roof:slope:direction in OSM Wiki

Dear all, I realize, that there are 5 486 elements tagged as: roof:slope:direction
This tag was not standarized by S3DB is aber widely used.
Should we take it up in the S3DB specification?
Some newbies asked me after exactly definition of rotation angle, this is the reasonb for my question.

There was some discussion about that tag here. As I remember the result was that roof:direction is preferred. It looks that current meaning it the opposite of what you add to SB3D wiki page, and it mean from roof top to roof bottom:

So, what should we do? We have two different standards and every week more objects tagged as roof:slope:direction

We should contact Cactusbone because F4 has set by his support the standard. The best supported method put through automatically. Most 3D-mapper tagg for the renderer :wink:

@marek: roof:direction (Dach:Richtung) ist leicht missverständlich (es könnte auch die Firstrichtung gemeint sein) und daher nicht mein Favorit. Lieber wäre mir roof:slope_dirction gewesen, aber da halte ich mich doch letztendlich an meine obige Feststellung :wink:


we should keep/use roof:direction and ask F4 to support it, too as most/more renderers support that tag.

Anyway, the wiki should be fixed. The description for the roof:slope:direction is not very descriptive imho (the description for roof:direction is). The image does not help neither and starts to bloat the page. It’s a Simple schema after all :slight_smile: If we’d make a decision for using roof:slope:direction instead of roof:direction or even allowing both, why not simply use the existing text in the comment column?

Still, my 5 cents, make it short, use roof:direction and use the semantics of that tag.

Well, dear f4 friends: now is the time for your 10 cents in this discussion…

f4map handles all 3 tags as the same : roof:direction, roof:slope:direction, building:roof:slope:direction

it should either be a string orientation (N, NORTH, NNE, and so on) or an angle in degree from north clockwise.

direction is used from top of the roof to the bottom (for skillion) - this should match “back to front” :slight_smile:

I’ll remove building:roof:slope:direction since it’s not used at all. I don’t know why we have this one.

I think front and back of a roof is kinda hard to grasp, whereas top and bottom are easy, but do not apply well to all roofs.
direction is mainly use for skillion, so top and bottom do match back and front. any other roof where direction is needed ?

When you do it, please use a bot and rename used elements and inform all users about that.

The direction is needed for most types of roofs, with very few exceptions (e.g. dome, onion). I’ve made this illustration of the meaning of roof:direction:

Note that with some roof shapes (such as hipped or gabled), there are two possible directions that yield the same result.

The “back to front” definition is based on the direction key. It can also be phrased as “the direction the roof is facing”.

simply put “downslope direction”

here’s current usage for direction (both tags) with roof


so most of the time direction is used to indicate top to bottom

maybe we should create the roof:direction page to explain what it means, including tordanik drawing and a few examples ?

we should not be using “back to front” in the definition if back and front are defined by the direction value.

“the direction the roof is facing” is better, “downslope direction” is great too :slight_smile:

Yes, please do it!

So if I’m reading the previous posts right, the plan is to add a page that documents roof:direction in more detail, and advertise using this tag instead of any alternatives? I would be happy with that. :slight_smile:

As for the “downslope direction”: That definition would unfortunately be ambiguous with roof shapes such as “hipped”, as there are multiple contradicting downslope directions. So we will have to use the more complex (but also precise) definitions.

Edit: After writing this, I noticed that Cactusbone had already started a documentation page. Thanks for taking initiative! I’ve expanded and (hopefully) improved the content a bit, I hope you don’t mind.

Yep it’s better now ! Thanks :slight_smile:

direction value is often used for skillion roofs. In this case the specified angle is interpreted independently from the building footprint. I does not not snap to any edge angle of the footprint, which makes it very versatile for modelling complex shapes. At least I found many examples, which would not work otherwise.
What about the other roof types? Should the direction snap to the “front” edge (orthogonal)? Results could be weird if the value doesnt match exactly.
There is already roof:orientation=along/across with a similar meaning. It is used 100000+ times.

f4map only uses direction for skillion.
we do not snap at all (but we should for cardinal directions because they’re not that precise)

for some roofs, along/across is not enough to know how to render it (saltbox and sawtooth for example)
but it whould make sense to snap for those cases. (maybe only for cardinals too, allowing for weird roof not aligned on the body of the building)

OSM2World is the opposite here, it snaps all values to a way segment of the building outline.

I know that this isn’t ideal either, as not all roofs are aligned to the building walls. So always snapping makes some cases impossible to model. Only snapping with cardinal directions could be an option, though.

It would be good to agree on a defined behaviour here.

same with osg-maps. no snapping at all. Only roof:slope:direction in combination with skillion
cardinal directions could trigger snapping.

Is there a plan to rename all similar tags to “roof:direction”? I don’t think that it could lead to inconsistency… :slight_smile: