[OSM-dev] Suggestion about design of OSM data structure (take out segment component)

[Frederik Ramm]

Hi,

> Your argument is not valid because you are assuming that branching ways 
> (Y-shaped) are 2 ways direction but they may be one way direction in the 
> real life!

That doesn't make my argument any less valid for those ways that are not 
oneways. Your picture (2) is what I had in mind; you are right in saying 
that if the main road is another type of road it needs to be split 
anyway, but we often have a residential road with residential branches, 
so they're all the same type.

It is desirable to split these into individual ways, even today, because 
it makes things easier for renderers and so on. And it is possible. All 
I'm saying is that it will require a lot of manual work. Even if you 
could prove that, in theory, such ways couldn't exist because they 
violate some rule, I can tell you from practice that they do.

About areas with holes:
> Without segments, I still can use simple way to model area with hole.
> For example: I have 11 nodes. Node: 1, 2, 3, 4, 10, 11 form the outer 
> ring clockwise and nodes: 5, 6, 7, 8, 9 form inner ring anticlockwise. 
> Two rings joined at node 4 and 5.

That's a bad way to do it. Imagine you have an area drawn with contours 
(for example, lakes sometimes have a darker blue contour and a light 
blue fill) - the contour would run straight through your lake from 4 to 5!

> 1. When you design data structure for map, you need to save any space as 
> much as possible because map data are very huge.

Amount of data hasn't been a problem until now. If it were a problem, 
then we would probably stop using free-form keys and values for our tags 
and replace them with integers, and we would stop tagging every single 
node, segment, and way with a "created_by" tag ;-)

> 2. Data structure must be simple enough so that other program can 
> process your data.

I agree that ditching segments would make things easier. Almost 
everybody agrees that that's the case. We're currently more or less 
waiting for someone to program the changes necessary on all levels - 
API/database, renderers, editors, etc.

> I hope osm foundation will consider my arguments and take out the 
> segment component from planet.osm xml file.

Whether or not the OSM Foundation - which, technically, isn't the boss 
in this project but let us assume for a moment they were - approves the 
idea of removing segments will depend very much on whether the 
appropriate code exists at that time. This project is not normally run 
top-down (decision makers decide, then programmers write code) but the 
other way round. Or, to say it more bluntly: It's not going to happen 
unless someone writes the code.

But I'd welcome someone to do it.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'