Highway=construction rendering problems

[jeisenbe]

This issue is a follow-up to #2595.

• It has been suggested that highways under construction (construction=) should have the same width like their finished counterparts (highway=) on a given zoom level. However, this will lead to much wider highway=construction with construction=motorway/trunk/primary-tertiary on high zoom levels. This will make the following issue more prominent

(Partially fixed by #3580 for narrower roads like highway=service)

• Dashed white and colored lines are quite prominent. This is problem is reduced at high zoom levels currently, because highway=construction is rendered much narrower than major highways (motorway thru tertiary). It is very obvious right now with highway=service vs construction=service at z14 to z16, and with highway=residential vs construction=residential. If we make the motorways thru primary wider at lower zoom levels, they will appear very prominent.

• This could be fixed for motorway thru primary by using light gray instead of white for the dashes, and adjusting the length of the dashes vs the fill color, as suggested in: Construction highways width optimizations #2595 (comment)

• However, this is harder to fix for secondary highways, where the lightness is high, and for minor highways which are rendered in white

• Highway=construction does not follow proper layering order. Link roads (eg construction=motorway_link) can render on top of construction=motorway, and minor highways sometimes render on to of major highways. The layering order will sometimes reverse between different zoom levels.

• This would need a new SQL query, or separating teach construction=* type into a separate feature, I think? - fixed by PRs Fix layering order for "construction=*" highway categories #3646 and Fix layering order for highway=construction by adding z-order for construction=* values #4055

• [ ] Highway=raceway does not have a specific rendering for construction=raceway

-- This is not be worth fixing, there are only 3 locations in the globe with this tag.

• [ ] The current highway=construction style is not very intuitive. It might be considered a different road surface; for example, some topographic maps use similar patterns to represent unpaved roads (eg USGS).

Examples:
(Cardiff, Wales) z16 - layering problems

z17

z18

Test area:
z14

z15

[jeisenbe]

Thank you for merging #3580, @matthijsmelissen
Most of the issues above are still relevant.

Does anyone know how to fix the third problem above:
"Highway=construction does not follow proper layering order. Link roads (eg construction=motorway_link) can render on top of construction=motorway, and minor highways sometimes render on to of major highways. The layering order will sometimes reverse between different zoom levels."

I believe there is a "z order" function for highways which is actually part of the database import process. Is that correct? Is there a way to make the different types of construction=* fit into the priority system so that they layer consistently?

@pnorman?

[pnorman]

"Highway=construction does not follow proper layering order. Link roads (eg construction=motorway_link) can render on top of construction=motorway, and minor highways sometimes render on to of major highways. The layering order will sometimes reverse between different zoom levels."

If it's inconsistent between zooms, we've got a bug different than it being the wrong order.

I believe there is a "z order" function for highways which is actually part of the database import process. Is that correct? Is there a way to make the different types of construction=* fit into the priority system so that they layer consistently?

Yes. Right now highway=construction gets imported with z=10

openstreetmap-carto/openstreetmap-carto.lua

Line 207 in 295d65d

construction = {z = 10, roads = false}

[jeisenbe]

Changing z_order function has to wait till next database reload.