Proposal:Aeroway=holding position line
| aeroway=holding position line | |
|---|---|
| Proposal status: | Draft (under way) |
| Proposed by: | Mboeringa |
| Tagging: | aeroway=holding_position_line |
| Applies to: | |
| Definition: | A line behind which aircraft are considered clear of a crossing way |
| Statistics: | |
| Draft started: | 2022-08-31 |
Proposal
A tag to represent the actual real world painted holding position line on the tarmac of a taxi-, or less common, runway.
Rationale
The current tag for holding positions, aeroway=holding_position (https://wiki.openstreetmap.org/wiki/Tag:aeroway%3Dholding_position), is allowed to be both nodes and ways. However, in reality, there are different uses for holding positions: e.g. either as stop node for routing purposes in a flight simulator, or to cartographically display the holding position's line on an airport's map. These two purposes are in conflict with each other, and in practice may lead to edit wars, where nodes are replaced by ways for drawing maps, and subsequently edited back to nodes for routing purposes.
To solve this issue, it is best to have a separate tag for tagging the actual line on the tarmac.
While this does add a minor form of duplication, it has to be realized that not only the purposes of the nodes and ways of holding positions are distinct, but the object themselves warrant distinguishing them:
- The line on the tarmac may be placed asymmetrically in reality compared to the yellow center line on a taxiway, which means that automatically drawing a perpendicular line on the position of an aeroway=holding_position node object, will not properly represent "what is on the ground". An automatically drawn line may be to short on one or more ends compared to the "on the ground truth"
- An aeroway=holding_position_line object may in reality have a bend on the tarmac. Such situations occur where taxiways split at a junction. This again pleads for a separate way object that can represent the true extent and form of the line on the tarmac, rather than trying to derive it from the node only.
- Most holding positions have a distinct orientation relative to their associated runway. This can be represented by carefully setting the correct digitization direction of a way object, see sections below, but is more difficult to represent as just a node.
Tagging
aeroway=holding_position_line
How To Map
- Draw a way through the center of the painting work on the tarmac representing the holding position. Draw the entire length as visible in the aerial imagery, from one side of the taxiway to another. Add an aeroway=holding_position node object where the way crossed the taxiway line object, or, if already present, draw the line through the node.
- Add the aeroway=holding_position_line tag to the way object drawn.
- Tag the type of the holding position as either holding_position:type=runway/LAHSO/ILS/intermediate. For explanation of these tags, see the https://wiki.openstreetmap.org/wiki/Tag:aeroway%3Dholding_position Wiki page.
- Tag the identification code of the holding position as the ref tag, e.g. "24-06".
- Make sure both the aeroway=holding_position node and aeroway=holding_position_line way object have holding_position:type=x and ref=x tagged!
Take care of the digitization direction of the line!
While ILS and intermediate holding positions have symmetrical painted linework on the tarmac, runway holding positions don't, they are oriented in a particular manner with the toothing towards the runway. This resembles e.g. the situation of a tag like natural=cliff. Even for ILS holding positions, even though having symmetrical painting work, the actual position of the identification code of the holding position on the tarmac, is oriented in a specific way compared to the runway, with the identification code being "below" the linework on the tarmac compared to the runway a plane is about to enter. It is therefor paramount, to always digitize the line in the correct direction, to allow renderers to draw the identification code on the correct side and in the correct orientation compared to the runway.
Additionally, from a cartographic point of view, any labels of the holding position's 'ref' tag, should preferably be similar to the "on-the-ground" orientation, which usually means the runways identification is painted "below" the runway holding line, on the opposite side of the holding line's toothing. In order to replicate this in a map rendering framework, GIS or CAD system based on OpenStreetMap data, it is best if the line is oriented with the left side towards the runway, as most systems will label a line left to right / begin point to end point according to left-to-right Latin script. This results in the label being "upside-down" compared to runway orientation if the digitization direction is "wrong".
I therefor suggest introducing a recommendation to always digitize the holding line in a standard manner, e.g.:
"The direction of the way should be so that the runway is on the left side of the way direction."
to remember this one, a phrase like "(L)eft side is where you (L)and" might help.
Examples
Rendering
Rendering example with correctly drawn symbols and identification labels for runway holding positions due to standardized digitization direction:
Features/Pages affected
The current page for aeroway=holding_position (https://wiki.openstreetmap.org/wiki/Tag:aeroway%3Dholding_position) will need to be edited to only allow for nodes as valid object type, and reference this page for drawing the ways of the actual object on the ground.
Comments
Please comment on the discussion page.