first points to." What does this mean? Is the value a number of meters from the tagged feature to another object? How is a mapper supposed to know what the other object is? --Jeisenbe (talk) 03:49, 1 March 2020 (UTC)

For example, here is a marker node with position:

"type": "node",
 "id": 1691975382,
 "lat": 49.3994991,
 "lon": 8.1001699,
 "tags": {
   "colour": "yellow",
   "marker": "post",
   "operator": "creos",
   "position": "1.0;0;3.6;90",
   "ref": "B162",
   "utility": "gas"

What does "position=1.0;0;3.6;90" mean? This is very confusing. Where did these values come from? An import? --Jeisenbe (talk) 05:33, 1 March 2020 (UTC)

It means you'll find designated feature located at 1 meter left and 3.6 meters front of the marker you are facing. 90 sounds like an error to me Fanfouer (talk) 15:36, 1 March 2020 (UTC)

Some examples were added to Talk:Key:marker#Clarify_use_and_meaning_and_purpose_of_the_.22position.3D.22_key showing how they are listed on French gas markers, but it's still not clear what each part means. --Jeisenbe (talk) 11:23, 1 March 2020 (UTC)

I've updated the page to give a defintion for left, right, front... Fanfouer (talk) 15:36, 1 March 2020 (UTC)

Why is this tag needed?

Why would it be necessary to tag the distance from a sign to a fire hydrant, when the other object can also be mapped in the database? Database users can determine the distance between two nodes, or a node and a way, with simple calculations. Why should this be mapped? --Jeisenbe (talk) 03:49, 1 March 2020 (UTC)

Those values are read on ground (directly written on markers, see examples). Like any information got from ground, it's important to have a placeholder to put it. Distance between geometries doesn't necessarily reflect the reality thus it's interesting to compare with what is available directly in place and eventually correct appropriately. Fanfouer (talk) 15:36, 1 March 2020 (UTC)

Standard practice is Openstreetmap has been to read the information on a sign (like a max speed sign) and then add this to the appropriate object (like a highway way). It's not necessary to also map the position of the sign or the text which is written on the sign. In this case I suppose it's not harmful, but mappers are wasting their time adding these details, which should be correctly entered by the geometry of the map feature (the hydrant, or cable, or pipeline). Openstreetmap is a database for making maps and routing applications, we are not trying to copy aerial imagery + streetview photos directly, but rather to abstractly represent them in a useful, consistent, simple and verifiable way. Another issue is that this tag is designed specifically for the way that French utility markers are designed. I don't think they are listed this way in other countries, so it would be much harder to use the tag elsewhere. --Jeisenbe (talk) 02:09, 2 March 2020 (UTC)

As I see official services (even ministries) in France looking for road signs databases (which doesn't exist actually) and the value they're about to put in it, I think OSM is perfect to map even trafic signs and the text written on them. Mapping traffic signs along road tagging as well is useful to check consistency : a sign marking a change in speed limit makes the same change on the road consistent. Mapping poles or large sign panels is also useful for accident studies: a car hitting an unprotected pole will be in worse shape than if it won't hit no pole at all.

Back to markers, the same logic applies. Providing read values from ground greatly reinforce data quality as we can check against multiple sources where expected. Most of all : it exists on ground so why can't we map it? Fanfouer (talk) 22:43, 2 March 2020 (UTC)

Two meanings of <heading> vs position:heading

Now <heading> is described as "The direction the marker is facing in degrees (0 .. 360). It may be measured by a compass, but is usually also stored as EXIF value in pictures taken by modern smartphones (don't forget to subtract 180°)." but "position:heading" is described as "Angle between the front face of marker and a line towards the marked feature". That's quite different.

Which one is correct? Or is this used in both ways? --Jeisenbe (talk) 02:44, 2 March 2020 (UTC)

To me it's the same thing. It should be described as drawn in the illustration picture of the key. The direct angle between the face direction of marker and a line towards the feature Fanfouer (talk) 22:45, 2 March 2020 (UTC)

Meaning of <distance> and position:distance

Now the page has contradictory definitions of <distance> / position:distance - in one example it is "The hydrant is located 6.4 meters directly in front of the sign (so behind you if you look at the marker on the picture)." But the others claim that the feature should be that far behind the sign. Can we clarify if this is consistent? Are negative values like "-8.4." used if the feature is located in the opposite direction? Or is the <heading> used in this case? Maybe it's different for each type of utility? --Jeisenbe (talk) 22:24, 2 March 2020 (UTC)

I don't get any contradiction in what is written on the page. If you look at the marker, marked feature is necessarily behind you and you have to walk for the given distance in opposite direction to reach it. Fanfouer (talk) 22:47, 2 March 2020 (UTC)