Trying to make multipolygon from type=boundary

[sn4k3ch4rm3r]

I'm trying to get Hungarian national parks to show correctly.
Example: https://www.openstreetmap.org/relation/6106836
If I don't do much processing it's missing some parts:

Using the relation_scan_function I was able to get every part of it, and the outline appears to be correct, but turning it into a polygon, it appears to be inside out:

This is the process.lua I was able to put together based on the docs and the OMT process.lua

function relation_scan_function(relation)
	if relation:Find("type")=="boundary" and relation:Find("boundary")=="national_park" then
		relation:Accept()
	end
end

function way_function(way)
	local isBoundary = false
	local name = ""
	while true do
		local rel = way:NextRelation()
		if not rel then break end
		isBoundary = true
		if name == "" then
			name = way:FindInRelation("name")
		end
	end

	if isBoundary then
		way:Layer("park", true)
		way:Attribute("class", "national_park")
		way:Attribute("name", name)
	end
end

[systemed]

I doubt that'll work like that. tilemaker has special handling for multipolygon relations (i.e. type=multipolygon). It looks like boundary relations probably need to be processed that way, rather than with relation_scan_function.

I imagine you could get some way towards this by patching read_pbf.cpp:

(in PbfReader::ScanRelations)

	int typeKey = findStringPosition(pb, "type");
	int mpKey   = findStringPosition(pb, "multipolygon");
	int boundaryKey = findStringPosition(pb, "boundary");

	for (int j=0; j<pg.relations_size(); j++) {
		Relation pbfRelation = pg.relations(j);
		bool isMultiPolygon = (find(pbfRelation.keys().begin(), pbfRelation.keys().end(), typeKey) != pbfRelation.keys().end()) &&
		                      ((find(pbfRelation.vals().begin(), pbfRelation.vals().end(), mpKey ) != pbfRelation.vals().end()) ||
		                       (find(pbfRelation.vals().begin(), pbfRelation.vals().end(), boundaryKey) != pbfRelation.vals().end()));

(in PbfReader::ReadRelations)

		int typeKey = findStringPosition(pb, "type");
		int mpKey   = findStringPosition(pb, "multipolygon");
		int boundaryKey = findStringPosition(pb, "boundary");
		int innerKey= findStringPosition(pb, "inner");
		//int outerKey= findStringPosition(pb, "outer");
		if (typeKey >-1 && mpKey>-1) {
			for (int j=0; j<pg.relations_size(); j++) {
				Relation pbfRelation = pg.relations(j);
				bool isMultiPolygon = (find(pbfRelation.keys().begin(), pbfRelation.keys().end(), typeKey) != pbfRelation.keys().end()) &&
		                      ((find(pbfRelation.vals().begin(), pbfRelation.vals().end(), mpKey ) != pbfRelation.vals().end()) ||
		                       (find(pbfRelation.vals().begin(), pbfRelation.vals().end(), boundaryKey) != pbfRelation.vals().end()));

(I haven't tried this!)

[sn4k3ch4rm3r]

Thank you, it seems to have worked.

[systemed]

Excellent. I'll look at making this a permanent fix.

[BenOnTrack]

Hi, do you mind sharing your solution @sn4k3ch4rm3r ?
I have the exact same issue with https://www.openstreetmap.org/relation/3659121#map=12/-36.9576/174.5459

If we should handle the "boundary" as multipolygon with the solution provided above, then how can I pick the ways to re-build this relation R3659121 and store them in a specific layer knowing those ways (in my example) have no tags?

thanks in advance for your feedback

[systemed]

You should find that #508 fixes this. You will need your way_function to look for boundary=protected_area and to act accordingly.

[systemed]

I've reworked #508 a bit and you can now handle a multipolygon boundary by:

• accepting the boundary in relation_scan_function
• writing it to a layer in relation_function (not way_function)

tilemaker will pick up on type=boundary and the inner/outer roles, and automatically handle it as a multipolygon geometry.

There's an example of how to do this in the comment for #508.

[BenOnTrack]

It works great, I'm so excited !
Thanks so much @systemed
Ben.